Great read- re post from Holly Lots of work done on a computer and dyno with these heads CYLINDER HEADS Of course, the first major change incorporated into these heads is the direct port injection into completely new head castings. The port of entry for the fuel is between the intake and exhaust valves directly across from the spark plug. In terms of chamber design, the idea is to minimize the volume and surface area to maximize efficiency, which the Gen V does very well. Way back in 1955, the original small-block Chevy’s valve angle was 23 degrees. This angle is referenced against a line parallel to the bore, making the valve angle 23 degrees from vertical. As knowledge of airflow progressed, these angles have progressively moved toward vertical. The ‘60s big-block Chevy introduced a canted angle to tilt the valve head away from the cylinder wall to improve flow. By the late ‘90s, the Gen III engine pushed the angle to 15 degrees and the LS7 bumped that to 12 degrees. The Gen V engine combined the advantages of a taller intake valve angle of 12.5 degrees with a splayed or tilted angle of 2.6 degrees similar to the Rat motor. The exhaust valve also moved to 12 degrees with a 2.4-degree tilt. All of this is aimed at improving airflow from what were already large rectangular intake ports. (Left) This chamber photo reveals not only the large-by-huge 2.130/ 1.590-incih valve sizes but also the mechanical injector location just opposite the spark plug. Factory engines run an iridium-tipped spark plug. (Right) Among the somewhat esoteric changes made to the Gen V lineup is a switch in the valve layout. The upper head is the Gen IV rectangle port head contrasted with the Gen V LT1 below. Note how the intake/exhaust valve orientation has switched. This change also alters the intake and exhaust lobe layout on the camshaft. On top of everything else, GM engineers also re-oriented the valve layout. Gen III/IV engines organized the LS into a symmetrical port configuration similar to the traditional small-block Ford. This eliminated the siamesed pairing of the small-block’s center exhaust ports. The Gen V places the exhaust port on the leading edge of the front cylinder whereas the Gen III/IV placed the intake port at the front. This re-orientation was performed to allow a more direct path between the intake manifold and the cylinder. Of course, the Gen V camshaft lobe layout also had to change to mimic the heads. Another change that is more obvious is the extremely large intake port configuration that is closer to a square with a wider base compared to the Gen IV’s vertical rectangle orientation. Comparing volume numbers can often be deceiving, so be wary of direct comparisons between the LT1’s intake runner at 297cc with the previous rec port LS3 at 257cc. The LT1’s intake valve is actually slightly smaller than the Gen IV LS3 heads with the Gen V at 2.13 / 1.59-inches while the earlier LS3 sported the same size exhaust but a larger 2.165-inch intake. The 5.3L engines with smaller bores breathe through smaller valves. Advancements in chamber design now spec increasingly tighter chambers so the LT1/LT2 measure barely 59cc’s while the supercharged LT5 is slightly larger at 65cc’s to compensate for the added boost pressure. The exhaust ports are still space symmetrically and exit in roughly the same relationship to the Gen III/IV heads, but the Gen V bolt holes are in a completely different location. This means that headers or manifolds for a Gen IV will not bolt up to the LT or any of its immediate family members. We can expect that Gen V headers should be fairly quick in forthcoming since manufacturers will only need to re-orient their exhaust flanges and drill new bolt holes.
Thank you Richard, when I first got to LS land I had people call me crazy for Frankenstein head combos when I got here lol. 799s are now the go to cheap compression fix for 4.8/5.3 turbo builds I see around on social media lol... Its crazy what happens in five years lol
Why would you need to do a compression fix on the 5.3L-the compression is already good for a turbo. The go-to heads for a 5.3l are the heads that came on it
Im curious about lsa vs ls3 etc in the same way we talk about the cath port heads. Because the blower Im using, the lower makes more sense going into a rec port. Which allows me to make my CR adjustment there, by swapping heads as the package change when the blower comes, versus the 12:1 NA 408 thatll be down there existing. Very long sighted on my part, but I like to know what my next ten moves will be so I can snag something out of order if the cost is right lol.
Richard - I think the issue is using the word “ flow” The engine is a simple air pump. If you took a small bore syringe Or a large bore syringe They both draw in the same flow( the needle) So what is the difference? Velocity!!( less bore less draw- less air speed The smaller bore - yes it will work But as a rule at the same rpm A smaller flow head makes more power on a bigger bore Than a big flow head on a smaller motor Now if you put in a extreme cam Think boss 302 Chevy 302 They are a bit of a dog in low rpm Because of high “ flow” heads But spin them up 6000-8000 rpm The small flow heads restrict “ flow” Now small “ flow “ heads on a big bore the air “ flow” travels much faster to the camber Making a far far snappier response!!! Now if it’s a big cam( long duration ) As it gets up the rev range it will “ starve” for volume High lift is better for small head big bore( less duration) Small lift long duration for big head small bore This said all chamber size the same Remember big head on small bore - it’s lost to swish or quench anyway on zero deck LS As a rule you should know the rev range Auto or stick High velocity is always better Than low velocity due to chamber swirl/ fuel mix It’s a fine balance You and I both know Heads don’t control TQ Intake controls TQ This is my personal belief Do you agree? -don
@ maybe high swirl combustion chamber? Great quench? Honda has spent years of research on burn think ccvc or my CX 500 turbo V twin push rods 4 valves FI A 4 stroke v twin just about the worse thing to turbo as the pulse is so spead out the added surge tanks Reed valves in at the time the world’s smallest turbo spinning 2.5 time that of a reg one AT 250000 rpm Low turbo lag no intercooler 19.5 lbs boost It may also be pluse tuned Honda is maybe the best for a complete burn I will have a look I don’t know that engine- Don
@ ok so a “B 16” Is really two engines One high velocity , one high flow How you ask? V tec at the best speed a pin moves sideways and adds another cam profile maybe even another valve It’s something like fiat “ multi air” That’s three engines in one The B-series are a family of inline four-cylinder DOHC automotive engines introduced by Honda in 1988. Sold concurrently with the D-series which were primarily SOHC engines designed for more economical applications, the B-series were a performance option featuring dual overhead cams along with the first application of Honda's VTEC system (available in some models), high-pressure die cast aluminum block, cast-in quadruple-Siamese iron liners.[1]
@ They were made in 1.6 L (1,595 cc), 1.7 L (1,678 cc), 1.8 L (1,797 cc), 1.8 L (1,834 cc), and 2.0 litres (1,973 cc) variants, with and without VTEC (Variable valve Timing and Electronic lift Control). Later models have minor upgrades including modifications to the intake valves and ports and piston tops, along with individual cylinder oil injectors (B18C models). They produce between 126 hp (94 kW; 128 PS) and 190 hp (142 kW; 193 PS), with some models capable of a redline over 8500 RPM.[4] Lift/ valves/can all changing Great 6000 rpm motor And 8500 rpm motor( that’s why the huge ports) All In one
@ yes it’s two engines in one high velocity, one high flow All in one with active valve and cam profile The VTEC system provides the engine with valve timing optimized for both low- and high-RPM operations. In basic form, the single cam lobe and follower/rocker arm of a conventional engine is replaced with a locking multi-part rocker arm and two cam profiles: one optimized for low-RPM stability and fuel efficiency, and the other designed to maximize high-RPM power output. The switching operation between the two cam lobes is controlled by the ECU, which takes account of engine oil pressure, engine temperature, vehicle speed, engine speed, and throttle position. Using these inputs, the ECU is programmed to switch from the low-lift to the high-lift cam lobes when certain conditions are met. At the switch point, a solenoid is actuated that allows oil pressure from a spool valve to operate a locking pin, which binds the high-RPM rocker arm to the low-RPM ones. From this point on, the valves open and close according to the high-lift profile, which opens the valve further and for a longer time. The switch-over point is variable, between a minimum and maximum point, and is determined by engine load. The switch-down back from high- to low-RPM cams is set to occur at a lower engine speed than the switch-up (representing a hysteretic cycle) to avoid a situation in which the engine is asked to operate continuously at or around the switch-over point. The older approach to timing adjustments is to produce a camshaft with a valve timing profile that is better suited to low-RPM operation. The improvements in low-RPM performance, which is where most street-driven automobiles operate a majority of the time, occur in trade for a power and efficiency loss at higher-RPM ranges. Correspondingly, VTEC attempts to combine low-RPM fuel efficiency and stability with high-RPM performance.
It’s so much deeper than “more flow” and Richard knows that ….not sure what he’s comparing ….the “area under curve “ is more telling than the peak # too…..🤔
Im curious if the center weight modification on an l8t crank can be done to fit in a gen3 small bore by a diy in their garage the way a snout can be milwalkeed of an ls7 crank to shove in an lq4/9... Im not entirely sure whats being described there. Is it a simple clearancing issue or are we talking have things reballanced kind of heavy metal removal?
You trigger thoughts of trying to consistently load drive wheels off the ground for tuning lol... Ive mucked around with tuning on jackstands, if only there were like harbor-freight wheel rollers we could provide load with lololol. Like, we dont actually need a dyno we just need loaded rollers for tuning lol...
@Richard Holdener I missed the live show and have a good question. Let's take a 383 sbc for instance. Does combustion chamber size effect intake port flow? Say, 65cc vs 55cc with 210 cc intake port. Flow 311@ .600 lift
@richardholdener1727 Well, I guess we'll see. Good news is, I found a dyno tuner. I will give you the numbers when I get this porject going on the road.
Right sized head- NA or Boosted it seems every one is looking for the Big Number Max power They chased this on snowmobiles years ago But they may have reached the peak speed( not unlike a dyno ) Seat of the pants and real world spoke otherwise Richard I think moving forward you may want to include avg HP /TQ Even then to date nothing ( other that driving) Tells you time to power On two strokes we call it a “ fat curve” Meaning the sled pulls strong when you hit it a short Time to power Take any old motor 400 hp Verse New motor 400 hp It feels and is faster/ bigger? Due to reduced friction and drag in design Old super car from the late 60s early 70s 320 hp Is blown away by a modern truck engine It’s apples to oranges Avg power with peak power Is a better gauge for Heads Cams Intakes Everything And as always cost per smilles We all freak when we get a deal It’s the best part of every story Thanks - Don I have head this many times “ rec port heads make more power…..” Do they? If you chop up a dyno sheet into 100 rpm At the same range say 3000-6000 Add and divide That’s the true power
Re post- A useful tool for calculating the power potential of cylinder heads is the following formula HP=. 257 x (peak) airflow x number of cylinders. If we plug in flow data from a CNC-ported small-block cylinder head that offered a peak flow of 304 cfm, we get the following: HP=. 257 x 304 x 8 or 625 hp.
I was of the understanding that the unshrouded of aftermarket over bore like 4.50 on BBC does see noticeable bump in power vs a notched factory bore. Too me it sounds like you saying more head flow better shrouding or no shrouding.
Nothing wrong with notching the bore just like a performance built Rats came with . Even the sbc usually needs notched to maximize flow . Most never do this on them . Myself i like the coefficent of discharge a slightly smaller valve offers in effiecency . A smaller shallower chamber is supierior combustion as well which isnt considered enough . A bigger port will just come on later when its velocity increases to no longer pulse . A 862 on a 4.8 is 4000 , 862 on a 5.3 is 3500 for example . Too much gained know how is being overlooked today from days gone by . Thats a waste !!!
Bingo, big exhaust valves don't make sense till you're moving a ton of air. It's a volume/velocity thing people miss. They wanna think about air like their fat wife in a doorway 🤣 Velocity is so important lol. Don't let me boggle any two valve minds with concepts like swirl port design or variable length intake runners 🤣
Hint: this is why I'm obsessed with the LT5 from the ZR1 lol. It's why all the new Corvette engines are twincams with Lt designations. To benefit from 180° crank you need a valve train that's stable over 8k for one, and having two intake valves lets you take advantage of intake valve phasing for combustion swirl... Especially neat with VVT-I stuff
Certainly it can work but it won't be that good in half throttle. Possibly in the Dyno it won't be obvious, however in real driving conditions it should be. Also fuel consumption would be affected for the same reasons.
What is the difference between airflow and velocity? Flow is a measure of air output in terms of volume per unit of time. The common units are litres per minute, cubic feet per minute (CFM), etc. Velocity refers to how fast the air is moving in distance per unit of time. The common units are feet per second, metres per second, etc. A flow bench only measures one part The formula changes With every intake And every engine( bore/ stroke) Just like you see this people put their muffler on a flow bench and tell you look it flows better We are not running benches The pulse wave changes at speed Any one that drove and two stroke that “ comes on pipe” Knows this there is a huge surge in power Every air pump can have a tuneable sweet spot
I'm building my first motor my dad died and I'm rebuilding his 99 Silverado 5.3 bored to 5.800 forged icon pistons gen 4 rods tbss intake manifold and 243 heads and I'm going to be going turbo with it I got a 4l80e I'm going to attempt to rebuild myself I was worried about the 862 head's having to much compression my turner says I should have 650 to 700 horse power what size turbo do you recommend for it
A flow bench is not a true Reading - you have a constant flow( from a constant draw of the air pump) Engines are “ pulse charged” Due to the intake valve opening and closing The frequency of the pulse is tuneable called resonance Watch and carb on a dyno Or any old two stroke open carb you can see the “ charge” pulsing in and out If you could cut a LS into 8 separate cyl every thing the same you would make less power( 1x8) Than all 8 together On the intake side at closing the return sonic wave feeds the other open cyl On the exhaust side The manifold or header Scavenges the spent exhaust Both clearing the chamber If spent gas ,and making draw for new charge If you follow constant flow combustion Like a jet Verse a pulse jet Great re post to help explain What your up against A “j” pipe on a muffler tunes some what the same ricky said: 09-04-2006 04:09 PM Default N/A intake resonance tuning I started planning my 18RG--> quad throttle body conversion this afternoon. I just wanna get this information on the site so that others can look over it, add anything I've missed and confirm/refute my theory. Basic stats are as follows: Engine:18RG Bore x stroke: 89.5 x 80mm Cam adv duration: 288* Goals of conversion: 18R-GE running 4A-GE S/T quads (43mm), resonance tuned. Run by megasquirt. Now, firstly, a resonance intake system will optimally have a peak mean intake charge velocity of 300ft/s = 91.44m/s. This velocity is dictated by the greatest restriction in the runner, and can be calculated as follows (assuming 100% VE): Peak mean velocity = (Mean piston velocity x piston area)/runner cross sectional area ...(1) And mean piston velocity is dependent upon stroke and rpm. I aim for a redline of around 8000rpm, so: Mean piston velocity = stroke x frequency x 2 ...(2) = 21.33m/s Since runner X-sectional area is (re-arrangement of (1)): (Mean piston velocity x piston area)/Peak mean velocity, we get A = 1452mm^2, So d = 43.2mm, so S/T throttles are a good match. Now, since the 18RG is an 8V engine, VE is likely to be crap, so in reality, this velocity would probably occur higher in the rev range. Now comes the tricky part... Tuning the runner length. We want the wave reflected by the closing intake valve to reflect and hit the intake valve just as it begins to open again. My cams have adv duration of 288*, so they are closed 432*/720*. This equates to 1.2 crank revolutions. Say I tune this for 7500 rpm, the period = 0.008seconds/rev, so our window for reflections is 0.0096seconds. The path length of the reflected wave is: length = Avg velocity x time ...(3) What is the average velocity? Literature states that the reflected wave travels at the speed of sound, but where does the extra energy come from? I'd like to think that the pressure waves travel at the instantaneous velocity of the intake charge as the valve closes. In my case, this is the instantaneous velocity at 75*ABDC, which I don't care to calculate at the moment. For speed of sound, l = 340 x 0.0096 = 3.264m, so first harmonic is runner length = l/2 = 1.632m since the wave must travel up then down. Obviously, the first harmonic is inaccessible due to space constraints... For a lower velocity, say 75% of mean peak ~70m/s, l = 67cm so l/2 = 33.6cm. In this case, the 2nd harmonic is perfectly useable, with a runner tip to valve length of ~17cm. Of course, this is all still partially black art, and to properly implement this, I anticipate dyno time and a telescoping toilet roll trumpet to tune the solution around systemic uncertainties. Can anyone shed any light as to why literature states the wave velocity to be the speed of sound? This just seems wrong!
Stock ECUs I've been messing with have timing reduction at colder and hotter temps, so yeah, I'd assume there's knock risk with a bigger intercooler. Colder air is already more dense, so it compresses to a higher pressure over the same compression ratio. I like this grams per cylinder timing stuff; just makes sense. Why I'm annoyed with custom firmware that just does a boost retard. Like damn, you figured out enough to do closed loop with a wideband, but then caveman that implementation? Figure out how to extend the grams per cylinder range; that can be done by putting in the "wrong" calibration data by the way. 2 BAR MAP on a 1 BAR calibration, injector flow calibration set to half what they really do. Low effort doubling of grams per cylinder limit. Of course, you have to keep that in mind while logging. And I put zero thought into the MAF since I don't respect that sensor anyway.
I think that after market heads may make more “ peak “ power if that’s what your goal in still their is drivability You take a look at new LT heads There are some great tricks in there Reduced angle Canted valves Unshroulded valves Toss a port intake on Chuck the lean burn pistons Your taking power 351 Cleveland tribute head
Good evening sir I have my new short block done looking for a good cylinder head for it the bore is 4.630 6.7 rod with a 4.75 stroke planning a super charged induction any help would be appreciated thanks again
Great read- re post from Holly
Lots of work done on a computer and dyno with these heads
CYLINDER HEADS
Of course, the first major change incorporated into these heads is the direct port injection into completely new head castings. The port of entry for the fuel is between the intake and exhaust valves directly across from the spark plug. In terms of chamber design, the idea is to minimize the volume and surface area to maximize efficiency, which the Gen V does very well.
Way back in 1955, the original small-block Chevy’s valve angle was 23 degrees. This angle is referenced against a line parallel to the bore, making the valve angle 23 degrees from vertical. As knowledge of airflow progressed, these angles have progressively moved toward vertical. The ‘60s big-block Chevy introduced a canted angle to tilt the valve head away from the cylinder wall to improve flow. By the late ‘90s, the Gen III engine pushed the angle to 15 degrees and the LS7 bumped that to 12 degrees.
The Gen V engine combined the advantages of a taller intake valve angle of 12.5 degrees with a splayed or tilted angle of 2.6 degrees similar to the Rat motor. The exhaust valve also moved to 12 degrees with a 2.4-degree tilt. All of this is aimed at improving airflow from what were already large rectangular intake ports.
(Left) This chamber photo reveals not only the large-by-huge 2.130/ 1.590-incih valve sizes but also the mechanical injector location just opposite the spark plug. Factory engines run an iridium-tipped spark plug. (Right) Among the somewhat esoteric changes made to the Gen V lineup is a switch in the valve layout. The upper head is the Gen IV rectangle port head contrasted with the Gen V LT1 below. Note how the intake/exhaust valve orientation has switched. This change also alters the intake and exhaust lobe layout on the camshaft.
On top of everything else, GM engineers also re-oriented the valve layout. Gen III/IV engines organized the LS into a symmetrical port configuration similar to the traditional small-block Ford. This eliminated the siamesed pairing of the small-block’s center exhaust ports. The Gen V places the exhaust port on the leading edge of the front cylinder whereas the Gen III/IV placed the intake port at the front. This re-orientation was performed to allow a more direct path between the intake manifold and the cylinder. Of course, the Gen V camshaft lobe layout also had to change to mimic the heads.
Another change that is more obvious is the extremely large intake port configuration that is closer to a square with a wider base compared to the Gen IV’s vertical rectangle orientation. Comparing volume numbers can often be deceiving, so be wary of direct comparisons between the LT1’s intake runner at 297cc with the previous rec port LS3 at 257cc. The LT1’s intake valve is actually slightly smaller than the Gen IV LS3 heads with the Gen V at 2.13 / 1.59-inches while the earlier LS3 sported the same size exhaust but a larger 2.165-inch intake. The 5.3L engines with smaller bores breathe through smaller valves. Advancements in chamber design now spec increasingly tighter chambers so the LT1/LT2 measure barely 59cc’s while the supercharged LT5 is slightly larger at 65cc’s to compensate for the added boost pressure.
The exhaust ports are still space symmetrically and exit in roughly the same relationship to the Gen III/IV heads, but the Gen V bolt holes are in a completely different location. This means that headers or manifolds for a Gen IV will not bolt up to the LT or any of its immediate family members. We can expect that Gen V headers should be fairly quick in forthcoming since manufacturers will only need to re-orient their exhaust flanges and drill new bolt holes.
Thank you Richard, when I first got to LS land I had people call me crazy for Frankenstein head combos when I got here lol.
799s are now the go to cheap compression fix for 4.8/5.3 turbo builds I see around on social media lol...
Its crazy what happens in five years lol
Why would you need to do a compression fix on the 5.3L-the compression is already good for a turbo. The go-to heads for a 5.3l are the heads that came on it
Richard holdener you have alot of amazing information on technical vehicle information thank you for sharing & do you have books on this information?
I wrote 10 different books on different engine families
Thanks for your hours of I fo..!!
Im curious about lsa vs ls3 etc in the same way we talk about the cath port heads. Because the blower Im using, the lower makes more sense going into a rec port.
Which allows me to make my CR adjustment there, by swapping heads as the package change when the blower comes, versus the 12:1 NA 408 thatll be down there existing.
Very long sighted on my part, but I like to know what my next ten moves will be so I can snag something out of order if the cost is right lol.
Richard - I think the issue is using the word “ flow”
The engine is a simple air pump.
If you took a small bore syringe
Or a large bore syringe
They both draw in the same flow( the needle)
So what is the difference? Velocity!!( less bore less draw- less air speed
The smaller bore - yes it will work
But as a rule at the same rpm
A smaller flow head makes more power on a bigger bore
Than a big flow head on a smaller motor
Now if you put in a extreme cam
Think boss 302
Chevy 302
They are a bit of a dog in low rpm
Because of high “ flow” heads
But spin them up
6000-8000 rpm
The small flow heads restrict “ flow”
Now small “ flow “ heads on a big bore the air “ flow” travels much faster to the camber
Making a far far snappier response!!!
Now if it’s a big cam( long duration )
As it gets up the rev range it will “ starve” for volume
High lift is better for small head big bore( less duration)
Small lift long duration for big head small bore
This said all chamber size the same
Remember big head on small bore - it’s lost to swish or quench anyway on zero deck LS
As a rule you should know the rev range
Auto or stick
High velocity is always better
Than low velocity due to chamber swirl/ fuel mix
It’s a fine balance
You and I both know
Heads don’t control TQ
Intake controls TQ
This is my personal belief
Do you agree?
-don
A B16 Honda has a port bigger than any Boss motor. Why isn’t it a “dog” down low?
@ maybe high swirl combustion chamber? Great quench?
Honda has spent years of research on burn think ccvc or my CX 500 turbo
V twin push rods 4 valves FI
A 4 stroke v twin just about the worse thing to turbo as the pulse is so spead out the added surge tanks
Reed valves in at the time the world’s smallest turbo spinning 2.5 time that of a reg one AT 250000 rpm
Low turbo lag no intercooler 19.5 lbs boost
It may also be pluse tuned
Honda is maybe the best for a complete burn
I will have a look I don’t know that engine- Don
@ ok so a “B 16”
Is really two engines
One high velocity , one high flow
How you ask?
V tec at the best speed a pin moves sideways and adds another cam profile maybe even another valve
It’s something like fiat “ multi air”
That’s three engines in one
The B-series are a family of inline four-cylinder DOHC automotive engines introduced by Honda in 1988. Sold concurrently with the D-series which were primarily SOHC engines designed for more economical applications, the B-series were a performance option featuring dual overhead cams along with the first application of Honda's VTEC system (available in some models), high-pressure die cast aluminum block, cast-in quadruple-Siamese iron liners.[1]
@ They were made in 1.6 L (1,595 cc), 1.7 L (1,678 cc), 1.8 L (1,797 cc), 1.8 L (1,834 cc), and 2.0 litres (1,973 cc) variants, with and without VTEC (Variable valve Timing and Electronic lift Control). Later models have minor upgrades including modifications to the intake valves and ports and piston tops, along with individual cylinder oil injectors (B18C models). They produce between 126 hp (94 kW; 128 PS) and 190 hp (142 kW; 193 PS), with some models capable of a redline over 8500 RPM.[4]
Lift/ valves/can all changing
Great 6000 rpm motor
And 8500 rpm motor( that’s why the huge ports)
All In one
@ yes it’s two engines in one high velocity, one high flow
All in one with active valve and cam profile
The VTEC system provides the engine with valve timing optimized for both low- and high-RPM operations. In basic form, the single cam lobe and follower/rocker arm of a conventional engine is replaced with a locking multi-part rocker arm and two cam profiles: one optimized for low-RPM stability and fuel efficiency, and the other designed to maximize high-RPM power output. The switching operation between the two cam lobes is controlled by the ECU, which takes account of engine oil pressure, engine temperature, vehicle speed, engine speed, and throttle position. Using these inputs, the ECU is programmed to switch from the low-lift to the high-lift cam lobes when certain conditions are met. At the switch point, a solenoid is actuated that allows oil pressure from a spool valve to operate a locking pin, which binds the high-RPM rocker arm to the low-RPM ones. From this point on, the valves open and close according to the high-lift profile, which opens the valve further and for a longer time. The switch-over point is variable, between a minimum and maximum point, and is determined by engine load. The switch-down back from high- to low-RPM cams is set to occur at a lower engine speed than the switch-up (representing a hysteretic cycle) to avoid a situation in which the engine is asked to operate continuously at or around the switch-over point.
The older approach to timing adjustments is to produce a camshaft with a valve timing profile that is better suited to low-RPM operation. The improvements in low-RPM performance, which is where most street-driven automobiles operate a majority of the time, occur in trade for a power and efficiency loss at higher-RPM ranges. Correspondingly, VTEC attempts to combine low-RPM fuel efficiency and stability with high-RPM performance.
It’s so much deeper than “more flow” and Richard knows that ….not sure what he’s comparing ….the “area under curve “ is more telling than the peak # too…..🤔
Im curious if the center weight modification on an l8t crank can be done to fit in a gen3 small bore by a diy in their garage the way a snout can be milwalkeed of an ls7 crank to shove in an lq4/9...
Im not entirely sure whats being described there. Is it a simple clearancing issue or are we talking have things reballanced kind of heavy metal removal?
Milwaukee'd off 😉
You trigger thoughts of trying to consistently load drive wheels off the ground for tuning lol...
Ive mucked around with tuning on jackstands, if only there were like harbor-freight wheel rollers we could provide load with lololol.
Like, we dont actually need a dyno we just need loaded rollers for tuning lol...
all that can be done on the street-we could not drive it or load it on the salt at Bonneville to tune
@Richard Holdener
I missed the live show and have a good question.
Let's take a 383 sbc for instance. Does combustion chamber size effect intake port flow?
Say, 65cc vs 55cc with 210 cc intake port. Flow 311@ .600 lift
A different chamber (including size) cam alter the flow at different lift ranges
@richardholdener1727
Well, I guess we'll see. Good news is, I found a dyno tuner. I will give you the numbers when I get this porject going on the road.
Right sized head- NA or Boosted it seems every one is looking for the Big Number
Max power
They chased this on snowmobiles years ago
But they may have reached the peak speed( not unlike a dyno )
Seat of the pants and real world spoke otherwise
Richard I think moving forward you may want to include avg HP /TQ
Even then to date nothing ( other that driving)
Tells you time to power
On two strokes we call it a “ fat curve”
Meaning the sled pulls strong when you hit it a short Time to power
Take any old motor
400 hp
Verse
New motor
400 hp
It feels and is faster/ bigger?
Due to reduced friction and drag in design
Old super car from the late 60s early 70s
320 hp
Is blown away by a modern truck engine
It’s apples to oranges
Avg power with peak power
Is a better gauge for
Heads
Cams
Intakes
Everything
And as always cost per smilles
We all freak when we get a deal
It’s the best part of every story
Thanks - Don
I have head this many times
“ rec port heads make more power…..”
Do they?
If you chop up a dyno sheet into 100 rpm
At the same range say 3000-6000
Add and divide
That’s the true power
862, ported, milled, with a 2" valve is the perfect budget head for any na gen3 and most na gen4 imho lol
Compression goes a long way lol
Re post-
A useful tool for calculating the power potential of cylinder heads is the following formula HP=. 257 x (peak) airflow x number of cylinders. If we plug in flow data from a CNC-ported small-block cylinder head that offered a peak flow of 304 cfm, we get the following: HP=. 257 x 304 x 8 or 625 hp.
simply double the peak flow
Just shows how good the LS engine is, other than head flow. Many old norms don't apply to the LS
O yeah and truck Norris cam
I was of the understanding that the unshrouded of aftermarket over bore like 4.50 on BBC does see noticeable bump in power vs a notched factory bore.
Too me it sounds like you saying more head flow better shrouding or no shrouding.
heads flow more on bigger bores-but do you already have enough flow without it
Nothing wrong with notching the bore just like a performance built Rats came with . Even the sbc usually needs notched to maximize flow . Most never do this on them . Myself i like the coefficent of discharge a slightly smaller valve offers in effiecency . A smaller shallower chamber is supierior combustion as well which isnt considered enough . A bigger port will just come on later when its velocity increases to no longer pulse . A 862 on a 4.8 is 4000 , 862 on a 5.3 is 3500 for example . Too much gained know how is being overlooked today from days gone by . Thats a waste !!!
Bingo, big exhaust valves don't make sense till you're moving a ton of air.
It's a volume/velocity thing people miss. They wanna think about air like their fat wife in a doorway 🤣
Velocity is so important lol.
Don't let me boggle any two valve minds with concepts like swirl port design or variable length intake runners 🤣
Hint: this is why I'm obsessed with the LT5 from the ZR1 lol. It's why all the new Corvette engines are twincams with Lt designations.
To benefit from 180° crank you need a valve train that's stable over 8k for one, and having two intake valves lets you take advantage of intake valve phasing for combustion swirl... Especially neat with VVT-I stuff
And I was going with I think it's a 98 turbo I haven't ordered turbo yet
Certainly it can work but it won't be that good in half throttle. Possibly in the Dyno it won't be obvious, however in real driving conditions it should be. Also fuel consumption would be affected for the same reasons.
What is the difference between airflow and velocity?
Flow is a measure of air output in terms of volume per unit of time. The common units are litres per minute, cubic feet per minute (CFM), etc. Velocity refers to how fast the air is moving in distance per unit of time. The common units are feet per second, metres per second, etc.
A flow bench only measures one part
The formula changes
With every intake
And every engine( bore/ stroke)
Just like you see this people put their muffler on a flow bench and tell you look it flows better
We are not running benches
The pulse wave changes at speed
Any one that drove and two stroke that “ comes on pipe”
Knows this there is a huge surge in power
Every air pump can have a tuneable sweet spot
I'm building my first motor my dad died and I'm rebuilding his 99 Silverado 5.3 bored to 5.800 forged icon pistons gen 4 rods tbss intake manifold and 243 heads and I'm going to be going turbo with it I got a 4l80e I'm going to attempt to rebuild myself I was worried about the 862 head's having to much compression my turner says I should have 650 to 700 horse power what size turbo do you recommend for it
you should get a 7875 turbo from VS Racing
A flow bench is not a true
Reading - you have a constant flow( from a constant draw of the air pump)
Engines are “ pulse charged”
Due to the intake valve opening and closing
The frequency of the pulse is tuneable called resonance
Watch and carb on a dyno
Or any old two stroke open carb you can see the “ charge” pulsing in and out
If you could cut a LS into 8 separate cyl every thing the same you would make less power( 1x8)
Than all 8 together
On the intake side at closing the return sonic wave feeds the other open cyl
On the exhaust side
The manifold or header
Scavenges the spent exhaust
Both clearing the chamber
If spent gas ,and making draw for new charge
If you follow constant flow combustion
Like a jet
Verse a pulse jet
Great re post to help explain
What your up against
A “j” pipe on a muffler tunes some what the same
ricky said:
09-04-2006 04:09 PM
Default N/A intake resonance tuning
I started planning my 18RG--> quad throttle body conversion this afternoon. I just wanna get this information on the site so that others can look over it, add anything I've missed and confirm/refute my theory.
Basic stats are as follows:
Engine:18RG
Bore x stroke: 89.5 x 80mm
Cam adv duration: 288*
Goals of conversion: 18R-GE running 4A-GE S/T quads (43mm), resonance tuned. Run by megasquirt.
Now, firstly, a resonance intake system will optimally have a peak mean intake charge velocity of 300ft/s = 91.44m/s. This velocity is dictated by the greatest restriction in the runner, and can be calculated as follows (assuming 100% VE):
Peak mean velocity = (Mean piston velocity x piston area)/runner cross sectional area ...(1)
And mean piston velocity is dependent upon stroke and rpm. I aim for a redline of around 8000rpm, so:
Mean piston velocity = stroke x frequency x 2 ...(2)
= 21.33m/s
Since runner X-sectional area is (re-arrangement of (1)):
(Mean piston velocity x piston area)/Peak mean velocity, we get A = 1452mm^2,
So d = 43.2mm, so S/T throttles are a good match.
Now, since the 18RG is an 8V engine, VE is likely to be crap, so in reality, this velocity would probably occur higher in the rev range.
Now comes the tricky part... Tuning the runner length. We want the wave reflected by the closing intake valve to reflect and hit the intake valve just as it begins to open again.
My cams have adv duration of 288*, so they are closed 432*/720*. This equates to 1.2 crank revolutions. Say I tune this for 7500 rpm, the period = 0.008seconds/rev, so our window for reflections is 0.0096seconds.
The path length of the reflected wave is:
length = Avg velocity x time ...(3)
What is the average velocity? Literature states that the reflected wave travels at the speed of sound, but where does the extra energy come from? I'd like to think that the pressure waves travel at the instantaneous velocity of the intake charge as the valve closes. In my case, this is the instantaneous velocity at 75*ABDC, which I don't care to calculate at the moment.
For speed of sound, l = 340 x 0.0096 = 3.264m, so first harmonic is runner length = l/2 = 1.632m since the wave must travel up then down. Obviously, the first harmonic is inaccessible due to space constraints...
For a lower velocity, say 75% of mean peak ~70m/s, l = 67cm so l/2 = 33.6cm. In this case, the 2nd harmonic is perfectly useable, with a runner tip to valve length of ~17cm.
Of course, this is all still partially black art, and to properly implement this, I anticipate dyno time and a telescoping toilet roll trumpet to tune the solution around systemic uncertainties.
Can anyone shed any light as to why literature states the wave velocity to be the speed of sound? This just seems wrong!
You need to put the meth pipe down
Is this the cattledog garage guy under a different name
@ as in the UA-cam channel guy or a fan?
As is the 823 head on the 6 liter.
Stock 243 head sitting on .052 thick 4.080 bore head gasket on lq4 .030 over piston, ok?
3.622 stroke .550 lift cam
4.080 bore?
And I was going with I think it's a 98 turbo I haven't ordered turbo yet 21:32
O yeah and truck Norris cam
19:11
Stock ECUs I've been messing with have timing reduction at colder and hotter temps, so yeah, I'd assume there's knock risk with a bigger intercooler. Colder air is already more dense, so it compresses to a higher pressure over the same compression ratio. I like this grams per cylinder timing stuff; just makes sense. Why I'm annoyed with custom firmware that just does a boost retard. Like damn, you figured out enough to do closed loop with a wideband, but then caveman that implementation? Figure out how to extend the grams per cylinder range; that can be done by putting in the "wrong" calibration data by the way. 2 BAR MAP on a 1 BAR calibration, injector flow calibration set to half what they really do. Low effort doubling of grams per cylinder limit. Of course, you have to keep that in mind while logging. And I put zero thought into the MAF since I don't respect that sensor anyway.
Are you sick !!
I think that after market heads may make more “ peak “ power if that’s what your goal in still their is drivability
You take a look at new LT heads
There are some great tricks in there
Reduced angle
Canted valves
Unshroulded valves
Toss a port intake on
Chuck the lean burn pistons
Your taking power
351 Cleveland tribute head
Good evening sir I have my new short block done looking for a good cylinder head for it the bore is 4.630 6.7 rod with a 4.75 stroke planning a super charged induction any help would be appreciated thanks again
4.630?