[Greg Reimer 7376]

Aubrey-- I put BBC valves in the 3814690 409 heads a long time ago.I still have the complete engine I did it to. Trim your guide bosses for a positive type seal(no O ring ),install a 2.19" BBC valve,use a BBC stock eliminator type spring,retainer and lock, then use a 1.72 BBC exhaust valve.A 427 3/8' pushrod with a stock rocker works on the intake, and the 409 3/8" pushrod for the exhaust will put you in the infield of the ballpark.There is a century or two of stock eliminator engine building experience on this forum trying to help you, we all like your car and want to see it absolutely fly. It does sound like your cam is about 6 degrees retarded. You need about .060" minimum P/V clearance on the intake, and .090-.100 on the exhaust.More spring tension on the exhaust will eliminate the bounce. If the engine goes flat above a certain point, I would blame the exhaust springs, if it putters through the intake, then that's the one with the low spring tension. Also, dyno results don't always carry through to the track. The best dyno is the drag strip.