I believe both the LQ4 and LQ9 stock heads have 72cc chambers. The L98 heads are around 58cc, IIRC.
So, maybe a 1.5 point increase.

 

So would you happen to know how much the compression would be bump'ed up by running the L98 heads. I'm not sure what 14cc less would work out to be. anyone??

Thanks Kyle

 

ls1tech.com should help you out.

I believe most those pistons in these LS motors are just flat.

The deck heights I think are all over the place...sometimes the pistons even stick out of the hole on the factory motors....

Just need to research those sites.

I'm going to guess that you are going to be around 11.5 to 1.

 

Think hes referring to a 305 Gen 1 motor wanting to use L98 heads?
LQ4?

 

LQ4 has dished pistons and were in trucks of all sorts. LQ9 has flat pistons, hence the comp difference and were in escalades and silverado SS trucks. The stock heads on both are generally 317s and I think they are 72cc.
LQs are 6.0L Gen III motors.

 

do you mean L92 heads?

 

yeah, that's it the L92 newer style heads. sorry about the mix-up

kyle

 

http://www.ls1gto.com/forums/showthread.php?t=286447

i dont remember wehre i got this from, but i know i got it from ls1gto.com but i kept it in a word folder..

3. When bolting the L92 heads onto a LS2 without any milling, what does the compression drop to?
The L92's 70cc combustion chamber would drop the compression ratio to ~10.2:1, assuming you use head gaskets of stock thickness.

1. I've read that the L92 head needs to be milled to retain stock LS2 SCR (Static Compression Ratio) of 10.9:1. True? If so, how much?
True, The L92 heads need to be milled .030 to maintain stock LS2 static compression.

Stock: 70cc
-.010: 69cc
-.020: 67.5cc
-.030: 66cc

What does this mean? It means on an LS2, you need to mill the heads .030", and run a .055" gasket to keep 10.9:1 compression. the stock LS2 heads are 65cc, and the stock gasket is .060" (im pretty sure on that gasket, but someone correct me if im off). With a stock .060 gasket and 66cc milled L92's compression is 10.77:1.

I believe the compressed thickness on the stock LS2 gasket is .055. LS7 gasket is .060. The same head gasket is now used for both the LS2 and L92.

stock LS2, unmilled l92's (72cc), .055 gasket= 10.17:1

with a .030 gasket, 10.78:1

You also then have a Piston to head clearance of just .020", as most pistons are .010" out of the hole from the factory. Thats an awful tight squish area, and will hurt power and emissions.

In short, mill the heads.

63cc's on a .045 gasket gets you 11.61:1. 66cc's on .045 gasket gets 11.1:1

with the l92's being a thin deck, im not sure id go down too far on them. .035" of squish is acceptable.

I never milled one down far enough to say for sure, but 63cc's would be a .040 mill, maybe .

the LS2 is basically the same bottom end as the LQ9.. LQ9/LS2 both used perfect flat top pistons, as the LQ4 used dished pistons..

aaron

 

Thanks for all the great info guys.

Kyle