[thespud]

4-2-1's are useless really, unless you got 2 cat converters, then go to one. Gives you slightly (VERY slightly) more power if you do it that way.

 

[Flashmn]

4-2-1 has its advantage, one of which is the fact that if you hit the downpipe on something, you can replace that part of the manifold, instead of the whole thing.