Need to put an exhaust under my 5.9 I was wondering if diameter matters a lot? I have a magnaflow high flow cat I just got but the outlet is about 2 1/4... does that mean I need a muffler that's 2 1/4? IS that big enough for the engine? IF I did get a muffler with a 2 1/2 inlet could I adapt the cat to the muffler? Sorry, don't know much about exhausts..

 

Yes, if you go to an exhaust shop they will weld on the adapters. If you want good flow with a couple extra hp gain, go with a 3" muffler and pipe. Unless you don't want all that noise you can go with 2.5"