Cab, its a 383 with 906 heads. I am normally running anywhere from 38-40 degrees of timing. I have a Unilite distributor locked out with a MSD digital 6, so it retards 20 degrees while starting. Last year the more timing I put in it the faster it went, Saturday however when I started up on timing it slowed down and I can see the denotation specks on the porcelain, so just trying to decide if those XR5 are too hot or if I simply need to bring the timing down or both.