Well with our class restrictions, i would say he was running out at around 6200 and thats being generous. I think the bigger worry is keeping the intake air cool, and that those big long runners act as a heat sink. We find with our victor junior and one inch spacer that having good cool intake air and painting the underside and runners of the manifold with ceramic heat insulating paint it gives a slight edge,but i must add that the scutineers are frowning.