Hey guys new here to the forum and I'm getting ready to put an exhuast on my 03 5.3 and was wondering if it would be better to just replace the muffler with a flowmaster or run 3" for the cat back with a flowmaster. Would I gain anything with the 3" over the 2 3/4"?

 

if you plan on just doing the basic bolt-ons like... intake, computer, etc... i would just stay with the 2 3/4, ditch the flowmaster and go with something like hooker aerochambers or magnaflows. these are more of a performance muffler. now if you plan on heavily modding the truck like... cam, stall, supercharger, turbo, etc. then go with the 3" or 2.5" true dual exaust...

 

The above is good advice.. Just try to remember this rule of thumb..

<400WHP = <3"
>400WHP = >3"