I did an SOHC intake comparo years ago, and that intake out-performed the factory 2X4 dual plane from 5500 on up. I also had a Munro 2X4 intake, which was better than either of them between 5500 and 6500. The single 4 intakes were down significantly on power, but I got one from John Vermeersch that had been converted to a Dominator flange, and that one was 50 HP better than the other single 4 manifolds.