Obviously bigger is not better...The size depends on a lot of variables, engine size, rpm range desired, etc...No set answer, if there was they would only make about 3 sets...We had an iron 377 with DART heads and it liked 1 5/8" stepped to 1 3/4" now we have a 422 SB2.2 and they are 1 7/8" stepped to 2"...you are going to have to come up with a lot more info...
We always used straight 1 3/4 or 1 3/4 to 1 7/8 step on a 355 ci with world product heads and lg port vortech heads Bigger will kill your bottom end in the motor.
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