Vic, I think a lot of it has to do with the valve job/port design you do. Flowing good the right direction without flowing good the wrong direction. But then that is probably easier said than done? Even with 104 degrees of overlap @.020 and too small of a header,no signs of reversion on the 421. It took too small of a camshaft with very little overlap(too wide of a lsa) and late exhaust timing to show any signs of reversion. Keith
