My buddy has a '99 SS, stock shortblock, AFR heads, & a stealth cam.
He spun a bearing and needs a new shortblock.
We can get a LQ4 short block for a good deal.
I know that his CR will drop with the dished pistons of the LQ4.
Would using a cometic gasket be enough to negate the CR drop? If not, how much should the heads be milled?
Car doesn't have to be a 13:1 motor, just want to mitigate the power losses due to compression to take full advantage of the larger stroke.

Thanks, your help is very appreciated.

 

if im not mistaken ....the compression shouldnt drop.... i could be wrong so dont hold me too this but i know on my stock ls1 when i switched to the 317 head it took my compression from i believe 10.0:1 to 9.5:1 and a lq4 comes stock with 9.5:1 with the 317's so with that bieng said if you put ls1 heads on a lq4 your compression should be 10.0:1 i would think???

If thats right then whatever your friend has with his setup now, when he switches to the lq4 (if he does) his compression should stay about the same, or close enough.

again, not 100% sure.

 

He's taking his heads which are currently on a LS1 block and will be swapping them onto the new LQ4, so the compression will drop I know that, but how much I am not sure.

 

But what im saying is i dont think it will.

The lq4 has a dish but it also has a way bigger piston so the dish is needed to keep compression down.

if you took and lq4 and put true flat top pistons in it like and ls1 has, and then put ls1 heads on it youll have MORE compression then a stock ls1.

 

The 6.0L engines have larger 72cc chambers, so the smaller chambers on the AFR heads should make it up. 64cc chambers should put the CR around 10:1.

Also, LQ4's and LS1's have the same stroke (3.622"), but the LQ4 has a larger bore.

 

Read this, do the math, let us know what you get.

How to Calculate CR-Car Craft Magazine

 

Seems like we might be able to find a LQ9 instead. That would be even better. I guess it will be at ~10.5:1 depending on gasket thickness. Do you guys agree?

 

That would seem right to me. lq9 with his same heads he should have more compression then he does now, and more cubes, be more power for sure

 

i would try to get an ls2 and not dick around with it. and i personally prefer an aluminum block.

 

Hey, i'm about to go with an lq-4 motor (long block) with a front mount t-76mm turbo and the epp forced inductions cam, seems to be like your setup. How's your car performing? Mind you, i'm new to this stuff.

 

^^^ if you have an FI setup i would not raise the lq4's compression ratio.

 

Ill let you know in a few days

 

Yeah but the price is like 1500 extra...no thanks. the weight difference is not worth the extra money.

 

i prefer the cast iron blocks, mainly the used ones. a brand new block distorts, after its been through a few heat cycles they dont distort nearly as bad and hold tolerances better. aluminum blocks are okay, but there is always a chance of splitting a sleeve. from what i have found the dish in a lq4 piston is about 7cc's. the piston sets about .003 out of the hole. the comression is 9.41:1 from the factory. so if you put your 64 cc heads on it with a stock gasket of .051 thick the compressed and a 4.045 bore on the gasket and a 4.00 bore on the block the compression ratio would be 10.22:1, just a hair above what a lq9 is.

 

I prefer my Iron Block..

 

good point about the old blocks not distorting as much as the new block would. if an aluminum block is done properly it will hold up just as much power as a iron block would. yes it would be more expensive to achieve the same goal but you also get more benefits.

 

What benefits besides weight savings?

 

about 50lbs, and it might disapate heat just a little quicker.

 

weight and it should disperse heat better. also less weigh means the front of you car can lift easier which means that the weight gets transferred to the back and that is how you get traction.

 

Yeah, but in a car that is not an all out race car, either one will do fine...