This post will likely not be of interest to most people, since it seems folks are interested in a 'beefier' exhaust sound - louder than stock, not quieter. However, for those who want performance without the loudness or noise, please read on.

Originally I put the Radix on and was going to leave everything else alone. In the process troubleshooting a low power condition (which would turn out to be a bad Radix install), I was told by a number of people that my stock exhaust system was holding me back. Reluctantly, I decided to get an aftermarket cat back.

My first cat back was a Gibson single-in, single-out, side-swept. I couldn't get that piece of crap off my truck fast enough - it had horrible noise, and a endless drone between 1600-2200 RPM's (which was, of course, where I always drove). The shop that installed it agreed it was garbage. They felt really bad and refunded my money.

After some research and talking with an exhaust shop owner, I was sold on the Flowmaster Big Block 70 Series muffler (P/N 530722), single 3" in, dual 2.25" out. I was told that it was almost as quiet as stock, and that it had a low rumble, no resonance. Once it was installed I agreed. It wasn't as quiet as stock, but it was better than the Gibson, so I kept it on. I would have liked quieter, but oh well.

Then one day I saw the inside guts of a Flowmaster. Wow. All kinds of impediments to flow ('flow-master'? I think not - maybe 'baffle-master')...

Typical Flowmaster internals:



I could see how that would be holding me back power-wise. So back to the drawing board....I began looking at exhausts again. Long story short - I arrived at my ideal solution. My Avalanche is 18.5 feet long, so I have lots of room for exhaust. I decided to fit as much muffler under there as possible....but it would have to be of the straight-through variety, so I decided on two Magnaflows.

MUFFLER #1:



MUFFLER #2:




Here is the inside of the 12588/14588, considerably different than the Flowmaster:



I removed the Flowmaster and welded the two Magnaflows in series, one in front of the other, utilizing the existing dual 2.25" side tailpipes I had previously been using with the Flowmaster. The result is an exhaust system that is quieter than stock, yet has no restrictions to performance, as both mufflers are straight through. Not only is there no resonance, there is literally no exhaust noise whatsoever - zero. Yet, I anticipate gains, both on the dyno and at the track. I couldn't be happier.

What is interesting is that despite how quiet the Flowmaster Big Block muffler was, with the Magnaflows I can now hear all kinds of things that I couldn't hear before, like wind noise, tire noise, and everything about my motor and the Radix. This has convinced me that the next mod should be soundproofing.

 

very nice choice. i feel that these newer type mufflers with the true straight through design are certainly the way to go. flowmaster was the hot ticket for many years when they came out since they outflowed your average turbo muffler by a longshot. in this day and age, flowmaster hasn't went back to the drawing board for anything other than to get rid of the signiture..."Flowmaster, the resonance maker". with a different goal in mind i might not have went with 3 mufflers due to weight, but it's good that you now have a very quiet and yet near zero restriction exhaust. well done Av.

 

Well, considering The Beast tips the scales at 6,000+ lbs with me in it, I wasn't worried too much about another 15 or so lbs.

 

lol, i know what you mean. i'm just a fanatic about weight. i rarely drive with more than a half tank of fuel and never put more in until the low fuel light has come on or the tank is on E. I only fill up when i'm doing mpg testing or going on a long trip... anywhere i can save a few pounds i do. i've even went as far as to run less coolant and washer fluid in one of my vehicles.

 

the "muffman setup"? i figure you would know what im referring to since your an avalanche guy. am i right?

glad you got it how you like it.

 

I my last muffler was a single chamber flowmaster and it was louder and and had more resonance than an than my open cutout,go figure? I get sick of having a loud truck when driving for more than 15 minutes so I bought a big magnaflow 22x8x11. with my cutout closed the truck is stock quiet. all I can hear now is my valvesprings and that other anooying squeeking noise that I can't find!

 

Yes, you are correct. That is his 'pet' setup. In spite of how much I told him I wanted both quiet and performance, he recommended the FM70 over the Magnaflow. Much later, he admitted that the Magnaflow 12588 was quieter, but told me that he recommended the Flowmaster because the 'quality' of the sound was better than the Magnaflow.

This Magnaflow x 2 setup is what I should have had from the get-go. I'm very, very happy.

 

I bet that is quiet
if I understand right thats like a 40" muffler

cool setup

can you really hear the radix now?

 

As a matter of fact, yes - the Radix, the A/C, my 918 springs, little plastic squeaks, etc....

 

Nice exhaust.

And no drone.

It will be interesting to see how the Radix likes it on the Dyno.