Hi keith, Been chasing the same info, myself, the last few days and have found several pieces of data that state: the early heads, 68-70, have a chamber volume of 68cc s 71-74 are 72cc, and 75-76 are in the high 80cc range, (89, I think) so I would guess your compression increase would be in the .1 to .2 range would would net a couple of horse power. see ya, tom.
