So I see peopel are selling 243 heads for LS6 and LS2. Now I can see the basic casting is the same but what about compression ration? If LS2 6 liter runs the same combustion chambers as LS1 5.7 lilter wouldn't it be too high for LS2? So I guess my question is what is the chamber size for the 243 heads for LS2? or may be LS2 pistons are dished?

 

Both the LS6 and LS2 share the same cylinder head. Only difference is the LS6 used sodium filled valves. LS6 has 10.5 comp. ratio and LS2 has Approx. 11.1. Combustion chambers are also the same size. The 5.3 litre in the Gran Prix is also a 243 casting.

 

I see, so LS2 does have higher c/r

 

Due to flat top pistons that the LS6 does not have...

 

243 castings all have the same chamber size, so they will all give the same CR on same motor.
LS2 has a higher compression due to it's different bore/ piston size than the LS6, not because of any head differences (valves).