i got a full 3'' exhaust with a 2.5'' muffler at the end. im going to be replacing the muffler with a 3'' muffler, mainly because the old muffler looks beat up. will my tune be effected.

 

if you run a wideband on the car you can see if your rich or lean after the swap and go from there

 

If you are moving more air then you need more fuel to make more power. Watch your wideband, you will probably be a little leaner now.

 

Doubt it

 

The muffler portion is not a huge restriction given it is a 2.5" N1 vs a 3" N1. There is restriction no doubt, and it will show up on the dyno. But it is not a major problem until you start really pushing the upper 3 digit HP numbers.

 

A few years back my APexi muffler had a removable silencer that restriceted the muffler flow to about 2 inch exit from a 3 inch exhaust. When I took it out there was a noticable difference in the AFR's, if you dont have first hand experience keep your 2 cents worth! It will effect the AFR's but not by much!

 

well, its at the end of the exhaust, i doubt it will make a difference. If we were talking replacing the whole DP exhaust to 3" then yes.

 

I did the same thing and there was a very small change in AFR's. Nothing worth getting a re-tune over.

 

As stated, the muffler represents a very small section of the overall exhaust system. If you were going from say 2" to 3" or something similar then you might want to re-tune but with just replacing the muffler the change in air/fuel ratios is negligible. I am assuming of course that you mean just the muffler and not any other section of the exhaust system.