Advanced Engineering Tech - Stroke Only = HP?

Say on an LS1 that the only change is to a 4.0" crank. Will that alone produce more horsepower? Or will it just change the shape of the curve??

Assuming all else stays the same, only thing you will get for sure is TQ and a shift downwards in the power curve.

That is what I have always seen.

I asked because I posted in an internal thread that since stroke alone did not increase cylinder fill net hp would be approximately the same. But had several guys post contrary results including one guy reporting 42/38 stroke alone on a LS1 4.0" stroke.

A shift downward in power curve, do you mean less power or the power is moved lower in the RPM range?

He means lower RPM. You will have the ability (depending on your cam selection) to make the same power as a smaller stroke engine at a lower RPM. Eric L

^^ yep. Super Chevy did a test (on an SBC albeit, but same concept). They had a normal 355 H/C package, dynoed that. Then took the same parts and put those on a 383 bottom end with the same compression ratio. I believe torque output passed the 355 at around 3K and the power curve did too not long after that

Barring some obsurd internet designed intake or exhaust constraints, ANY increase in displacement whether by stroke or bore or both WILL increase torque AND horsepower.

It is very simple, displacement = torque = HP. Also, forget the whole long stroke means more torque, its not the stoke but the added displacement that generates the added torque. All you have to do is look at large displacement BBC based engines they get most of their cubic inches from very long strokes. Some of these engines are very high RPM setups...

Shane

What if the heads, cam, intake, exhaust were matched specifically for to maximize power in a 346ci LS1. Would adding the longer stroke still increase power, or could other setup (all things staying equal) be enough of a mismatch to the stroke that it offsets the power gained from more displacement?

Look at it this way even if the top end is the same, every intake stroke air will be pulled in and if the suction doing so is greater due to a longer stroke it should fill the cylinder more.

Yes, you will still make more power.

Shane

Also, forget the whole long stroke means more torque, its not the stoke but the added displacement that generates the added torque. All you have to do is look at large displacement BBC based engines they get most of their cubic inches from very long strokes. Some of these engines are very high RPM setups...

Shane

are you sure about this?! this really blows the whole pontiac 455's theory out of the water.

IMHO, its not as much about just the bore and stroke. Its the whole combonation that makes certian motors (I.E. Pontiac, etc) what they are. Head runner volumn, camshaft, compression, combustion chamber design, etc. Eric L

Barring some obsurd internet designed intake or exhaust constraints, ANY increase in displacement whether by stroke or bore or both WILL increase torque AND horsepower.

It is very simple, displacement = torque = HP. Also, forget the whole long stroke means more torque, its not the stoke but the added displacement that generates the added torque. All you have to do is look at large displacement BBC based engines they get most of their cubic inches from very long strokes. Some of these engines are very high RPM setups...

Shane

Well said. With the longer throw and shorter rod, you are plain and simply displacing more air. All else being equal, you will make more hp and tq throughout the entire rev range because there is more cylinder space to fill. There is no replacement for displacement. Power adders not included.

There were some tests done with some SBFs using E7TE heads. No porting. on a 306 cube, it did 306 HP. On a 331 cube with more cam, it did 350 HP. On a 393, with more cam yet. I forget the result, but it was way more than what AFR's formula said was possible. That flow x .257 x number of cylinders = max HP.
This debunks the theory that adding stroke to a combo with "maxed-out" heads can't find even more power.
If the cam and manifolding doesn't change, then most of your gains may well be "under the curve", but average HP will increase, for certain.

IMHO, its not as much about just the bore and stroke. Its the whole combonation that makes certian motors (I.E. Pontiac, etc) what they are. Head runner volumn, camshaft, compression, combustion chamber design, etc. Eric L

i agree, the rest of the motor is optimized to the bore/stroke and operating speed of the motor.

454 was always known to spend time at a higher rpm than a pontiac.

the pontiac was designed to have more torque than the chevy. the 5100rpm redline, bore/stroke, low engine speed efficiency of their cylinder heads, 3.23 rear gears vs. what you'd find in the back of chevelle suggests it.

What if the heads, cam, intake, exhaust were matched specifically for to maximize power in a 346ci LS1. Would adding the longer stroke still increase power, or could other setup (all things staying equal) be enough of a mismatch to the stroke that it offsets the power gained from more displacement?

Any displacement can be optimized for a certain rpm range by manipulating all of the mentioned variables. Bore/Stroke determine displacement. By increasing stroke and shortening the rod, you increase the distance between TDC and BDC, and thus the volume of the cylinder. Yes, you will gain power from a larger stroke with components optimized for the 346ci, because the limiting factor in optimizing the 346ci, was its displacement. You are not only increasing power by increasing cylinder volume, you're also increasing the potential to make even more power by optimizing it.

the fact is high stroke to bore ratio will have a harder time living at high rpm compared to a low stroke to bore. therefore the engine speed will usually be lower with large stroke apps.

the fact is high stroke to bore ratio will have a harder time living at high rpm compared to a low stroke to bore. therefore the engine speed will usually be lower with large stroke apps.

This is true, but most ls street type set ups are hydraulic cams so the valvetrain limits maximum engine speed more so then the piston speed.

2 engines with the same cubes and all else pretty much the same, but one with a longer stroke than the other will make more torque. My friend proved that with two different engines he built. Two iron 422ci's with the same cams, intake and heads on both. Longer stroked one....made much more torque. They only made within 10 peak HP of eath other.

My 4.125 stroke 427ci also made much more torque than any other 427ci that I heard of anywhere back in 2002 when it went together. And I have cheesy LS1 heads.

.

Adding displacement will make more torque in the lower rpm range which of course is more HP in lower RPM if all other things are exactly the same like the OP stated. Im definitly not buying the "more HP throughout the RPM range" statment. Adding stroke not only adds displacement, making it harder to fill the cylinder especially in the upper revs, but also the added piston speed creates more friction which is another tally against hp production in the upper RPMs.

Horsepower is a calculation derived from torque, which is in it's basic definiton is a measurement of cylinder pressure. Increase cylinder pressure over time and you increase horsepower.

the longer stroke gives more momentum to the rotating assembly.
how does this extra momentum effect acceleration of the piston what does that do to HP?

a longer stroke also gives more leverage to turn the crankshaft. how do you think this will effect the engines output characteristics.

More stroke = more displacement.

More displacement = more fuel and air.

More fuel and air = more power.

If you only change an engine to increase its stroke, it will make MORE power at ALL RPM. Period.

...

a longer stroke also gives more leverage to turn the crankshaft. how do you think this will effect the engines output characteristics.It is believed that the leverage effect is offset by the higher friction caused by increased piston speed (they cancel each other out).

So let me get this straight would you guys thinking stroke won't increase power on it's own agree that a 4.8l ls will make as much power as a 5.3l with the same top end parts and cam? Only difference between them will be stroke right:)

So let me get this straight would you guys thinking stroke won't increase power on it's own agree that a 4.8l ls will make as much power as a 5.3l with the same top end parts and cam? Only difference between them will be stroke right:)

If you increase stroke (and therefore displacement), you should make more power everywhere except peak power. The old cam and induction system will limit the peak power, but the displacement increase will make more torque (and therefore horsepower) everywhere else and cause peak HP to happen at a lower RPM.

There's a older thread where this was already discussed and elaborated more clearly, with some dyno results as an example.

Well I agree with you that power will increase. I really wasn't asking the question rather pointing out another example for others to look at. There was a post from a guy in the dyno section that just switched to a 383 from his stock ls6 and it did make a huge improvement in torque and still squeeked out a little more peak power at a lower rpm. This is with all the same stock ls6 induction parts. Granted it probably picked up a little SCR from the stroke.

My experience, same cam, similar compression, 346 to 383 was about a 35-40 horse jump in torque and horsepower across the entire powerband to about 5200 RPM. From 5200 RPM to 6200 RPM, the 346's horsepower began catch the 383's and they met at my rev limit of 6200.

That experience has been repeated over and over again.

Here is a very good example from an extremely old thread that will be hard to find from AFR. They posted it 4 or 5 years ago. I am glad I downloaded the pictures.

Same cam, same heads, 346 vs. 383 -??cc pistons, but similar compression ratio-
279055

Edit:
Notice that the statement made earlier in the thread that the powerband is effectively moved down is indeed precisely accurate. At any given time, "draw" a horizontal line and notice that the power made is between 300 and 400 RPM lower with the 4" stroke. It makes it a helluva lot of fun to drive, that is for sure!

My experience, same cam, similar compression, 346 to 383 was about a 35-40 horse jump in torque and horsepower across the entire powerband to about 5200 RPM. From 5200 RPM to 6200 RPM, the 346's horsepower began catch the 383's and they met at my rev limit of 6200.

That experience has been repeated over and over again.

Here is a very good example from an extremely old thread that will be hard to find from AFR. They posted it 4 or 5 years ago. I am glad I downloaded the pictures.

Same cam, same heads, 346 vs. 383 -??cc pistons, but similar compression ratio-
279055

Edit:
Notice that the statement made earlier in the thread that the powerband is effectively moved down is indeed precisely accurate. At any given time, "draw" a horizontal line and notice that the power made is between 300 and 400 RPM lower with the 4" stroke. It makes it a helluva lot of fun to drive, that is for sure!

I referred to that thread the last time this discussion came up.

...the motor that was previously in my car (the stock short AFR 224/228 combination you guys have read tons of info on) on the very same dyno I recently completed testing the 383 on, put down 550 HP / 482 Ft/lbs.

FIRST ROUND OF TESTING

Essentially the exact same combination as the 346 in my car and whose flywheel dyno results I shared with you above (550 HP/ 482 TQ), the ONLY difference being the larger 383 displacement shortblock.

Final Results 552 HP / 522 TQ

Summary:

The results were inline with what I expected...I was questioning whether the larger engine with the same induction/small cam might make less peak power and was glad to see it came in exactly the same. Big increase in TQ was a no-brainer.

I do think hidden somewhere in one of the post about the build Tony said the 383 was about 0.4 less SCR also though. Not that it would make a world of difference, but using the same cam the DCR will drop also.

I referred to that thread the last time this discussion came up.

I hope I wasn't stepping on any toes. I didn't see the last thread, just this one. :emb: I was actually trying to validate exactly what you were saying in your last post. :cheers:

Post 29 sums it up perfectly....Just wanted to throw one more variable in.
When stroke is increased and rod length stays the same, the rod to stroke
ratio worsens. Rod length affects piston dwell time (milliseconds) @ or near
TDC and BDC. Compression ratio limited stock car engines (usually 355 sbc)
make use of the longest rods possible not only to lighten the piston to as few
as 300 grams but to dwell (or stall) the piston @ TDC longer to build more
heat during maximum compression and ignition. Heat (literally in British Thermal
Units) is the transformation of potential energy (fuel source) to kinetic motion
So by increasing stroke, decreasing rod/stroke ratio, and accelerating piston speed @ TDC....the piston's increased change in direction while harder on the
wristpin actually pulls on the combustion chamber/intake port harder. Intake
manifold vacuum and port speed are dramatically increased.....both helping
throttle response and low rpm torque.......just say'n:thinker:

^^ yep. Super Chevy did a test (on an SBC albeit, but same concept). They had a normal 355 H/C package, dynoed that. Then took the same parts and put those on a 383 bottom end with the same compression ratio. I believe torque output passed the 355 at around 3K and the power curve did too not long after that

This test seems irrelevant since they ran the same compression ratio on both motors. you should see a higher compression on a stroker motor, because of increased swept volume. This test would be much more interesting if they had just changed the stroke and let the compression ratio be higher for the stroker motor. All they really did was compare how the heads and cam responded to more displacement.

All they really did was compare how the heads and cam responded to more displacement.

I'm pretty sure that was the point of the test; to see how an engine reacts to more displacement. Adding a second variable (like CR) to a test onlyskew the results and makes the test invalid.