Submariner

I own a 2003 2500 Chevy Avalanche with the 8.1 Big Block. I recently followed some advice and ripped out the stock exhaust and put in a set of Magnaflow 12259's (3" in and Out) as a result I ended up with great sound but lost both HP and Torque. I pull a 8000K Travel trailer and can't afford the loss. Now I'm looking towards replacing the system with either a Gibson duel swept side or a Magnaflow single side catback system. Any help is greatly needed and greatly appreciated. I don't mind the sound of a loud exhaust and actually enjoy it (minus the resonance) but do not want to sacrifice the loss of the torque and HP.

BlownChevy

iTrader: (20)

I would PM Oxidizer and ask what he would suggest. He heads up the engineering side of Magnaflow.

1ImperialSS

iTrader: (5)

maybe you dont have enough back pressure for the BB

CHEVY6000VHO

iTrader: (2)

That is exactly the problem. The 8.1L needs the back pressure for that bottom end torque. You need an exhaust system that goes in one large 3" pipe, or in two, 2.5" pipes, then out one large, or out two then joining into one 3 or 3.5" pipe. You can always split it after the single out pipe, but it's better if it stays one.
Yes, the Gibson systems do offer a towing system specific. That one or one similar would be the way to go for your application of towing heavy weight.
The stock exhaust system is actually a great set-up, but I'm sure you were looking for a little exhaust note for your personal preference.

Jim

Richard@WCCH

iTrader: (3)

Just a thought, but have you checked the state of the tune after the exhaust upgrade? It's entirely possible that the system is running very lean and that really hurts low end and mid range power. You may also find that a few more degrees of timing my bring back that low speed grunt.
Other than a real loud exhaust note, I'm not sure how low back pressure without headers will hurt your low end torque.

Richard

bud8fan

iTrader: (9)

yep...sounds like you need a custom tune or someone to look at yours and see if they can help it a little....

Submariner

I retuned after the exhaust install and while that did make a difference I still lost power. I was under the impression I would gain power and torque with a duel setup. And yes I wanted the exhaust to be louder.

Submariner

Oh and one other question. It won't hurt anything to tow with this set-up will it? I am going camping next weekend and do not have the time to replaced the exhaust. I realize the torque and HP are lower but I can't imagine they are so low that it would cause an issue. The tow is only an hour away on mostly flat roads.

.T.

You're not going to hurt anything by towing. Likely you'lll find that you have better HP once you get the trailer rolling due to the increased flow.

I'm assuming that it's your SOTP meter thats got you feeling a lack of torque. As Richard said, you should look into tuning before you scrap the system.

zippy

With the increased airflow you've likely moved too far down the timing table to get a gain. Have the PCM fixed and you should be fine.