I'm getting rid of the Gibson single-in/single-out, sideswept exhaust on my 5.3L Avalanche as the resonance between 1600-2200 rpm is unacceptable. I'm looking for a quiet performance exhaust and have narrowed it down to the Flowmaster 70 series or Dynomax Super Turbo. I will be getting the new muffler welded in at the Gibson flange pipe and getting custom-bent tailpipes.

The Flowmaster 530722 muffler is a 3-inch single-in, 2 1/4-inch dual-out.

The Dynomax 17789 muffler is a 3-inch single-in, 3-inch single-out.

Does anyone have experience with either of these two mufflers and can you offer any feedback?

 

I have the Flowmaster 70's (think it's the same one) on my '03 4.8L. The catback system I got originally came with a 50-series, which was too loud for my tastes, so I changed to 70-series. Overall I'm fairly pleased with it. At lower RPM's it sounds really cool with a deep throb, almost like a big block or a diesel railroad locomotive. At about 2000 rpm's there is a somewhat whiny resonance, which might be amplified by the canopy, but is tolerable (don't know how it compares to Gibson's, but I've heard they are bad for this). At higher RPM's, 3000+, I lose the throb and it's just a steady whine, unlike the 50's which sounded cool (but LOUD!!) all the way up to red line. Also the 70's lose a bit more power at high rpm's than the 50's but are still way better than stock. Just my experience. Hope this helps :-).

 

SuperTurbo all the way! I had one on my '99 Z71 and it was great. Good WOT sound, very subdtle at cruise RPMs. I've never liked Flowmasters since I installed one (in haste) on my F150 a while back...drone sucked and don't add too much power.

Also, I think a decent sized Magnaflow would suit you well. I can't say what size but a 5x11x22 is damn quiet!