To much compression!!!
The only difference between the LQ9 and LQ4 is the pistons. The LQ4 has -6.7cc dish in them and the LQ9 has the same flat top piston thats in the LS2's (Depending on what year LQ9). The early LQ9 may have had pressed pins much like the LS1's and the newer are floating pins but both rod's and piston heights are the same whether it's floating LS2 style or pressed LS1 style. The LQ9 will have the same compression as an LS2 with the same heads.
Stock compression ratio's for LQ4 are usually advertised as 9.4:1 when in all actuallity it is 9.57:1 when calculated. The LQ9 stock calculated is 10.29:1.
LS2's calculate to 11.12:1 compression stock which have 243 heads measureing 64.45cc chambers compared to the LQ series 317 casting heads 71.06cc chambers. The LQ9 with a stock head gasket and a stock 243 head will have the exact same compression as an LS2 does which is 11.12:1.
LQ4 with stock 241/853 LS1 heads would be 10.03:1
LQ4 with stock 243 heads would be 10.27:1
LQ4 with stock 5.3L heads w/ 61.15cc chambers would yield 10.67:1
All of the above is calculated using a stock .052" head gasket thickness.
