Doug G

Stock LQ4 bottom end, LS3 heads shaved .050, 4.030 x .051 gaskets = approx 10.5XX:1 compression ????

3pedals

iTrader: (3)

Doug I have never actually measured the piston top of an LQ4 piston, so its tough to be accurate, but I think it will be 10.8 - 11.0:1 ish
Of cousre this depends on exact deck height, and exact valve releif sizes, as well as final cc of the heads.
-A .050" cut should take about 8.3ish cc's out of the heads
-pistons are generally about .007-.008 out of the hole, but they are dished, and probably come close to equalling a zero deck flat top piston. - This is a guess.
Personnally, I think if the gaskets are truely 4.030, and you cut nice generous .080" valve releifs(so you can change cams and degree them where you want), you will be right at 11:1 - PERFECT for a pump gas warrior!

Prorac1

iTrader: (4)

I dont like the idea of running a 4.03 gasket with the LS3 heads. IIRC the combustion chamber requires a 4.06 bore gasket. Unless im wrong? Refresh my memory Barret, lol. Eric L

Prorac1

iTrader: (4)

I also agree on flycutting the pistons just because. It REALLY opens up your possibilities for cams and such. I flycut mine a hundred thou on the intake side only. I had PLENTY of clearance on the exhaust. Eric L

3pedals

iTrader: (3)

I used a 4.00x .040" cometic gasket with mine, to squeeze the max compression I could get. Seems to work well. The bore on mine is 4.00" so even if the gasket hangs into the chamber, so does the actual bore

Doug G

Gaskets are in....just looked them up.

Bore (in) 4.080 in.
Compressed Thickness (in) 0.051 in.

I was informed I needed the LS3 head gasket, not the LS2.

3pedals

iTrader: (3)

I have not looked close at the OEM GM gaskets, but the need for the LS3 gaskets may be due to the design of the oem gasket its self and the placement of the sealing ribs?
My 4.00" Cometics are sealing good.

Montec984

iTrader: (2)

Here is a really nice compression ratio calculator. Also, I know personally that this guy is a camshaft GENIOUS! No cookie cutter cams here!
http://www.buyracingparts.com/compre...alculator.html

Doug G

Sooo.... using the numbers below (not taking in account the VR's to be cut) I'm getting 10.44:1 cutting .050 off the LS3 heads.

In all my searching I keep coming up with some very close numbers...Someone on another site had measured theirs and had posted these numbers ... I lost who it was and can't give credit
Anywho...might want to sticky these numbers ?

Here are the factory specs of an LQ4:
4.000" bore
3.622" stroke
6.098" rod length
1.338" comp. ht. pin location
-6.7cc dish piston
71.06cc chamber
0.051" gasket thickness 4.010" bore
9.24" block deck height

LS3/L92 heads are 68.5 +/- 1cc

3pedals

iTrader: (3)

Good work Doug.
I have to question how the piston dish volume was calculated? Most pistons would be measured and calculated to zero deck.
we all know the raised portion of the piston is actually about .007-8" above deck height as assembled, and so the actual dish volume would be substantially less, and part of the piston will occupy chamber volume making it less as well. resulting in more CR than thought.
If you have taken ALL this into consideration, then AWESOME, because I am way too busy to measure it to get the exact numbers!lol
Barrett

Doug G

IF I could find where I found these numbers by who posted them and ask

Doing the math (rods,piston comp height,stroke) I got close to .008 (had to guess on rod length subtracting bearing journal)