I have a Magnaflow with 2.5 inlet and outlet, I, of course, have the 2.25 inch stock piping, can I just weld this onto the piping there? Its not a large gap, and I think I should just be able to cut out the stock and weld in the magnaflow, just fill that little gap with weld...right? Let me know what you guys think!
~Chris

 

Or you can just weld in a 2.25 - 2.5 reducer before and after the muffler. Would make for a cleaner instal but cost more $$. Preformance wise it would be the same either way.

 

it would make slightly more aerodynamic sense (from the inside of the tubing) to make at least the muffler outlet a smooth transition back down to 2.25". At the front it doesn't matter as much

 

That's the way the muffler shop did my muffler. They just stick the stock 1 7/8" pipe into the 2.25" and welded the gap, then the 2.25" pipe into the 2.5" muffler and welded the gap, then they spread a piece of 2.5 to do the 2.5" to 2.5" out of the muffler.

There are no leaks and it sounds great.