Guys, i put a set of hedman shorties on my car, and they came w/ a y pipe that was nasty, 2- 21/4" into 1 21/4",,, not the hedman piece,,, it was all used.. now i wanted to go 2-21/2" pipes into one 3" single, to a 3" cutout, then reduced to 21/2" all the way back.. well... the exhaust shop tells me that they can only fit 2- 21/4" to one 21/2", to a 21/2 cutout.. doesn't seem like it'll flow too good. but what do yall think?

 

I think you need to find another shop.

Stock, the pipes were 2-1/4" to 3" to the cat, then 2.75" to the muffler.

I've heard varying stories about the Hedman y-pipe, but it is at least 3" at the cat (although I hear it is 2-1/2" just before the cat - I haven't seen one in person). A high-flow direct-fit cat for your application is 3", and any aftermarket cat-back for it would be 3" as well to the muffler.