I was going on the info that the 317 heads will lower my compression ratio over the stocker 862. But since i came across the head casting info put out by JRP, it showes different. I see that the all volumes and diameters are bigger on the 317 which is what I want for more flow. but the 317 has a c/r of 10:1 versus the 862 with 9.5:1. The statistics info I was told was wrong. I want the 317's for better flow so what will I have to do to lower my c/r for boost?

 

The 317 heads have a 72cc chamber and I beleive the 862 heads have a 65cc chamber.The 317 heads used on a 5.3 block will have about 8.7 to 1 compression.

 

862s have a 61cc chamber. There are many more variables to SCR than just chamber size, although it does play an important role. All other things remaining the same, replacing a 862 head on a 5.3 with a 317 head (larger chamber volume) will drop the CR like whitt1 said.

 

thanks guys I just wanted, to reconfirm thats all. I have all the statistics on the heads but wasnt sure how the c/r drops and now I know