I am taking my 4.8 to a 5.7 using stock ls1 crank and rods/pistons. I have 862 heads. What kinda compression will the 862's give me on a 5.7? to much im sure for boost. i want to run 10-12 psi. should i just get some 6.0 heads or try to find some 243's? any suggestions or criticism would be appreciated. im also on a budget, so i think the 6.0 heads would be the way to go if i cant run the 862's.

 

LS1 pistons are flat top and the 4.8 heads have a small cc chamber.
this will give you a high compression.
if your going to run some boost, use the 6.0 heads, they have a larger cc chamber
to lower the compression down just below what is normal for a 5.7 LS1.
Also the 6.0 heads use the same port size and valves that the 5.7 heads use.