[Jay S]

Most D ports don’t go turbulent until about .5” lift, especially when you bolt the intake to the heads. While it is true a stock D port doesn’t gain a lot of flow after .4”, most all Pontiac’s respond positively to more lift than .407”.

Extra dwell on a cam that has the same low lift durations as another cam is the result of trying to get more area and limiting the cams lift. There is a point where the cam profile has better harmonics with more lift and less dwell.

Some cams have .2” tappet lift duration ratings. Generally if 2 cams have equal lift and durations at .050”, the cam with the larger .2” duration will make more power. Unfortunately that is pretty unknown on most stock cams. That file Stan had of a Crane 041 Blueprint was showing 140*. A Crower RA4 60919 has around 134* @.2”. I don’t recall exactly what a Melling SPC-8 has @.2”, but I think I recall it’s .2” duration it is closer to the Crower version of the 041 than the Crane.

The 068 variations may not vary as much as the 744 and 041 in how they are ground. Would be interesting to compare some cam DR files for the various 068 copies.