LS1LT1CAM

thinking of putting a 4.8l crank in a 6.0l (330cu in) with 72mm turbo

squee

iTrader: (16)

Why on earth would you want to do that?

LS1LT1CAM

limited to class rules 72mm turbo
550 lift cam
220cc intake
smaller motor thinks the turbo, cam, and inatke size larger
flow numbers for turbo better on smaller motor if maxing out turbo
need to make 1000 flywheel and run 8.70 at 3400 lbs on bfg 275/60 radials

nobreaks254

iTrader: (50)

You need a crank?

drz

iTrader: (3)

Under what circumstances exactly does a motor make more power with less displacement???

rhubar

iTrader: (10)

better rod ratio. Also, you can turn faster rpms with a shorter stroke. I don't think the idea is practical because the crank, rods, and pistons will have to be custom depending on how detail the build is.

StrikeZero

iTrader: (1)

I'm thinking about this as well (no turbo for though). Could move some air with that 4" bore

And I get a weight break for running a smaller engine. . . hehe

But this is more for Autocrossing. . .and not dragracing.

drz

iTrader: (3)

When has this ever been the case? Rod ratios and rpms don't make up for displacement. Period. When was the last time you saw someone DE-stroke for power?

Since I don't know what kind of racing or under what class rules the OP intends to run, I'll try not to speculate on any rules he hasn't yet mentioned. I find it hard to imagine that the engine displacement isn't subject to some form of restriction or penalty, so the OP must be considering a motor smaller than the class rules allow. The only case where a smaller motor might be faster is when it is given a weight break.

But generally speaking, if a motor is to be restricted by turbo size, it's most effective to run a motor as big as you can get away with. The lower the rpm and the lower the boost you can max out the turbo with (think restrictor), the more efficient the motor will be and the more net power it will make. Smaller motors that must run higher rpm and boost to push the same amount of air will be handicapped with higher friction, higher exhaust back-pressure, and higher thermal losses.

66deuce

iTrader: (1)

it's not a crazy idea..Sprint Cup motors run somehere around a 3.25 stroke.(tho the bore is huge)
there are hp gains from a shorter stroke due to the pistons/rings not moving up and down in the bore as much,compared to a longer stroke motor..this means that the motor has to be spun higher to make the big numbers..

rhubar

iTrader: (10)

[QUOTE=drz;10462224]When has this ever been the case? Rod ratios and rpms don't make up for displacement. Period. When was the last time you saw someone DE-stroke for power?
QUOTE]


Well i've never seen this first hand, but if you ever get a chance to look up a engine builder by the name of Henry "Smokey" Yunick you'll find he has built some crazy horse power motors with shorter skrokes and higher rod ratios.

I understand the saying "there's no replacement for displacement", however there are other build formulas for making big hp.

novaflash2002

iTrader: (51)

This is true to an extent. lets compare a 383 (350block with a 3.75 stroke) and a 377 (400 with a 3.48 stroke). Depending on the rpm range the engine will make way different power between the 2. a 383 will walk a 377 under 5000 rpm, but when you get that 377 humming above 5000 rpm it will rape that 383 in hp and tq. depending on the racing he is running, if you are drag racing, lanching at 4000 rpm the 377 in theory will move the car down the track faster. also with that big bore, it allows the air to move by the valve into the cubustion chamber easier, even though the 377 has less cylender volume. i know the term is (there is no replacement for displacement), but why will a 400 beat a 454?

Chrome355z

iTrader: (1)

Because whoever built the 454 didn't know what the **** they were doing...

ttranssam

iTrader: (10)

geez keep this going i wanna see the out come, ive heard about de-stroke but ????

novaflash2002

iTrader: (51)

Lol not the answer i was gonna put, but good one.. Its not always the displacment that wins race's. Its the effiency of the used power, or average power.

427

iTrader: (3)

If no rules are guiding your choice, you would be best served with the largest engine that is of sound mechanical design.
That being said, I have built class engines that used a shorter than stock stroke and ran very well and if the guy that made the original post wants a smaller engine I say have at it!!


Kurt

racer7088

The bigger bore is helping them make more power not the smaller stroke. The stroke is smaller since they want the big bore and are limited in CID hence the smaller stroke.

drz

iTrader: (3)

I thought it was already clear we were discussing stroke independent of bore size.

I'm sure you'll agree, increasing the stroke to 4" from 3.75 in the 383 would make more power than the original 4"x3.75" configuration (ignoring rod/cam complications). Similarly, a 4" crank swapped in the 377 would also make more power. Conversely, a 3.25" stroke crank would cost both motors power, even though you might be able to spin them to the moon (assuming the valve train is up to the task).

In any racing class where displacement is free or only lightly penalized, the front runners will not be leaving any displacement on the table. In any racing class where short-stroke motors are favored over much bigger motors, it's only because displacement is heavily penalized, usually by vehicle weight or intake restrictors.

racer7088

Smokey Yunick liked longer rods but never recommended a smaller engine over a larger one just to have a better rod ratio. We all asked him at PRI and he even got mad that people thought you could make more power with less inches but a longer rod. He just liked longer rods but even said that with today's heads that wasn't even any firm rule of his any longer.

Smoky also noted to the guy that asked him about destroking for power that they had all cheated by building larger engines than were allowed including Roush and many in NASCAR but no one ever cheated by building a really small motor !!!!!!!! (with super long rods) .........enough said.

Dan Stewart

Katech already answered this for you in the Advanced Engineering forum in a post by someone else looking to build a destroked ls...check there

But, instead of de-stroking a 5.7L or 6.0L....

just buy a 5.3L......since it is just under 330ci

as for the in-depth discussion on rod ratio, etc......

We all are forgetting one small problem to overcome in using this theory to gain high rpm power........

the LS series can't spin that high without puking it's parts all over creation without easily spending well over 100K in research and fabrication to make it there.......

BlackScreaminMachine

iTrader: (17)

I completely agree, I have spoken to Erik YEARS ago about pistons and how they correlate in Indy cars, quite interesting.