I would like to hear from anyone who has installed a Flowmaster muffler on their stock exhaust system. I am interested in whether or not it is loud in towing. If you experience any drone at 1600 to 1800 RPMs. This will be a catless system LB7. Has anyone else used a different muffler without going to a full 4 inch system?

Any input will be appreciated.

Allyn

I have an 03/CC/LB7 with no cat. I replaced the stock muff with a flo-53553 and ran the truck that way for a year, including quite a bit of towing my 7000 pound travel trailer. I did have some minor resonance from 1600-1800 and also the system was louder than stock in the 2200-2800 range, although not objectionable.

In an attempt to reduce the noise I ordered a spintech muffler that was dimensionally the same size as the flowmaster. While it is louder at the tailpipe, it is quite a bit quieter than the flowmaster inside the cab, EXCEPT that the 1600-1800 resonance was made worse (or else it just seemed worse because the system was so quiet at other RPM's). To address this I tried clamping 4 pieces of 3/4 angle iron on the front pipe as several others have done and this pretty much eliminated the resonance. The system is still louder in that RPM range but now you can actually hear the engine and tires, and don't have to turn up the stereo louder....and the wife's happier with it, too.

To do it over I would have tried the angle iron with the flowmaster, but didn't know about that trick at the time.

BTW the flowmaster was about $125 and the spintech $140, both in aluminized steel. The spintech can be made in stainless, the flowmaster is not available in ss.

I'm going to stick with the spintech until I replace the entire exhaust with a 4" aftermarket system.

Which is Louder at the street level?

Neither muffler is particularly loud, but the spintech has a deeper/throatier tone to it, certainly more attention-getting then the flowmaster which made noise but didn't seem to compliment the inherent "diesel sound" of the dmax. A couple times the spintech has surprised me, I had the windows down and either went under a concrete viaduct or passed by a retaining wall, and suddenly the truck sounds great, just not noticeable in the cab with the windows up and the radio on........

I have run the Flowmaster muffler for over a year on my 02 Duramax. There is a little difference from stock but not that much IMO. Sounds great outside of the truck and you should notice little difference inside the truck even when towing. I have had many compliments on the sound.