exhaust

how do i determine what type of cam(single pattern or dual)so i dont over scavenge the exhaust??

Determining whether you use a single or dual pattern cam is based on head flow bias between the intake and exhaust ports. If the exhaust port flows over 80% as much as the intake port a single pattern cam is for you. If it flows 75% as much as the intake port, or less, a dual pattern cam is best. Very basically, the less the exhaust port flows in percentage when compared to the intake port, the more exhaust duration you need for proper scavenging. Engines like 4V Clevelands, 429CJ's, and regular 429/460 engines have particularly bad exhaust port flow when compared to the intake port and unless this is improved by porting, these engines need a dual pattern cam with lots of extra exhaust duration. Something in the neighborhood of 12 to 15 degrees can be very benefical along with a little wider lobe seperation angles than would normally be used so that the exhaust port is opened earlier and the overlap numbers still remain the same.

my intake flow is 309 @ .700 and exh is 209 @ .700 that would be less than 80% ???

but my intake flow with manifold and webers is 246 @0.700 lift and exh is 209 @ .700 so that is more than 80% so do i go on head alone figure or do i go with manifold carby head figure???