The victor Jr. Manifold is pretty sweet, not sure however what the rpm range is, but it should work good at 4000, I'd imagine. Oh , and stay away from the edlebrock performer carbs, I know a lot of people that have had a lot of problems with them after a while. One guy I knew had a mustang and the thing screwed up from the inside and caught on fire....... didn't do much damage other than the carb, however.