Quote:
Originally Posted by GMCJOE
I heard the change in the exhaust note with my 08 gmc. It's definitely from the AFM. I am running a magnaflow, single in dual out. I had the muffler shop run 2 1/4 inch pipe off of it to keep the back pressure correct so it wouldn't affect the fuel economy. Plus I didn't want it as loud as my previous 2 1/2 inch that I have ran on my other trucks. Wanted to keep the drone/in-cab noise down on my long highway trips. Sounds great cruising or getting into the throttle.
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the 2.5" pipe wouldn't hurt your fuel economy...period....it hasn't had any adverse effect on mine and it won't on any other stock 4.8l/5.3l pickup. you're stock intermediate pipe is 2.5" from the factory, so why would you go smaller, even if it is twice pipes. most single catbacks bump the tubing size up to 3" for a reason.
the majority of people are misinformed about "back pressure". the key principle in exhaust is scavenging. as far as drone, i ran a dual 3" system on a b&m supercharged 454, and it was quiet and had no drone in the cab. aside from the blower whine it wasn't too obnoxious, it was my sleeper. i had a dual 2" system on a old pickup with glasspacks that would shake your teeth out, you could hear me coming from a mile away.
forget everything you've heard about back pressure. i've put a lot of research into exhaust systems and still have a lot to learn myself.