Quote:

isn't the single plane only good til 500hp?



where does this come from? i admit my engine is nothing outstanding and the car is light but a mild flat tappet 451 by a backyard hack running 162 mph with that (stock) manifold has to be doing better than 500. this is with <11:1 CR, rpm heads and a .585" flat tappet. what would it do with tweaked 13:1 roller and better heads? imho the m1 flange manifold goes to 650 with no extravagant measures.

as to the original question imho the rpm head fills more voids than ANY other bb chrysler head offered. with the right selection of parts this is a 600 hp head all day long at a reasonable price point, a minor cleanup/backcut would be beneficial