Difference in Y's
 

How much of a difference in performance would there be between the Flowmaster Y(Dual 3" inlet, 3.5" outlet - needs 3.5"-3" reducer, and the magnaflow Y(Dual 3" inlet, 3" outlet / No reducer needed)

I'm sure everyone knows what the flowmaster Y looks like, heres the magnaflow:

http://magnaflow.com/02product/hardware/gifs/xypipe.jpg

the flowmaster has a smoother transision, and is most probably cheaper.
the magnaflow just seems to "jam" together right there... however, i dont see there being a huge HP gain, but it looks like you are building a custom y...

for reference sake, here is a custom Y w/ the flowmaster
https://ls1tech.com/forums/attachmen...chmentid=41443

techincally there could be a big variance. However the exteriot has little to do with it. It's more to do with 'how' the Y merges the flows and enhances the scavenging effect.

To make it easier to understand, if you think about it a H pipe is really just an X with a large center section, but this means that where the two pipes join there is only a small cross section. On a true X the teo pipes will run paralle with each other giving a larger cross section where they are essentially one pipe.

A Y has similar properties and needs to be designed as such. The downside is the better flowing merge collectors are physically larger and take up more room.

HOWEVER

Unless you are building the ultimate exhaust system it really won't make any odds. What does a few (like 1-3hp) difference really make on a 400+bhp road car.

- ANSWER = very little.

On a full out cometitive race car then yes, every single pony is important.

Go with the flowmaster y merge. Never seen anything anyone run numbers with the magnaflow x.