I just bought a new Flowmaster muffler with 2.5'' diameter inlets and outlets. I thought the stock pipe size was 2.5'' but it seems that its 2.25"? Is there a way that I could increase the outer diameter of the pipes by a quarter inch?

 

You could have someone fab a step-up piece, remove an equal lenth piece of the old 2-1/4", then weld it in place. Or you could use this opportunity to replace the rest of your exhaust. I'd honestly get with a muffler shop and they'll tell you what they can do and what your options are- they might be able to flange out the end of your pipe to the proper size at minimal cost.

If all that seems too much, you might be able to get away with wrapping a bunch of foil tape around the end of your pipe until you get it to the desired thickness and fit it into the muffler that way- but that's the ghetto solution and is more of a stopgap measure than a fix. You can find the tape in the HVAC aisle in your local hardware store. :-)

 

Walker 41963