I agree with bjuice..but I went from a stock factory square port head with 2.19 valves to a -2x brodix(340 cc runers and 2.30 valve) and actually improved in the 60'. went from 1.35-1.36 down to a 1.31-1.32 and picked up 2-3 tenths in the eighth. That was with a 540 inch motor so it was under-headed with the 2.19 factory head...not sure what the runner volume is on those I have been told around 290-300