I was under the impression that you needed an "f4" exhaust if say I want to do a swap. However, my buddy with a 96 750 Gixxer just took off his Yosh pipe (he thought it was too loud) and threw on a random V&H's pipe that his brother bought for his bike but did not fit (did not fit his brothers bike). By random I mean it could be for any bike, he has no clue. Now I have the opportunity to put his Yosh on my bike.....is this a bad idea? What determines if you can use the pipe....does it just have to fit on the midpipe and then good to go?

 

I guess you can give it a shot, cause the mufflers job is to lessen noise which in advertantly restricts flow. So anything "to me" is better then a stock muffler. If it fits, does not affect engine performance and does not leak I'd say your good to go.
However if you you notice your headers are glowing red at idle, I'd give it second thought.

 

If you're just swapping a muffler and it fits on the pipe, then yeah, give it a shot.