necking down after collecter?

AJ/FormS said

Not the popular opinion, but I don't think there is such a thing as too big in that distance from the merge to the mufflers. One 3" pipe is similar in area to two of 2"pipes, but 2 of 2" pipes has ~33% more pipe skin... so if you installed a PAIR of 2s on each side, you'd end up with a lot pipeskin,er radiating area, and your muffler would not have to work so hard. lol. But I'd run about a foot and a half of merge-sized pipes first.So then.............

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While a 3" pipe has about the same area as dual 2" pipes,dual 2" pipes will not flow as good as a single 3".The reason is simple, anytime you have air moving over a surface the air in immediate proximity to the surface doesn't actually move.The air "sticks" to objects, Its stationary at the object but moves faster the further away from the surface.This is known as a boundary layer.In the case of duel 2" pipes you have 33% more surface area for air to interact with and form a boundary layer.So instead of the air through a 2" pipe it acts as though the pipe is only about 1.5" because of the slow moving or turbulent boundary layer.A single appropriately sized pipe will always make more power over a duel setup with the same "area".Not to mention a single exhaust system weighs less than a duel exhaust.More power and the overall weight of the car is lower,thats a win in my book.