I still think it`s funny about this debate. I`m not one to say dual pattern cams don`t work, they do and they do well as do single pattern grinds. However, When a exhaust system has headers, ample sized pipe, low restriction mufflers, why is the need there for more on the exhaust side?
Every chevy head I`ve ever looked at has a good exhaust port, it`s the intake side that`s not that great, when you look at a ford small block windsor head it`s just the opposite, the exhaust port is small, kinked, and looks like a nightmare, you wonder how the engine breathes at all, the intake port is big and with some work flows nicely, in some cases the port is too big like on the boss heads. But as for a example on a sbc, my opinion is simple, a dual pattern cam is needed when the exhaust system is not altered from stock or when nitrous is used, when the exhaust is free flowing a single pattern fills the bill, when the exhaust is already free flowing and a dual pattern grind is used I agree with Johnsongrass, over scavaging the exhaust kills the torque.