SOMbitch

iTrader: (8)

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??

DONAIMIAN

iTrader: (18)

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

SOMbitch

iTrader: (8)

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.

Golf&GM

iTrader: (22)

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

Prorac1

iTrader: (4)

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

hitmanws6

iTrader: (20)

^^ 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

XtraCajunSS

iTrader: (2)

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

Golf&GM

iTrader: (22)

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?

slowride

iTrader: (3)

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.

XtraCajunSS

iTrader: (2)

Yes, you will still make more power.

Shane

disc0monkey

iTrader: (10)

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

Prorac1

iTrader: (4)

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

SleeperD

iTrader: (1)

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.

Isolde

iTrader: (4)

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.

disc0monkey

iTrader: (10)

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.

SleeperD

iTrader: (1)

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.

disc0monkey

iTrader: (10)

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.

slowride

iTrader: (3)

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.

LS6427

iTrader: (2)

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.

.

wht97ws6ta

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.