Dual exhaust warning
 

With the six speed transmission , performance exhaust doesn`t sound good at all. This transmission seems to be shifting all the time and the exhaust note is not pleasant

Re: Dual exhaust warning
 

i'm guessing what you are hearing is the afm kicking back to 4cyl. has nothing to do with the tranny shifting.

i have a dual exit magnaflow system on my 2009 cc z71 and it doesn't sound any different that what i would expect from a 5.3l.

Re: Dual exhaust warning
 

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.

Re: Dual exhaust warning
 

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.

Re: Dual exhaust warning
 

You still need back pressure for your engine to properly scavenge. And yes, the stock single exit is 2.5 inch. Entering the muffler is 2.75 I believe. So, if you install dual muffler with 2.5 inch pipe, you will have over-scavenging. Over-scavenging waste fuel. Been proven on many other forums with the 07+.

I average a mile to the gallon better in my truck compared to my buddy with the same truck only 3 years newer. We have the same CAI, both have single in dual out. His is 2.5in and mine 2.25in piping. He has a chip and throttle body spacer. Before his upgrades, we averaged the same fuel economy. After his exhaust he averaged 14mpg, down from his original 16mpg. Which is where I am at with my upgrades. He averages between 15 and 15.5 now.

Ultimately, I wanted to make my truck a bit louder and be heard when I get into the throttle. Not like my previous 2.5in system which was too loud after a bit and I experience the loss of fuel economy. From the research and talking to my exhaust guy, I found out why. I also have plenty to learn, and may not be completely right. This is just from my experience and comparison between two of the same trucks, and research.

Re: Dual exhaust warning
 

there is no way 2.5" tail pipes are over scavenging. the manifolds and cats are not efficient enough for that to happen. i average 16.4mpg hand calculated, with no tuner or CAI. you would need some serious exhaust for it to over scavenge, and a camshaft with a lot of overlap, which the stocker does not have.

you forgot the driver mod, 2 identical vehicles with different drivers will execute different results. you friend is enjoying the sound and extra power more than you are, that's easy to see.

Re: Dual exhaust warning
 

I installed a set of Kooks headers, 'Y' pipe and then a Magnaflow muffler with dual exhausts out to the rear on my 2011 GMC, with a 5.3 and a six speed auto. Yes the sound is different in the 4 cylinder mode and it does seem to drone a little. WIth my tune, we deleted the AFM adn now I run in 8 cylinder mode all of thetime. I just drove a 2000 mile round trip and averaged 20.5 MPG while running at the highway speeds along with traffic. I cannot complain.

Re: Dual exhaust warning
 

Frank, where did you get your tune? I'm trying to decide who to go with when I put my headers on.

Re: Dual exhaust warning
 

The person that I am using is Anthony Dreiling from Topeka, Kansas. He works at Forbes Field during the week and does this stuff on the side. He is ex-Air Force and has a large background with computer electronics. He goes by AkNovaMan on the web.

Anthony Dreiling
aknovaman@Gmail.com

785-608-1342

Re: Dual exhaust warning
 

I sorta like the sound i get out of my 6.0 with the fatty exhaust pipes, a little bit of throaty, and real nice when you pull that beast out to pass.

plus i'm not sure i can duplicate what i have on my 82 and go with old dual glasspacks sans converter.