390 Pistons

[ted]

Originally posted by Dwight


Using the H heads and a 390 crank, How much has to be removed from the head to increase the CR one point? Two points?
THANKS DWIGHT

DuckRyder is real close on his amount as 10cc per full point in compression is indeed a good rule of thumb for that particular bore and stroke combination. The actual math for a stock 390 figures out to 9.12cc's to raise the compression one full point. As far as milling the heads, the H heads should need 0.006" milled for each cc removed. For 10 cc's, you'd need to mill the head 0.060" to get your full point in compression increase. I'd also suggest cc'ing the heads end to end though to insure the heads are equal across the chambers. It's not unusual to have one end having larger chambers than the other and this is easily compensated for when ultimately milling the heads as you'd just have the end of the head that's got the larger chambers milled deeper than the other end so that when you're through, both ends have equally sized chambers.