Is It Worth It?! Increasing Compression Ratio for MORE Horsepower
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- Опубліковано 21 вер 2020
- A common question with the Pontiac 6X and other low compression heads, is - is it worth it to spend the money increasing compression ratio numbers to increase horsepower? A common practice in the Pontiac engine building world is to pick up a set of cheap 6X-4 or 6X-8 heads and mill them down to 85-90cc head chambers, as well as zero decking the block.
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We got further with our build. So we had to go .40 over on our 72' 455, heads have been done also (7M5), so we are trying to getting the compression up by running some dome pistons, we also are running a melling RAM Air IV cam and also a set of Ram Air III manifold headers. What do you think about this combination?
Thanks for the comparison, when you start getting into higher compression builds, there are a couple more factors you have to consider; What elevation will I be running at, what is my quench factor, and Timing,Timing, timing, customize your distributor curve, and your cam choice is a big factor. I run 10.2:1 with 670 72cc heads on 91 octane, at 4500' and it's just fine.....and fast;)
The amount of arguments I've had on Facebook lately about dynamic compression ratios are killing me. I don't care what anybody says, with the right cam and timing you can run dang near any compression ratio.
@@LSxHunter I agree 100% A good percentage of people disagreeing with compression ratio being too high havent built an engine of their own, not to mention make dumb camshaft choices because they read and believe what they read.
Dynamic compression ratio explained please. 😊
9.5:1 is pretty damn standard for Iron heads. Not sure where you’re getting you info from.
You’re not going to have knock issues with a CR of 9.1. Even with 87 octane.
Hello there, for octane or ron100, what's the maximum compression ratio i may go up to, for this fuel, well not too close but on the safer side??? Thanks mate.
I have a 2013 Acura TL I was considering going with 12.4 CR, do you think that's too aggressive for the j35 engine? And do I need e85 or can I stay with 93?
Just got 12:1 for my 355 . What do you suggest
from 9:1 to 10.5:1 will it be safe for the engine?? will i need other cums?? here in greece we run with 95 octaine at least
I’m wanting to build a 455 and have a choice of 4X, 6X-8 or 6X-4 heads with stock lower end. Cam is unknown at this point but it’s a street engine, occasional track maybe. Best local gas is 94 octane with no ethanol. Thanks!
On a 455 I'd likely reach for the 6X-8s. For most people they're undesirable since they have the larger chamber but that gives you around a 9:1 compression ratio. 4X heads are a crapshoot and they tend to flow significantly less than 6X heads. 4X heads can be pressed or screwed in studs as well as 1.96 or 2.11 intake valves. The 6Xs are a known quantity and most shops are familiar with porting them down the road.
Jasper engines cat lol
I would like to see 428 and casting 48 heads with different cams including the 041. My plan is to make a weekend cruiser. Thinking about replacing my th400 with a 7004r.
Shoot me an email at rtaylor@lsxhunter.com
Sent ya a reply! Thanks for reaching out!
10:1 will run on 93 with right timing
The block I'm running is a 481988 with stock internals and the stock 4x heads, but I bought a set of #16 heads for this engine. Would I be able to use them, or would this still put my compression too high?
Early 70s 400? You'd likely need to run 91ish octane as you'd be in the 9.5-10:1 area. I'm a fan of ditching the 4X immediately. The #16s are great heads. It depends also if your engine had dished pistons or the flat tops - if they're dished I'd slap it together. It's typical for Pontiac to rate their stock engines at 0.50 point of compression more than they actually are.
@@LSxHunter Thanks for a quick response and help! I smashed that subscribe button, I'll have to check out your other videos when I get off work!
Not if it’s cammed correctly.
My question is how high compression can I go running 91 octane on a 350 chevy with iron heads and a very small duration camshaft 201/207@50 duration and 114 lobe separation? 9.5 to 1 or 10 to 1 be the cut off point? I want put all the compression I can into it with a little timing and not have pinging issues. I'm building it for a low rpm torque and mileage engine.
Look how indmar builds their old 350 vortec marine engines. 9.4:1 cr and run on 87 octane. Produce 325HP+ @ 5500 RPM with a ton of torque. These engines are built to sustain constant heavy loads.
There is no knock concern with higher compression on these engines. Once you approach 10:1 you will need to run 91+ octane.
You just have to have a performance cam to get away with it. “higher lift”.
People run into knock when they increase compression on a stock cam. OR they had their timing over advanced; then raised CR without re-timing.
@@tthams73 isn't it the dynamic compression which is controlled by the camshaft specs to determine the psi pressure? I have a 383 with 200psi cranking compression and it runs on 87 octane just fine with pinging. It's about 9.5 compression and 8.0 dynamic.
Hey I'm running LS1 only stock 241 heads but have 238 242 .603 .603 @ 112 how much could I take off my heads to have safe PVC and could I use thinner head gasket .only got 350rwhp all Bolton's headers etc 4l60e n 4 K stall take lot off it,I want to get over 400rwhp should I pp the 241s or source some 243s n pp them,will be adding 25% under drive pulley aswell anything to add compression n power would be helpful .love the big cam just needs heads get most out of it
If you haven't fondled the 241s the 243s WILL make more power. You can get the GTO 243s cheaper since they didn't come with sodium filled valves.
If it were me I'd go used 243 heads, thin gaskets, and maybe a port job. I'd assume if you ported the 241s you might end up around stock 243s but some people have great CNC setups to make the 241s work. That cam should be plenty big enough to move air, it's bigger than the SS2.
What RPM are you shifting at?
@@LSxHunter it's Australian cam range vcm 13 rev range is 4500 to 7000 need a 4k stall at lowest,only got tuned bit over week ago shift between 6500 -7 I'd be guessing going flat out,241s haven't been touched just springs etc to suit the cam,I can get 241s pp n decked 900 Aus currency or 243s new castings looking about 700 than Pp cost on top,or are there other heads good priced best bang for buck HP can get shipped over from USA?regards love your vids,ppl want heaps here in Aus for 243s
@@solangus7730 I'm a fan of use what ya got - a good CNC'd set of 241s with valve upgrades should flow 280-300cfm at .600 which puts you in a pretty good spot. If you're going to PP it's worth decking like you're saying.
When you increase the port volume you'll be losing low end torque, that can be regained by increasing compression.
Thanks for watching! For some reason we've got a bunch of people watching from Australia.
@@LSxHunter what about milled and pp 706 on a ls1?
What program are you using there on your computer?
Engine Analyzer by Performance Trends. There are different "levels" of these, with many add on programs. Also other programs / equipment for many other things. I highly recommend these programs by Performance Trends. I did just post a more elaborate comment on this subject if you want a little more information & educated opinion/advice. I would also do a search on all of this
What’s your opinion on 4x heads on a 455 with flat top pistons. Thanks
I've got a personal gripe against the 4X because of the wild rolling changes during their run. I've seen them in 1.96 and 2.11 as well as 95cc and as large as 112cc. For a 455 I'd look for 6X-8s since they for sure have large valves, better flow, and larger chambers. The 6Xs also give you the option of milling later as well if you want to make a jump to race gas.
How about the 96 heads compared to the 6x?
@@markburkey6371 the compression should be comparable to like a 6X-4 head. Everything I've seen their nearly equal with the 96 flowing a HAIR better unported. The 96 should be the same 2.11/1.77 valves with a 96cc chamber vs the 6Xs 2.11/1.66 valves and 92cc chambers.
Do not run O.O3O" quench, or your kissing the heads with your pistons on a zero deck or not a zero deck. There is no more benefit beyond O.O35" besides. And even that is a tall order even with an rpm limit of 4500 and all densely forged exotic materials, more exotic than 4340 forgings even then the pistons are kissing just softly. You want at least 175 psi cylinder pressure on anything or the engine's tune is not worth the octane. You want quench exactly at .039" to .040" no matter what deck clearance or head gasket you run, You do not adjust compression ratio with head gasket measurement. It is not merely piston design type that determines your compression, Those are very broad and vague generalizations that could be all the points off of target compression as any types of pistons. The proper way to design compression is the head chamber CC volume and the piston's CC volume = NOT head gasket or piston to deck clearance for witch you want Zero and use a O.O39" or O.O4O" head gasket for the exact same quench area. This keeps heat out of your top piston ringland that causes all the rolls canargally engine problems and burning oil cracking pistons and wear and power loss. To achieve beyond the 350-380hp barrier and be a good engine this needs done properly. Efficiencies shall always be up. For example the ZZ350 crate engine measured in with 195PSI and is why it is such a great performance engine for stockish camaros and such although it needs 93 octane. It's fast burn vortec head chamber and runner design and cooling properties allow the chevy iron to mitigate and keep away any hot spots that could lead to detonation (engine knock). always check piston to valve clearance and design the valve reliefs to match angle and give .080" piston to valve clearance intake and O.1OO" exhaust valve these are absolute minimum figures respectively. This can be done by machining or using a simple dremel tool on the piston area to be shaped to specification, also be aware of hollow domes or piston design when doing this, your target piston should be a little tighter before final cc'ing as far as CC relief although not necessarily valve to piston clearance, this way if you need to clearance the pistons slightly a few cc's lost shall bring it closer to the target. Same with head CC, get a tighter CC in the chamber than required so when you CC heads you do not need to add material, although perhaps removal of material during porting and final chamber shaping is often desired. For example i am running pistons above deck O.OO2" so instead of a O.O4O" head gasket i use a O.O41" head gasket for my O.O39" quench area.
Is that why Honda are better
What program is this
Performance Trends Engine Analyzer Pro - worth picking up for sure!
You don’t loos anything except your wallet running higher octane.
Junk. Build a 15:1
Not worth it. My mate decreased CR from 10:1 to 9:1 on his project car. Now he revs higher and makes more power. After that he even decreased it to 8:1 and increased turbo boost. All in all he is making 400 hp to the wheels from a 2.0 turbo.
How much psi for 400hp?
@@lilmixdboy i think its 17 psi if i remember correctly
@@creatineenjoyer7345 impressive if so
With turbochargers the lower the compression the more boost you can do safely higher compression you can’t use much boost so either is worth it depending on your build
Not possible