So I've exhausted youtube and the forum search and now I hope one of you can help me out here.
I went to a muffler shop today to ask about installing a Flowmaster Super 40 muffler in my 2007 5.4L, and the guy told me that I should upgrade the piping to a 3" as well. My original plan was to keep the stock pipe and replace the muffler only.
What changes in performance and sound should I expect with a 3" pipe compared to the stock 2.5"?

 

Youtube straight pipe on an f150...I know my truck is up there. I love the sound of it! 100 times better than the flowmaster! Our trucks are real quiet so I just had a straight welded in place of the OEM muffler. And no drone!

 

well it wont sound as loud with only 1 flowmaster, by putting 2 and duals you will get it loud and deep like most people like. the way your talking about is going to get you tone but it wont be loud

 

There won't be a great deal more power with 3" over 2.5". A little more at high rmp but not much, especially with a chambered muffler. Sound may be slightly deeper but that depends on the tip you put on.

 

Cost me $40 at the muffler shop to weld in a straight pipe...take a chance. You'll love it!

 

Will there be any change in mpg?

 

I'm not a huge fan of the dual exhaust look and I'm looking more towards tone than volume.

 

Probably not, especially for what the upgrade would cost. You might see .1 mpg with a 3" system over a 2.5" system, but that's largely negated by a the chambered muffler impeding velocity anyways so in your case it really doesn't matter.

 

most times upgrading to a larger pipe without matching modifications will actually cause a decrease in gas mileage and power, due to how open exhaust is and decreases velocity flow. it will however definetly change the power curve. its all about exhaust velocity. imo straight pipes could probably be the worst things to do when goin for mileage and power.

id go with the flowmaster with factory pipes, opens up the restriction just enough