On the Camaro system they have advertised with the 3 inch pipe to muffler and then the transistion to 2 1/2 . Can I buy any direct fit muffler with a 2 1/2 inlet and it will work?

 

yes. that kit is a dynaomax kit. i used a hooker aerochamber muffler in place of the dynomax muffler when it rotted out. have it welded in and you might have to trim the driver side pipe down to get it to look right with tips poking out from the bumper.

 

If you're talking the same system I'm thinking of, it is a Pacesetter system, not Dynomax. And, the I-pipe is 3" all the way to the muffler, and it's the muffler itself that goes from 3" to 2-1/2". Therefore, 2-1/2" replacement mufflers will not fit it, unless you have the inlet expanded to 3" ID.