The factory rated that motor at 8.5 compression. I have found Chrysler's numbers to be very optomistic and it is probably closer to 7.5, since it has the stock pistons in it. The car belongs to my brother and I was trying to help him out. We settled on this cam because of the claims made on the website. According to Hughes website, that cam is supposed to build cylinder pressure and shouldn't be put in anything that has much more than 8.5 compression. It sounded like the perfect cam. Perhaps it is hyped up advertising I don't know, I do know that I'm rather disenchanted with the whole fiasco and probably should have gone with much less duration but similar lift.