Guys with 8.1L's!

[04GMC8100HD]

I plan on keeping the stock exh, but add a 70 series big block II flowmaster. I want a nice rumble at idle and a high performance sound under acceleration, but don't want it so loud it sounds like a tractor. Is this the muffler for me?

 

Randy

[Pancho]

I have been happy w Magnaflow. They should have the "big block" system out by now that solves the resonance problems. This was not an option for me back in early 2002 as I added inline resonators (glass packs) behind the muffler and double dynamated the cab to quiet things down inside.

[ShortCrew]

I just installed a Magnaflow. Dual 3" in, single 4" out. I absolutely love the sound. It may be a bit quite for what you are looking for, big the overall sound is fantastic.

[N900WM]

I've been looking also.

 

On the past trucks I've owned/own we completed some rather extensive dyno testing with different mufflers on 5.4L Fords and 5.3L Chevies. I realize this isn't apples to apples as these truck have less displacement and still are supercharged but...In all cases the Magnaflow systems always came out on top in regards to low end and hi end torque. The other systems we tested, Flowmaster, Borla, and Walker/Dynomax systems all did about the same on the top end but lost a significant amount of low end torque.

 

As of right now, Magnaflow tells me that they are designing a system for the 2003 8.1L extended cab short box trucks and that it will be available soon. They have a system for the 02 long box trucks but they say the there are a number of differences on the 03 trucks. They also noted that the exhaust stystem on the 03 8.1L is pretty efficient and they want to make sure they don't put a system on the market that decreases performance.

 

I'm going to wait to see what they come up with.

[awdvkd]

Magnaflow dual in dual out, very pleased, wouldn't recommend anything else.

[bigtruck21]

N900WM,

did you happen to test the gibson system as well on the 5.3L. And were you testing the kits....single 3inch or dual 2.5inch? I'm torn between gibson and magnaflow and which one has the best power from 1500-4000.

[N900WM]

04,

Never tested the Gibson.

As for single vs. dual, it depends on wether your going to build an actual dual system or just a cat-back dual. The new Silverado exhaust is pretty efficient. We found a custom true dual with a normally aspirated engine lost too much torque on the low end. However, once supercharged the numbers change in your favor. If you build a true dual system, make sure you use a cross over!

 

I ended up with dual tails and a cat-back system because it looks sexy and because I got the best low end torque. The top end power is about the same, and the single system was the same, no real difference noted between the two.

[Black02Silverado]

I plan on keeping the stock exh, but add a 70 series big block II flowmaster. I want a nice rumble at idle and a high performance sound under acceleration, but don't want it so loud it sounds like a tractor. Is this the muffler for me?

 

Randy

I have the 70 Series II big block on my 5.3 and love it. Just the right amount of sound at idle and acceleration but nonduring cruising. Didn't feel any loss of power at all and as far as gain not much there either. Just my piece of mind that it let the engine breath better than the stock muffler.

[8100HD]

Just added the Flowmaster kit to my 8.1, must say this set-up is sweet, not too loud and barely noticeable on the highway @ 75, kit has a 50 series big-block muffler that is dual 3" in and single 3.5" out definetly working well with my TOG's. No loss of low end torque, a noticeable difference in throttle response and mid power, truck moves out better than before.

[bigtruck21]

single 3 or catback dual 2.5 tails...not true dual. From what I hear, people say in the 5.3's the single 3 has the best torque in the lowend while the dual 2.5 tails has the best topend hp.