I just installed a magnaflow cat-back on my 2000 ECSB last tuesday. I like the sound a lot, not too loud, but a nice rumble when you get on it. The muffler is polished stainless and it has the mandrel bent tube (single) coming back to a polished tip. I am however very suprised and disappointed in the fact that my E.T did not pick up at all. Nothing, NADA, zip, zero! My truck averages (ten run average) 15.53 before the exhaust, and I made three passes on friday night of which the best pass was a 15.55. Was I expecting too much. Even a 15.4anything would have at least made me feel better. According to the majority of people on the post I chose the Magnaflow over the rest, and I think I may have made a mistake. Oh well, you live, and you learn. I guess my next step is a custom true dual from a local muffler shop.

 

I spoke with Magnaflow about thier catback last year, and they reported only a 7 hp gain over stock with the 5.3. There were more than double the gains on a 6.0 in a HD.I think most people like the magna flow because it has a nice sound with no cab resonance.

 

what kind of gains were you expecting...JUST changing the exhaust will hardly ever net any kind of gains on the track...i went from stock manifolds with cats and dual flowmaster 2 chambers to headers, no cats, and true dual with 1 chamber flows and had no more than a tenth of a second change in ET. the headers were shortys though...but still i changed the ENTIRE exhaust system and had minimal gains. nothing a 125 shot couldn't fix though.

 

Well I just took off a Magnaflow muffler, it's their large case one. It was a single 3" in and dual 2.50" out but I ran 2.25" pipes so I wouldn't loose low end. Anyway, I wanted a quiet exhaust so I put on an 03 Avalanche muffler and tailpipe, it's a 3" mandrel bent tailpipe. I've lost zero performance with it, only lost the noise. I'm always playing with my truck, HPP setttings, air fliters, etc. My 0-60 time with the Mangaflow and NO HPP tuning was in the 6.1-6.3 range depending on how much tire spin I get. With the HPP 93 tuning the 0-60 time dropped to the 5.90-6.1 range. I tested both since putting on the Avalanche muffler and my time didn't change at all, zippo. My muffler guy told me that the OEM exhausts are better than people think they are, most of the time you're just adding the sound.
Jim