yes. there is a HUGE difference. I've run both and in my opinion the Flowmasters should be limited to v8's They seem to preform well on 8 cyl engines but poorly on under powered v6's and 4cyl'ers. I am currently running a Dynomax fully welded super turbo on my new 4runner with 2.25" from the header to the muffler and then 2.5" out from the muffler. The only reason I am running 2.5" after the muffler is because I got a really good deal on the muffler and it was 2.5" in and out. On a v6 I would go 2.5" front to back and on a 4cyl I would run 2.25" front to back. Pipe size matters as much as the muffler. Too small and it is too restrictive and too big it is not restricted enough. You need some back pressure for your engine to run right. It also helps to keep it as bend free as possible and only use mandrel bends