I don't think this comparison is terribly helpful. The question I think we're all wanting answered is: if you're OCTANE LIMITED, say building a pump gas motor, which is a better approach, low-compression/high-boost, or higher-compression/low-boost.
get a 9:5.1 compression, high compression will develop knock eventually if a mistake is made, then you need a rebuild, plus you'll always need high octane gas, no exceptions.. High compression is like having a gf who is only happy when you kiss her ass, the day you don't, she dumps you n you're stuck with pink eye..lol
The issue we had back in the day with high static CR's was timing, the quality of the head gaskets and the carb technology. Today, you can pull timing out of the motor exactly where you want it, tunable closed loop MPI with knock sensors and MLS head gaskets, so yes, I feel you can run higher static ratio's and pick up torque down in the lower RPM band, especially with turbo's.
@@albertgaspar627 Yeah, I'm doing a Saturn 1.9 LDOHC build on mine with 10 to1 comp with low boost 8-10 PSI and an E85 blend. Building the most velocity instead of volume, JE forged pistons, ARP main and head studs, knife edged 3rd gen crank and lower tie plate, port and polished head, mild intake deshrouding, mild bowl blending, dual intake cams, ported polished intake manifold, bigger TBI and low boost E85 like I mentioned.I figure it'll be better if the machine shop builds it well. The car is light with the polymer panels, carbon fiber hood from Seibon, and the 15X7 Einkei RPF1's that are 9.8LBS each, and Mfactory limited slip differential. Should be a fun ride to surprise some people as well with my little baby car, ha ha...lol My engine is light too at 220 LBS, half the weight almost of a normal 4 banger from the lost foam casting..lol
@@junechris sounds like a nice design, check out David Vizard's channel too. he does dyno work with headers, you might find some tech there to help the velocity you want by clearing out the combustion chamber as fast as you want to fill it in. As you know, the joy of DOHC is you can play around with overlap and lobe separation by moving the individual cams around instead of having to buy a new re-grind. I have a naturally aspired GM EcoTec 2.2 litre in the "pile" of project cars, would love to play with its potential since GM already went ahead and had a supercharged version (like the Saturn Ion). As you know, in a light car it can be a sweet piece when done right.
@@albertgaspar627 Yeah, I've heard about the cam options you mentioned about. Right before u messaged me, I was happy to find Ross makes forged pistons right in their catalog for the Saturns. And one of the other guys I spoke to on here was a 30+ year machinist that seems quite fond of the Ross ones in regard to the ring gap recommendations being more or less right on the money so i'm gonna relay that to my friend doing the build for me tomorrow.
Richard I think you're videos are fantastic my only issue is you rarely use pump fuel i understand the limitations and possible engine damage when testing but I think its what a large percentage of viewers run. I would love to see more of it. The power you get on hi octane would be unobtainable for a lot of us.
The only reason to run lower compression in my mind is if you don't have access to quality high octane fuels. Otherwise, more compression, the better, assuming you can time it/tune it correctly
Before even watching it I know the high compression one will make more power with boost because boost just enhances the NA curve of that engine. The better NA the better with boost.
You said it, the roots application is probably best off with the 8.5:1 long block. By my rough calculation, the 11 psi boost would have given you well over 1100 hp if not for the power needed to spin the blower, about 195 hp if the formula held true. That’s basically lots of heat added to the intake charge. If I had a couple GT-45s making that same 11 psi, I’d want the 10:1 or even more, EFI, and E85, too! That 540 would be a beast either way, I think.
If one wants to run high rpm and 30-40 psi boost, then 9:1 would be as low as I would ever go... Tuning becomes critical with higher compression, but will always make more power, and efficiency on daily drivers... The way the compression is made is also important, like having a dome piston with it down in the hole 60 thou would be asking for detonation and/or pre-ignition. Proper design combustion chamber is imperative for the proper platform.
For running on pump gas, I think it makes a difference how much boost you can run without running into detonation. The dynamic compression ratio based on cam specs is a big factor, too. Even though the static compression may be 10:1, the dynamic compression may be a lot lower with a big cam, so lots of variables there, tough to do a true apples to apples. Good stuff to talk about, though!
Higher compression with boost increases the likelihood of detonation. Lower compression gives more wiggle room to withstand that issue. If the tuning is spot on and the fuel has really high octane (91+), then the higher compression will not cause an issue. Lower compression is often recommended for boosted engines because it just allows for more error.
Even on pump gas I think the higher compression would be better. Off boost performance would be better and if you are tuning for maximum power for a given fuel the maximum output should be the same because the cylinder pressure where knock occurs would be the same.
I think this is an excellent question. Most people are going to be limited by the fuel octane availability, and I also dont see anyone else providing any data on this subject.
To answer the CR question just look at diesel tractor pulling. They use lower CR pistons so that more boost can be put into the engine. So yes, depending on the extra air to be added, lower static compression can be a benefit.
Absolutely, I run 8.5 CR in a LS stroker and it allows me to run way more boost than if I was at 11.5 CR. Plus the fact I don't have to worry about detonation.
the test that needed to be done would be to boost the both motors to the same cylinder pressure at TDC, the lower compression motor motor is in theory larger then. All compression done in the motor creates heat in the charge, compression done outside the motor with boost and intercoolers, results in more mass flow rate.
Modern engineers have things figured out by now and technology only gets better. It's easy to see what compression ratios are "safe" for a boosted engine by looking at modern flagship cars like the dodge demon, GT500, and ZL1. All posses compression ratios from 9.1-10. can forged and aftermarket engine components survive more abuse. Possibly, but many guys are fooled into thinking their engine has some magical abilities because it continues to live on a certain static compression ratio and boost level when in reality many times the engine has a cam with great overlap (lowering dynamic compression) or the engine has quality components and is just suffering through it. Another mistake is people think that any boost level on a said compression can be attained by lowering timing. In reality, an engine that creates knock from a product of heat due to the combined boost and compression ratio gives no attention to when the spark plug is told to ignite. This is why it's called pre-ignition.
I think the question is what the goal is. Absolute max power? Low CR and lots of boost wins. More return on boost than CR. Driveability with a flatter curve without spikey boost curves? Higher CR and slightly less PSI from the whistle bits.
From my experiences with low compression motors, they do an excellent job in colder places. Ohio, Minnesota etc. Low compression motors are amazing for torque gains. Gives you a different feeling when you put your foot on the pedal.
You CAN run a high boost on a high compression engine, IF!!! you have an inter-cooler. The problem with a super charger on a high compression engine, is temperature rise during compression. Too much compression could mean reaching temperatures high enough, for fuel to "auto-ignite", much like a diesel engine. The fuel may not wait for the spark. That pre ignition will destroy the engine. If you're going to boost, without inter-cooling, lower compression is a MUST! No matter what, I do recommend a high octane fuel on a boosted engine, because of its higher ignition temperature.
I would never consider 8.5:1 with that cam size and a limit of 11 psi. Flat torque curves are what win races and generate efficiency on the streets, not peak numbers. I once watched a video of BMW m7, 770hp 4.4 v8 outrun a late model Dodge Challenger at 1100 hp w/ blower from a 60 mph drag. 1100 hp is nothing to cough at, but the Bimmer just ate his lunch. Personally, I am about efficiency, and it is more about building what works than cool dyno digits. That's how I got an 11,000lb dually 5.9 Cummins to outrun an Audi A6, on a 62mm turbo, w/o melting down... And with 300k mi on the clock...
When you factor in limited octane, it comes down to the detonation limit of the compressed charge. 8.5 to 1 at 14lb of boost will have 250psi compressed where 10 to 1 will have that same compression pressure at 10lb of boost. the difference is the lower compression engine will have a larger combustion chamber with a larger charge at the same pressure. obviously at the same boost the more efficient higher compression ratio will make more power. But that only works with fuel that will tolerate it. Run the same engine on pump gas boosted to the detonation limit and I think the lower compression combo will come out on top.
I have recently taken a low boost paxton motor that was 8:5:1 to 11:1 in a corvette. I left 100hp on table for years by not running higher compression. Motor runs better, idles better, all drivability better. BUT it is compensated on boost by methanol injection … however it was at 8:5:1 also. So was winning combo foe me
Lower compression would be good in a drag week application to run pump gas on the street. I like E85 but no telling what availability would be on rou te. I would probably go 9:1-9.5:1. As you've proven Richie.....more efficient n/a the better the power will be boosted.
yeah i agree too, going too high in compression will eventually develop "knock" no matter what on a boosted application, n that's the reason many ppl end up selling their "builds"..lol i rather have a nice 9:5.1 compression as i have in my 2v n run pump gas or e85 n be good on boost..
The advantage of high compression with boost is the reduced effects of boost lag. The advantage of lower compression is you can run higher boost levels before grenading the engine. I think a low compression engine with the same components will live longer with high boost pressures.
Through my years I've found you will make more power on a higher compression engine. A lower compression engine really shines at very high boost 35psi + and large spark advance. You will detonate a higher compression engine allot easier. I would rather have low compression and high boost then higher compression and low boost.
I totally agree with you, they both have their place. You just have to build what it is you are building for. In a W.A. Street Machine, I'd run low CR for the "just in case" factor.
In a boat with crappy gas docs - no, in boat with severe load all the time - no, with out fresh water cooling - would help things , another aluminum head justification - IE 1 point of compression as a gift - I went with a roots from mooneyham for the sound and nostalgia and 8.8 - 1 with ICON pistons
If your concerned about drivability low compression higher boost on premium gas or e85. if drivability isn't a concerned and you're more all-out drag racing or weekend warrior you want higher compression racing fuel like e85 c16 C32 or methanol to control predetonation with high boost. You either have low compression 14 lb of boost premium fuel for E85 and get 1000 horsepower or high compression racing fuel or methanol had 7 pounds of boost and get 1000 horsepower. my opinion. P.s boost and hp numbers is just an example An actual true comparison is to have two Motors that are built the same with every part the same the only difference would be is ring Gap and compression ratio. but video has good information.
If you trailer your car to the track, yeah, go for the compression, because it's not gonna get hot enough. For a street car, choosing the lower compression offers your a better portfolio of benefits with boost. That said, 8.5 may not be necessary. 9.0-9.5 is fine with a big cam.
The 8 5 to 1 would last a lot longer due to the lower compression ratio,and you could run it a tad fat on E85 and drop the oil a 10K or 5K,be an easy one to love
I read an article that claimed higher compression in a boosted engine would tend to fight against itself… as the RPM increased, the pressure in the cylinders would also, thus keeping them from operating at their max n/a rev capability. Think of how hard it becomes to pump more air into a bicycle tire when it’s close to it’s rated psi. Maybe this inverse relationship explains why top fuel cars run such way low compression; they need the RPMs at the top end. 0:08
The book I recall reading - mid-late seventies era; I think the title was something like “super power” - spoke of 20% *underdrive* and 8 to 1 compression when running a Roots blower. (For routine-level street use, I think.)
As always great content... Haven’t seen you in a while, Hope all is well.. Really bummed you didn’t run the Higher compression motor with Boost? I think everyone was expecting that. Just Say’n As always great videos. Again, truly hope all is well with the family, etc...
Higher CR always makes more power but you're limited by the Detonation resistance of Fuel used. Boost increases the need for higher detonation resistance. High CR with boost is a very powerful combination, especially turbo as it spools much faster than a low CR motor
I'm running 11.3:1 compression E85 and 5 lbs of boost With the cam I'm using My effected compression is 15.47:1 I've done a few things to help Heat coated tops and dry lube on skirts Total seal gappless second ring gapped at .028 4.31 bore 4.25 stroke 496ci AFR heads with mirror polished combustion chambers. I don't have any problems
This might be more applicable to those of us with small cubes. One of the cool things about high compression is that it makes more power off boost. Makes for a car that's fun to drive on the street out of boost. Yeah, a low compression 454 is going to be fine around town, but think about a 2.0L.
I run 11.5 CR with 11 psi of roots blower boost. You can have both boost and compression. I do run water/meth injection to keep it safe when circuit lapping though. Which bypasses the need for E85 which is not very available in my part of the world. Can run in on straight 98 (RON) pump fuel though, no problems, just that it will start to pull timing as air intake gets hot.
Build a grand national 3.8! I made 730rwhp with a 76mm precision and hogged out iron heads. Then with a set of champion aluminum heads and a bump up to 4.1L, I made 1,032 rwhp with a/c and went 8.89@164 back in 2000. But we Buick people need some love
Back in the day it was 3 things, 1 fuel. Didn't have e85 at the pump, 2 didnt have computer software that could control things properly. 3 we didn't have you Richard.
It would be fine on 10:1 as long as the pistons gave top ring located lower than typical on NA. Considering other factors arectaken care of. The only way to truly test this is back to back on the same engine. Either swap pustons only, or swap heads as long as heads are exactly the same except combustion chamber size....
I’ve ran 9.25 :1 on 6 to 8 psi in a marine application , the problem is the load that exist in a boat to put that into perspective have you seen a brake pedal in a boat ? But we also have the biggest radiator there is that being lake water , so cool engine temps say 140 to 160 combined with aluminum heads , coated pistons , allows us to get away with a lil higher compression, but 10:1 in a marine app I mean I’d doit but wouldn’t recommend it to a customer
I’m going low compression on this one. Can’t see the 50 horse being worth the security the lower compression offers. Especially being able to make up the difference with more boost. And because I am a budget guy who is remarkably impatient… I’d also probably run it before I got the blower or turbos and just beat on that thing while running lawnmower gas and have a blast.
I was told to go with lower compression, and I was told a supercharger raises static compression. Moroever, for a lot of boost. I was told to consider alcohol, but I rather run pump gas 91 octane, so I was told not to run too much boost for a supercharger roots style application. I am curious what you think.
A missing element in your test: the cylinders exchange the same vol of air NA. Not so on boost. As a result, can you run more boost on the PA motor while achieving the SAME dynamic compression or peak cylinder pressures? It stands to reason you can. The net effect of using boost may be the larger compression volume of the PA motor would effectively act like a larger displacement and has the potential to make more power at the same peak cylinder pressures.
Higher static compression just requires less boost for the same power. This is why my LSA motor is 11:1 static. I don't have to spin the blower above its max efficiency to make the number I need...
4500 flanges offer better cylinder-to-cylinder distribution and a little straighter path down the intake runners over an equivalent 4150 intake, right? Let's be honest, fuel quality(and, later, emissions) is what has driven compression ratios since the earliest engines, and, today, fuel quality is as good as it's ever been. A better NA engine is a better power adder engine all said and done, it's better off of the power adder(minimal boost or not spraying it) and it's better on the power adder. This essentially goes back to "should you build your boosted engine, or just increase the boost?" - at the end of the day, 1000HP is still 1000HP, and an appropriate torque converter & gearing can band-aid any power curve(I mean, if they can make 1000lb-ft@1500RPM diesels work... Lol), so this may not be particularly relevant to the junkyard LS + Amazon turbo crowd - but, if you're building an engine, you're going to have to give me a hell of a reason why not to go high comp. There's applications where you want the greater safety margin from detonation for sure, but fuel quality is so good today, nevermind the availability of an alcohol fuel at the pump(E85), that the risk has fallen. It wasn't that long ago that everyone thought these Coyotes were going to be blowing up with boost because of their 11:1 stock compression - so much for that theory LOL. Maybe I'm biased though, we've been spec'ing out an engine build for my nephew's Mustang and, having grown up with the Modular scene, I was influenced by high comp + boost earlier. Needless to say, right from the beginning we've been planning on ~14:1 comp with softened chambers, and moderate boost in the future. Probably a 438" Windsor, probably high ports, and probably a Holley Hi-ram, controlled by a Terminator X... ...but nothing is set in stone until the money is spent of course, but we've already started with the TermX. Oh yea, and for an E85 'street car' of course lol
I think you hit the nail right on the head. I think back to how many bone stock LS2’s were running around with 10+ psi of boost on daily driven vehicles. Mostly Corvettes. 11:1 CR and stock ring gaps. That was before E85 was super popular too.
For the street on pump gas low compression for the win. Easier to control detonation. Why though would you recommend low compression for boat motors at wide open throttle say on E85? Is it the extra heat from the higher compression motor that causes problems????
As I understand it, it really comes down to engine management; that an ECU can figure out cylinder conditions by running a very, very low power signal through the plugs when not triggering combustion, absolutely blows my mind. At that point, it comes down to the better thermal efficiency of the higher compression, provided you can still run your desired boost/airflow without pre-detonation
@@richardholdener1727 yes - I can't find it now on a Google search so I wonder if I have a misunderstanding - a couple years ago, I read in my dad's Automotive Engineering that the high-end (read: German/Euro & Japanese) brands are using spark plugs to get a better idea of combustion chamber chemistry (because the impedance changes relative to air density and chemical composition). He recalls the tech as well, so chances are that I'm not crazy or making this up Point being....his Audi has an 11.5:1 CR turbo 4-banger. Engine management is changing what a "safe" CR for a boosted application is
I was hoping to see the same blower put on the higher cr motor but driven slower to make the same power as the highly boosted low cr motor and than figure out witch way was better.
This is only theoretical, but I think more compression and less boost would heat the incoming air less, while creating equal cylinder pressure. Thus MAYBE the air would denser. Sure, there's intercoolers, but that's more expense.
I can't see a high compression boosted engine being able to withstand the same octane fuel as a low compression engine with both running the same level of boost. The lower compression version could run more boost than the high compression and overcome the lower compression shortfall.
It all comes down to fuel choice and timing. The theory hasn't changed. You cant run high comp with high boost for pump fuel. e85 is a different story as already mentioned in the comments.
If the engine is not in a race only (or boat) application where a certain amount of practicality goes out the window, higher compression is the way to go, you'll make more power for a given amount of fuel, so the fuel system can be smaller and you don't have to stop at the pump as often. You will also make more power off boost which will make the thing easier/nicer to drive in a few different ways; it can compensate (a bit) for a wilder cam at low engine speeds making any low speed driving much nicer, it also means you might be able to shave a few 100 rpm off your stall on your torque converter. Modern ECUs can do closed loop boost control, knock retard, IAT retard, exhaust backpressure retard and table blending based on ethanol content; people are talking about driving on pump gas and lower comp being better, but really all you would need to do is either change map with slightly lower boost and less timing, or do nothing and let the ecu pull timing if your ECU is tuned correctly.
Not exactly. Knock sensors are not exactly scientific level sensors and some setups can suffer catastrophic damage almost instantly if they encounter detonation. It takes a dyno and good tuner to find that line in the sand. You add tiny amounts of timing until the motor no longer produces increased output. Then you back it off, to each tuners opinion, on what they feel is adequate safety margin...
For a race engine there's no need for low compression I see dudes running 13to1 with turbos but if it's a street car then lower compression would allow you to drive it on normal gas you just wouldn't be able to really beat on it with the normal gas.
The higher the compression the lower the Boost. I want to try 12.5:1 at 4-8lb of boost in a LS3 or K24/20 head. Twin Garrett 3776's or single Garrett 3776 for the K, electronic wastegate. Start at 1lb. and work up to the max. I'd stop at 8lb. even if it took it like a champ. 4 boost settings, 2lb. 4lb. 6lb and 8lb.
All depends on the fuel... In a boat buying premium pump gas at the fuel dock, I'd want the 8.5 motor. If I could reliably get decent E-85, the 10 motor would be OK. But we only have one E-85 pump in the whole county ... And no-one can afford race gas on the street, out cruisin ...
Richard, I think you need to read a goid article in DC Sport magazine that explains very well what CR is the best for your application. Basically higher CR shines up to 2 Bar of boost. After that point lower CR takes over. You need to taje a look at their table which represents both - volumetric efficiency and thermal efficiency. For instance in my forced induction application with 3 Bar of boost I use 8.5 CR. Had I used 2 Bar of boost or less I would've raised CR up to 10.
Thnx-I understand thermal and volumetric efficiency and the trade offs-they exist in NA motors as well-which is why continued increases in static compression don't continue to yield a strict % change in power
Yes, as you well know it is all related to each other in terms of making power - volumetric efficiency, thermal efficiency, fuel octane ratio, boost level, head porting, valves size, camshaft duration- one big happy family)
Only to the 90%' ers. Most of these test are rather superficial. The main points of lower compression is to run higher boost pressures without exceding about 930C exhaust temperatur and without excessive peak cylinderpressure. Pr. lb/ft and pr. hp lower compression ratio engines has lower peak cylinderpressure but higher BMEP. An honest test would be to put twin turbos on these engines, use pump fuel and boost and tune them to the 930C limit. That would be an eye opner to lots of folks. Nitrous is fine with high compression ratio.
@@chipcurrey653 No problem. 930 degrees C is 1706 F witch is depressingly easily exceded when boosting on pump fuel. We struggle with this all the time and had to develop someting we call "The theoretical NA hp" to keep an eye on things. This engine produces 649 hp Na, 1.20 hp / CID. When boosted to 11 psi it produces 939 hp and that is only 534 hp from "the theoretical NA engine", not even 1.0 hp/CID = junk.
You sold me a 540 power adder because of your 3 boost video!😀😀😀😀😀🇺🇸 Delivery is suppose to be this month! Hoping delivery is soon. Wouldn't a 10-71 be much better with less intake charge heat???
@@richardholdener1727 I went with a intercooler from blower shop Teflon billet 10-71...looks like a very nice teflon frying pan finish on rotors. Much has changed since 1986 using high deck truck blocks stroker cranks weld up jobs...lol. 520 c.i. but with aluminum rods lot of clearance block and rings awesome against big budget teams. My 31 chevy weight wet w/driver 2259 lbs vs most 3300lbs of those days. Let you know how it turns out. Would let you borrow any of my old/new stock but I am in Georgia...shipping would kill...lol. Thank you idea a year ago when couldn't get parts. Did have 11 month delay with BPE but on mock up excellent at the price.
The comparison SHOULD have been between high and low compression versions BOTH under the same boost psi. Low compression ratio (larger total cylinder/combustion chamber volume) allows for a larger volume of air/fuel charge than high compression ratio at the same boost pressure. This is true only under boost and the difference in charge volume increases as boost increases. The opposite is true for NA motors as the extra combustion chamber volume hinders volumetric efficiency.
First, I enjoy your videos and like your lowest common denominator style delivery free of arrogance, it's refeshing. I've subscribed. I'd like to make a suggestion. To truly understand the difference between the two combinations presented, you also should provide the basic tuning settings on each combo when optimized. This leaves me wondering if your NA test and boosted test on your low compression engine was at the same timing and fueling settings. Without that information, power could be anywhere in the range presented...I can easily tune down my 7.88:1 compression centrifugally blown BBF with nothing but spark and lose 100hp. What were the settings? Did you optimize each to the edge of detonation then back it off a few degrees? What is your process? To respond to you about which I think is better, I need to also know what you mean by "better". If "better" means durable, the reason my 7.88:1 combo is what it is is because you CAN NOT detonate it at the limit of the supercharger, even if you have a brain fart and dial in 40deg total advance. It will just stop making power and nose over, it won't ping. I make all my power with flow and leave a ton on the table for safety margin. I don't need more than 1000hp, and I don't care about efficiency.
You can run high compression and power adders you just need to run a better fuel to stop pre detonation and I would think the engine isn’t gonna last as long running higher compression and power adders . But if you can tear it down at home and refresh the engine after a season of racing and run something like alcohol or e85 or something along those lines and just knowing what you’re doing helps alot
I think the right cam probably get you close to giving you The Best of Both Worlds a lot of things that factor into this!" I would have ran 10:1 in the street motor&sent the customer on his way boost is all about cramming as much air fuel mixture into into the cylinder for the biggest pop 8.5:1 on the same gas
what will that do on pump fuel? I dont have access to e85, just water injection. My current LS3 runs 10psi was thinking of making a 10.0:1 CR and doing 15psi on pump fuel?
@Nathan Devine You can still run 15 PSI on pump fuel, I do as well, but you'll have to keep the ignition timing much lower. That isn't great for exhaust gas temps, though. So far, I've been alright. On 93 octane before torque peak (4400-4800 rpm or so), I'm around 15 degrees of timing. At torque peak (5200-ish), I have to drop all the way to 10.5 degrees of advance to keep out of knock. After 5200 rpm, I ramp up to 16 degrees little by little until 6500-6700 rpm. Probably need even colder spark plugs, too. On E85, I'm over 20 degrees, dropping to 20 at torque peak, then back up a little after. It makes a huge difference in power.
@@speedycpu Thanks for the reply i didnt expect one so soon. I have EGT sensors in all cylinders and water injection to keep cylinders cool hopefuly. forget E85 for the moment i only have access to 99ron (UK) so thats probs your 93/94?. im at 10.6 maybe on my LS3 with 10psi and it does 650 at the hubs. I'm building a fully forged 6.0 steel block because i want to do more 20/30min races, it has a custom ECU so i can put in all the safety's i ever need. i want to get about 800 at the hubs but i dont know whether to say stick with 10.5 CR or even 11 and go for say 12/13psi on pump or drop to 10.0 CR and go with 15psi on my maggie 2300 heartbeat thats in my E39 M5 my brain is telling me go with slightly higher CR and lower boost which means less belt issues also and in theory less air heat. whats the most youve run on pump fuel with say meth/water injection or even just pump
@Nathan Devine Personally, I'd go with the higher CR and try the highest boost possible, then ramp timing up until you either hit EGT or detonation limits. You can also run an octane booster, like Boostane, if it is available. The most I've pushed my Procharger and LS3 was to 14 psi, maybe 15 in perfect weather. If you are running a twin screw, you'll likely have a higher chance for detonation at lower rpms, but water/meth can definitely help a lot there. Are you tuning with HP Tuners at the moment? That's what I've been using, but a custom ECU would be awesome. I eventually want to go forged 454 from TexasSpeed and twin turbos, but that will be a while. I need to upgrade my 6L80E because the power it is making now is causing it to slip. I'd say see how it goes with the higher compression. Just keep an eye on detonation and EGT. If that's all good, have fun. Later on, you can run higher octane and get even more out of it. I don't think under 11 CR is all that bad. Guys run a lot of boost with Gen 3 Coyote engines, and they're amazing.
@@speedycpu i have a maxxeccu pro with all the sensors So you dont think that 10.5 with say 13psi on a heartbeat 2300 with fully forged internals is a bad idea? Iowering CR and making it up with more boost is just not my ideal scenario as more boost, more belt slip and less response down the RPM range essentially i could go with 10 and 15psi but im concerned about controlling belt slip with a 2.85 inc pulley
I don't think you NEED to run low compression motors so often anymore. Fuel quality is much better than it used to be. We have quality programmable ignition curves today. And if you have issues with detonation, E85 is likely available, or if not you probably live in a state with 95 or even 98 octane. I ran a L28 with boost happily at 10:1, on CA 91 even! But I had programmable EFI with COP. The factory setup would ping on 7.8:1 if I put 87 in it. Ditch the crappy dizzy and put in proper crank triggered control and so many problems go away. Heck, just the gear lash on the disteibto drive on a worn out shaft can be 4+ degrees. Any motor will ping itself to death with that kind of error window under heavy load.
@Richard Holdner... what's your guess on a 12.6 comp 500" Mopar engine. Flat top pistons for superior burning quality. Good heads, Edlebrock Victor 440s at 380cfm intake 285 exhaust 780 lift. 310 cc runners for great air speed/torque..I have a custom cut 800 lift cam on a 110 LS angle "because of Wedge heads you know"..285 & 292 at .050....when we minus the lash bingo were on point 👍😉 I also modified my tunnel ram to mount my 8-71 blower. Non stripped.. ( Long before fried burger🍔 done it on enginemasters.) Got 2000 CFM of carburetors. I got 12.8 psi an run on M-1. And also run M-5 periodically... big tube headers ,msd ignition. 11 gallon per minute fuel supply. All the bells and whistles. I'm guessing 1300 to1320 HP.. it was around 840hp before the blower and alky set-up... Guys the alcohol and blowers ( any forced induction) are a match made in Heaven💯... inlet air temp is crazy even on a hot summer day.😉👍. Nobody seems to wanna try a Dragster on the chassis dynos. 😕 So I just go by weight and ET for my guess regarding HP
@@richardholdener1727 well at 12 + psi. We obviously got the flow haven't we ? It pulls 7300rpm... & 4.78 1/8 th. 148 to 151 mph. I'm just curious bossman. Thanks for responding Richard 👍😉
With my 427 LS with an F1-A, I built it to 9.65:1 as there is not 1 E85 pump in my state. My combination with the blower maxed out makes 12lbs of boost, if I would have known this in advance I probably would have built it to 10.65:1.
WHAT IS THE BEST COMPRESSION FOR BOOST? Great question! WE HAVE ALL BEEN TOLD THAT WE NEED LOW COMPRESSION WHEN BUILDING POWER ADDER (SUPERCHARGED, NITROUS AND TURBOCHARGED) MOTORS, BUT IS THAT STILL TRUE? Even better question! Unfortunately, this test shed no light on the answers to either question. If you put the same power adder on the 10:1 engine, would that require subtracting enough ignition advance to erase the 50hp head start?
I went with middle of the road 9.5 to 1 with my turbo coyote motor for longevity and forgiveness. I know the stock compression ratio is higher and guys boost them but they're not out there every weekend at 7500rpm either.
I like lower static compression simply due to the reduced fuel cost. That's the biggest long term expense for someone that actually drives their pile on the street, after all. 87 octane, all day every day.
@@taylorsrus9543 Because it's still a 540 cube engine. No reason why you can't run some 112 in it at the track. No reason to need 98 when you're on the street. Just add more nitrous or turn up the boost another pound or three.
I believe we have reached the next plateau in internal combustion engines. Now the parts are stronger can we get the cooling and lubrication systems to meet these higher demands???
Compression is great for power and if you have detonation issues add a camshaft with overlap to help I like compression with less boost then lower compression high boost
if you have e85 avaiable i see no reason to run at 8.5:1, a roots blown pump gas street deal, the lower compression might be good, gets hot low quality fuel hot day ect. iv been running a blower on 9.5:1 cr 8lbs of boost with e85 for years im pretty sure if i turned it up higher i would find the horsepower limit of my rotating assembly before id run into detonation.
Time and place for everything. I feel like fuel and ignition control technology has come so far that the low compression boost rule of thumb has gone out the window, especially considering fuels like e85 with such a cool burn are widely available. I have an 11:1 ls that was a max effort n/a setup that now has a 78/75 on it and I don’t have a care in the world even on 93- I put a terminator on it and I tell it what to do, if it never sees big timing at high boost and it always hits my pig rich target afr it’ll live for a while. However, I still have my first car with a tpi (well, stealth ram) and a 7730 sd ecm which I refuse to change. I have an fmu and a 6btm box- that setup isn’t controllable enough for me to be comfortable tossing a ton of compression at it. So I guess there’s no end all be all answer other than “you can get away with it if you really want to”
If you’re running two turbos individually ( non compound) I would think that 10.5:1 cr would work well with 13 lbs-14 boost with a 245@.050 .600 lift roller compression. Am I correct? I want to build a 416 ci engine with a 1000 hp at 6000 rpm peak. It is an FE. I would think that it would be a streetable E85 engine.
On a street or track car Low compression is not necessary nor is it beneficial with modern engines and tuning components. Now if you are using old school tech YMMV, but with newer engines and newer ECU systems we have enough control and good enough fuel available to run wild compression with boost and this is beneficial for a number of reasons.
Me with my turbo ls1 (i know different style engine/configuration) I've almost finished building it, i like my comp around 11:1 with boost and race E85 , yes gives you some safety margin and the comp will give me decent torque down low and won't be a absolute pig with no throttle response etc when not really on much boost..So yeah definitely comp for me 💪
I don’t play with old v8 stuff. But on my 4g63 I run 10:1 and any e85 only car I build the motors 10:1. Motor has seen 47psi from a 67mm turbo and 788whp. E85 is amazing stuff. Performance is on par with c16.
My ls 6.0 was told to go 9.5:1 with E85 and over 15 psi boost 1200 hp. Now if I switch to methanol do I need to change anything compression, ring gap, bore hone, I am unable to find anything related. Maybe a Q&A on switching fuels.
Diesel motors are very high compression for ignition and they run boost no problem. Like you've said many times, boost is just a measurement of inlet restriction. I'd love to know the difference between 10 to 1 comp and 8.5 to 1 comp making the same power irrelevant of boost, what is their peak cylinder pressure? Is there a difference? And if so, does the temperature change? Does this change volumetric efficiency? I think there is a sweet spot, and the rules/ guidelines change depending on the fuel being used. And thus can drastically change the output and behaviour of an engine. I feel there is probably the point of diminishing returns also - will have to wait and see you test some more!
I thought we were going see what the blower on the 10 to 1 motor did.
Yeah wtf lol
lol i was thinking the same thing! i rewound and watched back to see if i missed the numbers somewhere lol
Ditto. I was expecting to see what power it made in the 4-6# boost range... maybe one more pull at 8-9.
Rich prob didn't do it bc he knew what was prob going to happen! ;)
@@nabilguffey3201 No way he could have run the same blower speed on the higher compression motor with the same fuel. Less boost, less power.
I don't think this comparison is terribly helpful. The question I think we're all wanting answered is: if you're OCTANE LIMITED, say building a pump gas motor, which is a better approach, low-compression/high-boost, or higher-compression/low-boost.
Even if your octane limited you can always pull timing out to keep.it happy with the higher compression.
@@chadcollyer4957 yeah, but will you pull so much, you would have made more power from the low compression engine?
@@chadcollyer4957 to a point.
all of you are wanting?
get a 9:5.1 compression, high compression will develop knock eventually if a mistake is made, then you need a rebuild, plus you'll always need high octane gas, no exceptions.. High compression is like having a gf who is only happy when you kiss her ass, the day you don't, she dumps you n you're stuck with pink eye..lol
The issue we had back in the day with high static CR's was timing, the quality of the head gaskets and the carb technology. Today, you can pull timing out of the motor exactly where you want it, tunable closed loop MPI with knock sensors and MLS head gaskets, so yes, I feel you can run higher static ratio's and pick up torque down in the lower RPM band, especially with turbo's.
Ethanol baby!
and aluminum heads help reduce the tendency to detonate as well as offer better shaped combustion chambers.
@@albertgaspar627 Yeah, I'm doing a Saturn 1.9 LDOHC build on mine with 10 to1 comp with low boost 8-10 PSI and an E85 blend. Building the most velocity instead of volume, JE forged pistons, ARP main and head studs, knife edged 3rd gen crank and lower tie plate, port and polished head, mild intake deshrouding, mild bowl blending, dual intake cams, ported polished intake manifold, bigger TBI and low boost E85 like I mentioned.I figure it'll be better if the machine shop builds it well. The car is light with the polymer panels, carbon fiber hood from Seibon, and the 15X7 Einkei RPF1's that are 9.8LBS each, and Mfactory limited slip differential. Should be a fun ride to surprise some people as well with my little baby car, ha ha...lol My engine is light too at 220 LBS, half the weight almost of a normal 4 banger from the lost foam casting..lol
@@junechris sounds like a nice design, check out David Vizard's channel too. he does dyno work with headers, you might find some tech there to help the velocity you want by clearing out the combustion chamber as fast as you want to fill it in. As you know, the joy of DOHC is you can play around with overlap and lobe separation by moving the individual cams around instead of having to buy a new re-grind.
I have a naturally aspired GM EcoTec 2.2 litre in the "pile" of project cars, would love to play with its potential since GM already went ahead and had a supercharged version (like the Saturn Ion). As you know, in a light car it can be a sweet piece when done right.
@@albertgaspar627 Yeah, I've heard about the cam options you mentioned about. Right before u messaged me, I was happy to find Ross makes forged pistons right in their catalog for the Saturns. And one of the other guys I spoke to on here was a 30+ year machinist that seems quite fond of the Ross ones in regard to the ring gap recommendations being more or less right on the money so i'm gonna relay that to my friend doing the build for me tomorrow.
Richard I think you're videos are fantastic my only issue is you rarely use pump fuel i understand the limitations and possible engine damage when testing but I think its what a large percentage of viewers run. I would love to see more of it. The power you get on hi octane would be unobtainable for a lot of us.
The only reason to run lower compression in my mind is if you don't have access to quality high octane fuels. Otherwise, more compression, the better, assuming you can time it/tune it correctly
Even in that situation you can always pull timing out to keep it happy with high compression.
This is exactly my issue
@@chadcollyer4957 until you run out of timing Dx what I'm dealing with.
Higher SC and TC MAP.
Even then that's what AEM's meth kits are for. $700 for their biggest kit and $2 a bottle for winter washer fluid.
Before even watching it I know the high compression one will make more power with boost because boost just enhances the NA curve of that engine. The better NA the better with boost.
You said it, the roots application is probably best off with the 8.5:1 long block. By my rough calculation, the 11 psi boost would have given you well over 1100 hp if not for the power needed to spin the blower, about 195 hp if the formula held true. That’s basically lots of heat added to the intake charge. If I had a couple GT-45s making that same 11 psi, I’d want the 10:1 or even more, EFI, and E85, too! That 540 would be a beast either way, I think.
If one wants to run high rpm and 30-40 psi boost, then 9:1 would be as low as I would ever go... Tuning becomes critical with higher compression, but will always make more power, and efficiency on daily drivers... The way the compression is made is also important, like having a dome piston with it down in the hole 60 thou would be asking for detonation and/or pre-ignition. Proper design combustion chamber is imperative for the proper platform.
I like stock compression + ring gap + boost because well, pistons are expensive and junkyard engines are cheap!
For running on pump gas, I think it makes a difference how much boost you can run without running into detonation. The dynamic compression ratio based on cam specs is a big factor, too. Even though the static compression may be 10:1, the dynamic compression may be a lot lower with a big cam, so lots of variables there, tough to do a true apples to apples. Good stuff to talk about, though!
Higher compression with boost increases the likelihood of detonation. Lower compression gives more wiggle room to withstand that issue. If the tuning is spot on and the fuel has really high octane (91+), then the higher compression will not cause an issue. Lower compression is often recommended for boosted engines because it just allows for more error.
Imo for street usage lower CR sounds nice to run regular pump gas. Go on the track and pump up the boost with better gas.
If you have race gas, high compression and high boost is best. Lol
Even on pump gas I think the higher compression would be better. Off boost performance would be better and if you are tuning for maximum power for a given fuel the maximum output should be the same because the cylinder pressure where knock occurs would be the same.
@@christianmeeks4430 pump gas and high compression means your ignition system and timing needs to be dead on lol
@@rcairforceone the difference is that "dead on" is much more attainable today than it was in 1990, let alone 1980.
High compression vs low compression. High compression runs better out of boost.. but runs the same in boost but with a smaller tuning window.
Also, having Richard Holdener making motor sounds when your motor is under load is worth a few more octane points
I think this is an excellent question. Most people are going to be limited by the fuel octane availability, and I also dont see anyone else providing any data on this subject.
Man, this is a timely video. I am looking at these exact motors and wondering the same things discussed here. Thanks Richard for the comparisons.
The noise you made for each engine at the beginning made my day! Well done sir! 👏
To answer the CR question just look at diesel tractor pulling. They use lower CR pistons so that more boost can be put into the engine. So yes, depending on the extra air to be added, lower static compression can be a benefit.
Absolutely, I run 8.5 CR in a LS stroker and it allows me to run way more boost than if I was at 11.5 CR. Plus the fact I don't have to worry about detonation.
the test that needed to be done would be to boost the both motors to the same cylinder pressure at TDC, the lower compression motor motor is in theory larger then. All compression done in the motor creates heat in the charge, compression done outside the motor with boost and intercoolers, results in more mass flow rate.
Thats why I watched the video. I thought he tested both combinations. I am kind of pissed he didn't.
Finally some quality content coming across my notifications…
Modern engineers have things figured out by now and technology only gets better. It's easy to see what compression ratios are "safe" for a boosted engine by looking at modern flagship cars like the dodge demon, GT500, and ZL1. All posses compression ratios from 9.1-10. can forged and aftermarket engine components survive more abuse. Possibly, but many guys are fooled into thinking their engine has some magical abilities because it continues to live on a certain static compression ratio and boost level when in reality many times the engine has a cam with great overlap (lowering dynamic compression) or the engine has quality components and is just suffering through it. Another mistake is people think that any boost level on a said compression can be attained by lowering timing. In reality, an engine that creates knock from a product of heat due to the combined boost and compression ratio gives no attention to when the spark plug is told to ignite. This is why it's called pre-ignition.
Interesting
I think the question is what the goal is. Absolute max power? Low CR and lots of boost wins. More return on boost than CR. Driveability with a flatter curve without spikey boost curves? Higher CR and slightly less PSI from the whistle bits.
From my experiences with low compression motors, they do an excellent job in colder places. Ohio, Minnesota etc. Low compression motors are amazing for torque gains. Gives you a different feeling when you put your foot on the pedal.
I've seen the exact opposite. The high CR starts easier and makes more Tq overall.
You CAN run a high boost on a high compression engine, IF!!! you have an inter-cooler. The problem with a super charger on a high compression engine, is temperature rise during compression. Too much compression could mean reaching temperatures high enough, for fuel to "auto-ignite", much like a diesel engine. The fuel may not wait for the spark. That pre ignition will destroy the engine. If you're going to boost, without inter-cooling, lower compression is a MUST! No matter what, I do recommend a high octane fuel on a boosted engine, because of its higher ignition temperature.
You can but, what's going to produce more power?
I would never consider 8.5:1 with that cam size and a limit of 11 psi. Flat torque curves are what win races and generate efficiency on the streets, not peak numbers. I once watched a video of BMW m7, 770hp 4.4 v8 outrun a late model Dodge Challenger at 1100 hp w/ blower from a 60 mph drag. 1100 hp is nothing to cough at, but the Bimmer just ate his lunch.
Personally, I am about efficiency, and it is more about building what works than cool dyno digits. That's how I got an 11,000lb dually 5.9 Cummins to outrun an Audi A6, on a 62mm turbo, w/o melting down...
And with 300k mi on the clock...
When you factor in limited octane, it comes down to the detonation limit of the compressed charge. 8.5 to 1 at 14lb of boost will have 250psi compressed where 10 to 1 will have that same compression pressure at 10lb of boost. the difference is the lower compression engine will have a larger combustion chamber with a larger charge at the same pressure. obviously at the same boost the more efficient higher compression ratio will make more power. But that only works with fuel that will tolerate it. Run the same engine on pump gas boosted to the detonation limit and I think the lower compression combo will come out on top.
I have recently taken a low boost paxton motor that was 8:5:1 to 11:1 in a corvette. I left 100hp on table for years by not running higher compression. Motor runs better, idles better, all drivability better. BUT it is compensated on boost by methanol injection … however it was at 8:5:1 also. So was winning combo foe me
Lower compression would be good in a drag week application to run pump gas on the street. I like E85 but no telling what availability would be on rou te. I would probably go 9:1-9.5:1. As you've proven Richie.....more efficient n/a the better the power will be boosted.
yeah i agree too, going too high in compression will eventually develop "knock" no matter what on a boosted application, n that's the reason many ppl end up selling their "builds"..lol i rather have a nice 9:5.1 compression as i have in my 2v n run pump gas or e85 n be good on boost..
The advantage of high compression with boost is the reduced effects of boost lag. The advantage of lower compression is you can run higher boost levels before grenading the engine. I think a low compression engine with the same components will live longer with high boost pressures.
Through my years I've found you will make more power on a higher compression engine. A lower compression engine really shines at very high boost 35psi + and large spark advance. You will detonate a higher compression engine allot easier. I would rather have low compression and high boost then higher compression and low boost.
Pump 91/93= lower compression. No lower than 9 to 1 tho.
E85= all of it.
i'd take the 8.5 for longevity alone, but i'm not a competitor.
and considering the price per gallon of 93 octane, that 540's gonna gulp down the gallons. buy the cheaper gas, still have 600 + hp
If your hard parts can handle the stress the higher compression version will always make more power.
Agreed with proper fuel
All my best performing boosted 4 cylinders are 10.1 or more compression with good flowing cylinder heads ! E85 is key to keeping them alive
Be interesting to see a comparison between these 2 for a pump gas application where the octane would more than likely be the limiting factor
I totally agree with you, they both have their place. You just have to build what it is you are building for. In a W.A. Street Machine, I'd run low CR for the "just in case" factor.
W.A?
In a boat with crappy gas docs - no, in boat with severe load all the time - no, with out fresh water cooling - would help things , another aluminum head justification - IE 1 point of compression as a gift - I went with a roots from mooneyham for the sound and nostalgia and 8.8 - 1 with ICON pistons
If your concerned about drivability low compression higher boost on premium gas or e85. if drivability isn't a concerned and you're more all-out drag racing or weekend warrior you want higher compression racing fuel like e85 c16 C32 or methanol to control predetonation with high boost. You either have low compression 14 lb of boost premium fuel for E85 and get 1000 horsepower or high compression racing fuel or methanol had 7 pounds of boost and get 1000 horsepower. my opinion. P.s boost and hp numbers is just an example
An actual true comparison is to have two Motors that are built the same with every part the same the only difference would be is ring Gap and compression ratio. but video has good information.
If you trailer your car to the track, yeah, go for the compression, because it's not gonna get hot enough. For a street car, choosing the lower compression offers your a better portfolio of benefits with boost. That said, 8.5 may not be necessary. 9.0-9.5 is fine with a big cam.
The 8 5 to 1 would last a lot longer due to the lower compression ratio,and you could run it a tad fat on E85 and drop the oil a 10K or 5K,be an easy one to love
No reason to run compression that low with e85. I’m using 10.6 to 1 static with 20 psi from a Procharger on e85. Been 4 years without issue.
Low CR is dinosaur inefficiency. Engine control systems and engine design in 2022 do not require low CR for boost.
I read an article that claimed higher compression in a boosted engine would tend to fight against itself… as the RPM increased, the pressure in the cylinders would also, thus keeping them from operating at their max n/a rev capability. Think of how hard it becomes to pump more air into a bicycle tire when it’s close to it’s rated psi. Maybe this inverse relationship explains why top fuel cars run such way low compression; they need the RPMs at the top end. 0:08
they run low compression to allow volume for more nitro fuel
The book I recall reading - mid-late seventies era; I think the title was something like “super power” - spoke of 20% *underdrive* and 8 to 1 compression when running a Roots blower. (For routine-level street use, I think.)
The shop that built the 4.3L for my Typhoon bumped up the compression to 8.7:1 but they also built it to handle 30psi.
As always great content...
Haven’t seen you in a while, Hope all is well..
Really bummed you didn’t run the Higher compression motor with Boost?
I think everyone was expecting that.
Just Say’n
As always great videos.
Again, truly hope all is well with the family, etc...
the 10:1 wasn't mine-but we can guess what happens by now...right?
Not sure what Happens Now?
I do know quite a few mustangs running stock compression with Boost as well as LT1’s
Higher CR always makes more power but you're limited by the Detonation resistance of Fuel used. Boost increases the need for higher detonation resistance.
High CR with boost is a very powerful combination, especially turbo as it spools much faster than a low CR motor
That's what meth is for.
I'm running 11.3:1 compression
E85 and 5 lbs of boost
With the cam I'm using
My effected compression is 15.47:1
I've done a few things to help
Heat coated tops and dry lube on skirts Total seal gappless second ring gapped at .028 4.31 bore 4.25 stroke 496ci AFR heads with mirror polished combustion chambers.
I don't have any problems
I like the lower compression because it is more forgiving. More power is always better, until you break something because it's temperamental.
This might be more applicable to those of us with small cubes. One of the cool things about high compression is that it makes more power off boost. Makes for a car that's fun to drive on the street out of boost. Yeah, a low compression 454 is going to be fine around town, but think about a 2.0L.
I run 11.5 CR with 11 psi of roots blower boost. You can have both boost and compression. I do run water/meth injection to keep it safe when circuit lapping though. Which bypasses the need for E85 which is not very available in my part of the world. Can run in on straight 98 (RON) pump fuel though, no problems, just that it will start to pull timing as air intake gets hot.
Build a grand national 3.8! I made 730rwhp with a 76mm precision and hogged out iron heads. Then with a set of champion aluminum heads and a bump up to 4.1L, I made 1,032 rwhp with a/c and went 8.89@164 back in 2000. But we Buick people need some love
What fuel were You running?
C16 on high boost, 38-41psi and sunoco 98 for street driving. I was also working for VP fuels at the time
38-41 psi sounds crazy. What psi for "street driving"?
Back in the day it was 3 things, 1 fuel. Didn't have e85 at the pump, 2 didnt have computer software that could control things properly. 3 we didn't have you Richard.
well, 2 out of 3
It would be fine on 10:1 as long as the pistons gave top ring located lower than typical on NA. Considering other factors arectaken care of. The only way to truly test this is back to back on the same engine. Either swap pustons only, or swap heads as long as heads are exactly the same except combustion chamber size....
I’ve ran 9.25 :1 on 6 to 8 psi in a marine application , the problem is the load that exist in a boat to put that into perspective have you seen a brake pedal in a boat ? But we also have the biggest radiator there is that being lake water , so cool engine temps say 140 to 160 combined with aluminum heads , coated pistons , allows us to get away with a lil higher compression, but 10:1 in a marine app I mean I’d doit but wouldn’t recommend it to a customer
Yes on low compression for a blower motor on pump gas.
I’m going low compression on this one. Can’t see the 50 horse being worth the security the lower compression offers. Especially being able to make up the difference with more boost. And because I am a budget guy who is remarkably impatient… I’d also probably run it before I got the blower or turbos and just beat on that thing while running lawnmower gas and have a blast.
Most of us also aren’t running 540 ci for an LS1 or something it’s probably an even smaller gap like 30 horsepower
IT'S 3-4% OF NA POWER PER 1 POINT
I was told to go with lower compression, and I was told a supercharger raises static compression. Moroever, for a lot of boost. I was told to consider alcohol, but I rather run pump gas 91 octane, so I was told not to run too much boost for a supercharger roots style application. I am curious what you think.
supercharger has no effect on static compression. Pump gas and low compression are a good match with a roots blower
A missing element in your test: the cylinders exchange the same vol of air NA. Not so on boost. As a result, can you run more boost on the PA motor while achieving the SAME dynamic compression or peak cylinder pressures? It stands to reason you can. The net effect of using boost may be the larger compression volume of the PA motor would effectively act like a larger displacement and has the potential to make more power at the same peak cylinder pressures.
Higher static compression just requires less boost for the same power. This is why my LSA motor is 11:1 static. I don't have to spin the blower above its max efficiency to make the number I need...
4500 flanges offer better cylinder-to-cylinder distribution and a little straighter path down the intake runners over an equivalent 4150 intake, right?
Let's be honest, fuel quality(and, later, emissions) is what has driven compression ratios since the earliest engines, and, today, fuel quality is as good as it's ever been. A better NA engine is a better power adder engine all said and done, it's better off of the power adder(minimal boost or not spraying it) and it's better on the power adder.
This essentially goes back to "should you build your boosted engine, or just increase the boost?" - at the end of the day, 1000HP is still 1000HP, and an appropriate torque converter & gearing can band-aid any power curve(I mean, if they can make 1000lb-ft@1500RPM diesels work... Lol), so this may not be particularly relevant to the junkyard LS + Amazon turbo crowd - but, if you're building an engine, you're going to have to give me a hell of a reason why not to go high comp. There's applications where you want the greater safety margin from detonation for sure, but fuel quality is so good today, nevermind the availability of an alcohol fuel at the pump(E85), that the risk has fallen. It wasn't that long ago that everyone thought these Coyotes were going to be blowing up with boost because of their 11:1 stock compression - so much for that theory LOL.
Maybe I'm biased though, we've been spec'ing out an engine build for my nephew's Mustang and, having grown up with the Modular scene, I was influenced by high comp + boost earlier. Needless to say, right from the beginning we've been planning on ~14:1 comp with softened chambers, and moderate boost in the future. Probably a 438" Windsor, probably high ports, and probably a Holley Hi-ram, controlled by a Terminator X... ...but nothing is set in stone until the money is spent of course, but we've already started with the TermX.
Oh yea, and for an E85 'street car' of course lol
I think you hit the nail right on the head. I think back to how many bone stock LS2’s were running around with 10+ psi of boost on daily driven vehicles. Mostly Corvettes. 11:1 CR and stock ring gaps. That was before E85 was super popular too.
The size of the booster can determine lower compression but cam crutching is the key.
I run 10:1 compression on my 429SBC with 26 pounds of boost from an F2 Procharger on E85. Runs great in my street car.
For the street on pump gas low compression for the win. Easier to control detonation.
Why though would you recommend low compression for boat motors at wide open throttle say on E85? Is it the extra heat from the higher compression motor that causes problems????
As I understand it, it really comes down to engine management; that an ECU can figure out cylinder conditions by running a very, very low power signal through the plugs when not triggering combustion, absolutely blows my mind. At that point, it comes down to the better thermal efficiency of the higher compression, provided you can still run your desired boost/airflow without pre-detonation
low power signal through the plugs?
@@richardholdener1727 yes - I can't find it now on a Google search so I wonder if I have a misunderstanding - a couple years ago, I read in my dad's Automotive Engineering that the high-end (read: German/Euro & Japanese) brands are using spark plugs to get a better idea of combustion chamber chemistry (because the impedance changes relative to air density and chemical composition). He recalls the tech as well, so chances are that I'm not crazy or making this up
Point being....his Audi has an 11.5:1 CR turbo 4-banger. Engine management is changing what a "safe" CR for a boosted application is
I searched, "using spark plug as a sensor"
I was hoping to see the same blower put on the higher cr motor but driven slower to make the same power as the highly boosted low cr motor and than figure out witch way was better.
This is only theoretical, but I think more compression and less boost would heat the incoming air less, while creating equal cylinder pressure. Thus MAYBE the air would denser. Sure, there's intercoolers, but that's more expense.
I'm just here for the awesome engine sounds
I can't see a high compression boosted engine being able to withstand the same octane fuel as a low compression engine with both running the same level of boost. The lower compression version could run more boost than the high compression and overcome the lower compression shortfall.
It all comes down to fuel choice and timing. The theory hasn't changed. You cant run high comp with high boost for pump fuel. e85 is a different story as already mentioned in the comments.
Good video
If the engine is not in a race only (or boat) application where a certain amount of practicality goes out the window, higher compression is the way to go, you'll make more power for a given amount of fuel, so the fuel system can be smaller and you don't have to stop at the pump as often. You will also make more power off boost which will make the thing easier/nicer to drive in a few different ways; it can compensate (a bit) for a wilder cam at low engine speeds making any low speed driving much nicer, it also means you might be able to shave a few 100 rpm off your stall on your torque converter.
Modern ECUs can do closed loop boost control, knock retard, IAT retard, exhaust backpressure retard and table blending based on ethanol content; people are talking about driving on pump gas and lower comp being better, but really all you would need to do is either change map with slightly lower boost and less timing, or do nothing and let the ecu pull timing if your ECU is tuned correctly.
Not exactly. Knock sensors are not exactly scientific level sensors and some setups can suffer catastrophic damage almost instantly if they encounter detonation. It takes a dyno and good tuner to find that line in the sand. You add tiny amounts of timing until the motor no longer produces increased output. Then you back it off, to each tuners opinion, on what they feel is adequate safety margin...
For a race engine there's no need for low compression I see dudes running 13to1 with turbos but if it's a street car then lower compression would allow you to drive it on normal gas you just wouldn't be able to really beat on it with the normal gas.
The higher the compression the lower the Boost. I want to try 12.5:1 at 4-8lb of boost in a LS3 or K24/20 head. Twin Garrett 3776's or single Garrett 3776 for the K, electronic wastegate. Start at 1lb. and work up to the max. I'd stop at 8lb. even if it took it like a champ. 4 boost settings, 2lb. 4lb. 6lb and 8lb.
What I want to see is a 13-1 compression with low boost
All depends on the fuel... In a boat buying premium pump gas at the fuel dock, I'd want the 8.5 motor. If I could reliably get decent E-85, the 10 motor would be OK.
But we only have one E-85 pump in the whole county ... And no-one can afford race gas on the street, out cruisin ...
Richard, I think you need to read a goid article in DC Sport magazine that explains very well what CR is the best for your application. Basically higher CR shines up to 2 Bar of boost. After that point lower CR takes over. You need to taje a look at their table which represents both - volumetric efficiency and thermal efficiency. For instance in my forced induction application with 3 Bar of boost I use 8.5 CR. Had I used 2 Bar of boost or less I would've raised CR up to 10.
Thnx-I understand thermal and volumetric efficiency and the trade offs-they exist in NA motors as well-which is why continued increases in static compression don't continue to yield a strict % change in power
Yes, as you well know it is all related to each other in terms of making power - volumetric efficiency, thermal efficiency, fuel octane ratio, boost level, head porting, valves size, camshaft duration- one big happy family)
What fuel will it be running is the biggest factor in my opinion.
The man to singlehandedly end all forums arguments
Only to the 90%' ers. Most of these test are rather superficial. The main points of lower compression is to run higher boost pressures without exceding about 930C exhaust temperatur and without excessive peak cylinderpressure.
Pr. lb/ft and pr. hp lower compression ratio engines has lower peak cylinderpressure but higher BMEP.
An honest test would be to put twin turbos on these engines, use pump fuel and boost and tune them to the 930C limit.
That would be an eye opner to lots of folks. Nitrous is fine with high compression ratio.
@@finnroen2334 Sorry I'm too free to speak metric.
@@chipcurrey653 No problem. 930 degrees C is 1706 F witch is depressingly easily exceded when boosting on pump fuel. We struggle with this all the time and had to develop someting we call "The theoretical NA hp" to keep an eye on things. This engine produces 649 hp Na, 1.20 hp / CID. When boosted to 11 psi it produces 939 hp and that is only 534 hp from "the theoretical NA engine", not even 1.0 hp/CID = junk.
You sold me a 540 power adder because of your 3 boost video!😀😀😀😀😀🇺🇸 Delivery is suppose to be this month! Hoping delivery is soon. Wouldn't a 10-71 be much better with less intake charge heat???
the intake charge won't be much different-just the max power potential
@@richardholdener1727 I went with a intercooler from blower shop Teflon billet 10-71...looks like a very nice teflon frying pan finish on rotors. Much has changed since 1986 using high deck truck blocks stroker cranks weld up jobs...lol. 520 c.i. but with aluminum rods lot of clearance block and rings awesome against big budget teams. My 31 chevy weight wet w/driver 2259 lbs vs most 3300lbs of those days. Let you know how it turns out. Would let you borrow any of my old/new stock but I am in Georgia...shipping would kill...lol. Thank you idea a year ago when couldn't get parts. Did have 11 month delay with BPE but on mock up excellent at the price.
The comparison SHOULD have been between high and low compression versions BOTH under the same boost psi.
Low compression ratio (larger total cylinder/combustion chamber volume) allows for a larger volume of air/fuel charge than high compression ratio at the same boost pressure. This is true only under boost and the difference in charge volume increases as boost increases. The opposite is true for NA motors as the extra combustion chamber volume hinders volumetric efficiency.
larger volume of AF?
Cylinder pressure is cylinder pressure right
First, I enjoy your videos and like your lowest common denominator style delivery free of arrogance, it's refeshing. I've subscribed. I'd like to make a suggestion. To truly understand the difference between the two combinations presented, you also should provide the basic tuning settings on each combo when optimized. This leaves me wondering if your NA test and boosted test on your low compression engine was at the same timing and fueling settings. Without that information, power could be anywhere in the range presented...I can easily tune down my 7.88:1 compression centrifugally blown BBF with nothing but spark and lose 100hp. What were the settings? Did you optimize each to the edge of detonation then back it off a few degrees? What is your process?
To respond to you about which I think is better, I need to also know what you mean by "better". If "better" means durable, the reason my 7.88:1 combo is what it is is because you CAN NOT detonate it at the limit of the supercharger, even if you have a brain fart and dial in 40deg total advance. It will just stop making power and nose over, it won't ping. I make all my power with flow and leave a ton on the table for safety margin. I don't need more than 1000hp, and I don't care about efficiency.
na and boosted timing values the same? no
Lower compression will give the ability to run less power if you need to take alot of power out.
You can run high compression and power adders you just need to run a better fuel to stop pre detonation and I would think the engine isn’t gonna last as long running higher compression and power adders . But if you can tear it down at home and refresh the engine after a season of racing and run something like alcohol or e85 or something along those lines and just knowing what you’re doing helps alot
I think the right cam probably get you close to giving you The Best of Both Worlds a lot of things that factor into this!" I would have ran 10:1 in the street motor&sent the customer on his way boost is all about cramming as much air fuel mixture into into the cylinder for the biggest pop 8.5:1 on the same gas
10.7:1 on my LS3 at 14 PSI, 20 degrees of timing on E85. It rips pretty good in a Corvette.
what will that do on pump fuel? I dont have access to e85, just water injection. My current LS3 runs 10psi was thinking of making a 10.0:1 CR and doing 15psi on pump fuel?
@Nathan Devine You can still run 15 PSI on pump fuel, I do as well, but you'll have to keep the ignition timing much lower. That isn't great for exhaust gas temps, though. So far, I've been alright. On 93 octane before torque peak (4400-4800 rpm or so), I'm around 15 degrees of timing. At torque peak (5200-ish), I have to drop all the way to 10.5 degrees of advance to keep out of knock. After 5200 rpm, I ramp up to 16 degrees little by little until 6500-6700 rpm. Probably need even colder spark plugs, too. On E85, I'm over 20 degrees, dropping to 20 at torque peak, then back up a little after. It makes a huge difference in power.
@@speedycpu Thanks for the reply i didnt expect one so soon. I have EGT sensors in all cylinders and water injection to keep cylinders cool hopefuly.
forget E85 for the moment i only have access to 99ron (UK) so thats probs your 93/94?. im at 10.6 maybe on my LS3 with 10psi and it does 650 at the hubs. I'm building a fully forged 6.0 steel block because i want to do more 20/30min races, it has a custom ECU so i can put in all the safety's i ever need.
i want to get about 800 at the hubs but i dont know whether to say stick with 10.5 CR or even 11 and go for say 12/13psi on pump or drop to 10.0 CR and go with 15psi on my maggie 2300 heartbeat thats in my E39 M5
my brain is telling me go with slightly higher CR and lower boost which means less belt issues also and in theory less air heat.
whats the most youve run on pump fuel with say meth/water injection or even just pump
@Nathan Devine Personally, I'd go with the higher CR and try the highest boost possible, then ramp timing up until you either hit EGT or detonation limits. You can also run an octane booster, like Boostane, if it is available. The most I've pushed my Procharger and LS3 was to 14 psi, maybe 15 in perfect weather. If you are running a twin screw, you'll likely have a higher chance for detonation at lower rpms, but water/meth can definitely help a lot there. Are you tuning with HP Tuners at the moment? That's what I've been using, but a custom ECU would be awesome. I eventually want to go forged 454 from TexasSpeed and twin turbos, but that will be a while. I need to upgrade my 6L80E because the power it is making now is causing it to slip.
I'd say see how it goes with the higher compression. Just keep an eye on detonation and EGT. If that's all good, have fun. Later on, you can run higher octane and get even more out of it. I don't think under 11 CR is all that bad. Guys run a lot of boost with Gen 3 Coyote engines, and they're amazing.
@@speedycpu i have a maxxeccu pro with all the sensors
So you dont think that 10.5 with say 13psi on a heartbeat 2300 with fully forged internals is a bad idea? Iowering CR and making it up with more boost is just not my ideal scenario as more boost, more belt slip and less response down the RPM range essentially
i could go with 10 and 15psi but im concerned about controlling belt slip with a 2.85 inc pulley
I don't think you NEED to run low compression motors so often anymore. Fuel quality is much better than it used to be. We have quality programmable ignition curves today. And if you have issues with detonation, E85 is likely available, or if not you probably live in a state with 95 or even 98 octane.
I ran a L28 with boost happily at 10:1, on CA 91 even! But I had programmable EFI with COP. The factory setup would ping on 7.8:1 if I put 87 in it. Ditch the crappy dizzy and put in proper crank triggered control and so many problems go away. Heck, just the gear lash on the disteibto drive on a worn out shaft can be 4+ degrees. Any motor will ping itself to death with that kind of error window under heavy load.
@Richard Holdner... what's your guess on a 12.6 comp 500" Mopar engine. Flat top pistons for superior burning quality. Good heads, Edlebrock Victor 440s at 380cfm intake 285 exhaust 780 lift. 310 cc runners for great air speed/torque..I have a custom cut 800 lift cam on a 110 LS angle "because of Wedge heads you know"..285 & 292 at .050....when we minus the lash bingo were on point 👍😉 I also modified my tunnel ram to mount my 8-71 blower. Non stripped.. ( Long before fried burger🍔 done it on enginemasters.) Got 2000 CFM of carburetors. I got 12.8 psi an run on M-1. And also run M-5 periodically... big tube headers ,msd ignition. 11 gallon per minute fuel supply. All the bells and whistles. I'm guessing 1300 to1320 HP.. it was around 840hp before the blower and alky set-up... Guys the alcohol and blowers ( any forced induction) are a match made in Heaven💯... inlet air temp is crazy even on a hot summer day.😉👍. Nobody seems to wanna try a Dragster on the chassis dynos. 😕 So I just go by weight and ET for my guess regarding HP
the max power output will be determined by the flow capacity of the blower
@@richardholdener1727 well at 12 + psi. We obviously got the flow haven't we ? It pulls 7300rpm... & 4.78 1/8 th. 148 to 151 mph. I'm just curious bossman. Thanks for responding Richard 👍😉
With my 427 LS with an F1-A, I built it to 9.65:1 as there is not 1 E85 pump in my state. My combination with the blower maxed out makes 12lbs of boost, if I would have known this in advance I probably would have built it to 10.65:1.
Great Information Rich
WHAT IS THE BEST COMPRESSION FOR BOOST?
Great question!
WE HAVE ALL BEEN TOLD THAT WE NEED LOW COMPRESSION WHEN BUILDING POWER ADDER (SUPERCHARGED, NITROUS AND TURBOCHARGED) MOTORS, BUT IS THAT STILL TRUE?
Even better question!
Unfortunately, this test shed no light on the answers to either question.
If you put the same power adder on the 10:1 engine, would that require subtracting enough ignition advance to erase the 50hp head start?
I went with middle of the road 9.5 to 1 with my turbo coyote motor for longevity and forgiveness. I know the stock compression ratio is higher and guys boost them but they're not out there every weekend at 7500rpm either.
I like lower static compression simply due to the reduced fuel cost. That's the biggest long term expense for someone that actually drives their pile on the street, after all. 87 octane, all day every day.
If you are concerned about fuel cost, why build a 540CID engine?
@@taylorsrus9543 Because it's still a 540 cube engine. No reason why you can't run some 112 in it at the track. No reason to need 98 when you're on the street. Just add more nitrous or turn up the boost another pound or three.
I believe we have reached the next plateau in internal combustion engines. Now the parts are stronger can we get the cooling and lubrication systems to meet these higher demands???
Compression is great for power and if you have detonation issues add a camshaft with overlap to help I like compression with less boost then lower compression high boost
if you have e85 avaiable i see no reason to run at 8.5:1, a roots blown pump gas street deal, the lower compression might be good, gets hot low quality fuel hot day ect. iv been running a blower on 9.5:1 cr 8lbs of boost with e85 for years im pretty sure if i turned it up higher i would find the horsepower limit of my rotating assembly before id run into detonation.
My 540 is 14 to 1 compression with a 284 298 at 50 cam 112 degree lobe separation. Going to add twin 88 s with . what do you think?
SURE
Time and place for everything. I feel like fuel and ignition control technology has come so far that the low compression boost rule of thumb has gone out the window, especially considering fuels like e85 with such a cool burn are widely available. I have an 11:1 ls that was a max effort n/a setup that now has a 78/75 on it and I don’t have a care in the world even on 93- I put a terminator on it and I tell it what to do, if it never sees big timing at high boost and it always hits my pig rich target afr it’ll live for a while. However, I still have my first car with a tpi (well, stealth ram) and a 7730 sd ecm which I refuse to change. I have an fmu and a 6btm box- that setup isn’t controllable enough for me to be comfortable tossing a ton of compression at it. So I guess there’s no end all be all answer other than “you can get away with it if you really want to”
If you’re running two turbos individually ( non compound) I would think that 10.5:1 cr would work well with 13 lbs-14 boost with a 245@.050 .600 lift roller compression. Am I correct? I want to build a 416 ci engine with a 1000 hp at 6000 rpm peak. It is an FE. I would think that it would be a streetable E85 engine.
yes-alum heads would be a good idea
On a street or track car Low compression is not necessary nor is it beneficial with modern engines and tuning components. Now if you are using old school tech YMMV, but with newer engines and newer ECU systems we have enough control and good enough fuel available to run wild compression with boost and this is beneficial for a number of reasons.
Me with my turbo ls1 (i know different style engine/configuration) I've almost finished building it, i like my comp around 11:1 with boost and race E85 , yes gives you some safety margin and the comp will give me decent torque down low and won't be a absolute pig with no throttle response etc when not really on much boost..So yeah definitely comp for me 💪
I don’t play with old v8 stuff. But on my 4g63 I run 10:1 and any e85 only car I build the motors 10:1. Motor has seen 47psi from a 67mm turbo and 788whp. E85 is amazing stuff. Performance is on par with c16.
My ls 6.0 was told to go 9.5:1 with E85 and over 15 psi boost 1200 hp.
Now if I switch to methanol do I need to change anything compression, ring gap, bore hone, I am unable to find anything related.
Maybe a Q&A on switching fuels.
switching fuels is fine-nothing needed to change but the tune and possibly injector size and fuel pump to handle the increased fuel flow
Diesel motors are very high compression for ignition and they run boost no problem.
Like you've said many times, boost is just a measurement of inlet restriction. I'd love to know the difference between 10 to 1 comp and 8.5 to 1 comp making the same power irrelevant of boost, what is their peak cylinder pressure? Is there a difference? And if so, does the temperature change? Does this change volumetric efficiency?
I think there is a sweet spot, and the rules/ guidelines change depending on the fuel being used. And thus can drastically change the output and behaviour of an engine. I feel there is probably the point of diminishing returns also - will have to wait and see you test some more!
They are also as heavy as a big block gas engine