how much does sound very when going from a 2 1/2 to a 3 or vice versa. or is the sound pretty much the same no matter how big your pipes are? im asking this becuase i need to know whether or not to get the 3" 80 series flowmaster or the 2 1/2 any suggestions?

 

The sound will get louder with 3".

 

will it matter if the ypipe is 2 1/2 and the muffler is 2 1/2 but the I pipe is 3? i ask this because i cant get a 3" ypipe for my headers.

 

Any restriction in the exhaust will hurt the sound, the size of the y-pipe I wouldn't think would hurt sound, only performance, why not get a local exhaust shop to fab up a 3" y-pipe.

 

You could get an exhaust shop to make you a y-pipe. I know when I get my headers the place I am going to is making a custom 3in y-pipe.