Hey experts!
Is it imperative that I replace the exhaust pipes when I install a new muffler? I'm plannning on getting a Flowmaster installed soon. My X only has 3500 miles on it and the pipes are basicaly new. I guess I'm asking if I will lose some sort of gains if I don't get the pipes replaced along with the muffler. I've read some threads here about increasing the size of pipe diameter. Any info would be great.
Thanks in advance

There is no doubt that there are more performance gains by replacing all the pipe from the catalytic converter back. However, there is a point where you loose too much backpressure in the engine thus hindering performance. The general advice I have received from the person who has done my exhaust systems for several vehicles is that going up 0.25" - 0.5" is about all you want to do. In our case, a 2.5" exhaust system is probably the most optimal. Now, if you just change the muffler to a more free-flowing muffler, you will notice an improvement just not as much. The exhaust tone will not be as "loud" as it would be if you changed all the piping. . .and of course its much cheaper just to replace the muffler. My best advice would be if you ever decide to go to a 2.5" system purchase a 2.5" inlet/outlet Flowmaster 40 series and they can size down the inlet/outlet to fit your current system but it will give you some flexibility if you ever change. This is simply my advice/experience. . .ask around there quite a few well versed mechanics on the site.