2.5" vs 3" pipe size for high powered FE; which is better?

[DuckRyder]

Provided you get mandrel, bent 2.5 will be fine.

Unbelievably there is only one exhaust shop in Atlanta that has a mandrel bender, the odds are probably better in California...

If for some reason you cannot find a shop with a mandrel bender then go with 3" compression bends...

[Jake11]

Bigger is better. Just have to have the ability to jet the carb for less restriction. Open headers? Is that too big.

[My427stang]

I would just match your header collector size.

Exhaust pipe sizing has become a bit of a hot rod and internet myth.

Primary pipe sizing is a very critical dimension in the exhaust, meaning primary header tubes. Based on the size of that tube, (and cam timing) it determines the amount of negative pressure being put in the cylinder during evacuation.

That pulls additional air/fuel in during overlap. Now of course collector design has a play in it too, but once you get past the collector, it's not nearly as critical, I'd even say past about 16 inches after the collector, it doesnt mean anything

If you run a 1 3/4 primary into a 3 inch collector, run 3 inch, if it's a 3.5 inch collector, I'd run 3 inch because 3.5 would be too hard to fit in there.

If its a 2.5 collector, run 2.5, it will flow plently if mandrel bent too.

Bottom line, the exhaust pipe after the headers is nowhere near as critical as the header sizes, and those will already be worked out for you. FYI, I am not making the power you are with my 390, and I have run 3 inch, 2.25 and 2.5. This time it will have 3 inch again because I eventually plan to put the 489 out of the Mustang in it.

No difference in low end on any of the combinations over the years