One of the reasons for the clifford to have run better is the Lump ported head. If you wanted to do a better/fair test try it with out a lump ported head.
That's a great point as when I ran my tests w/the two manifolds,w/just the adaptor plate, I also tried using 1" open hole spacer,1", 4 hole spacer,2" open & 4 hole spacers.
I did not have any lump ports.
MBHD
