[72LuxuryLeMansLa.]

Originally Posted by Dave Bisschop

Good question and while I'd love to tell you I have some magical formula that I use the reality is all my knowledge in this area has been from trial and error testing on the dyno. That being said using the Wallace calculator (Thanks Steve for posting the link) the old SP cam shows 64 deg, new one shows 61, OF on a 112 is 73 and the OF on a 114 is 69. I haven't done a manifold vs. header test with the new version of the SP, but I think it's safe to say it will work well with the RA manifolds since the old version the most we ever saw on the dyno back to back was 8hp less with the RARE GTO 2.45 manifolds vs. a Hooker SC 1 3/4" header. We had a 491 on the dyno a number of years ago with a set of our 300-305 KRE D ports, Performer RPM etc. with the OF on a 114, the engine made 567hp with the manifolds and 582hp with the headers, previously we'd seen a good 30hp spread comparing headers to manifolds in another engine we tested with the OF on a 112. So looking at the data I'd say when you start to go beyond 70 deg. overlap using the Wallace calculator the hp difference is going to get into the 20+ range quickly as the overlap increases. Under 65 deg. and the difference is more like under 10hp. Years ago we did a manifold vs. header test on a iron headed 9.5 to 1 467 with an Ultradyne flat tappet cam 263/271 @ .050 on a 112, the manifolds killed 45 hp at peak and 75hp at 6000rpm, using the .020" rated duration numbers the overlap calculates to 76 deg. I think this gives a general idea what to look for when deciding if a cam is a good choice to run with the RARE manifolds.

Got it. Thanks Dave, great info for the board!