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Custom 3" Exhaust Project
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Muffler Selection & Catalytic Converter

The complete 3 in. custom exhaust layout Here is the complete custom 3" exhaust system laid out on the garage floor prior to installation. The Evo III header (with "Sterling" Jet Hot coating) is in the foreground. Then comes the Burns Y-Pipe with custom E3 flange. This is mated to the 3" stainless tubing. In the center of the car I chose to use a Borla muffler and at the rear of the car I chose a big Magnaflow muffler. Both mufflers are of straight through design and are 3" IN and 3" OUT. Also note that the Magnaflow muffler is an offset in / center out design (reversible) which simplifies the bends in the 3 in. tube in that area.

Why such a big rear muffler? Because I am not a big fan of loud cars. The only cars that I truly enjoy at high decibels are F1 cars. They make a sound that has to be heard to be believed. But for modified street cars I think it's somewhat obnoxious when they are loud. And it does little to promote our sport in the eyes of the public. Besides, it's possible to make a car quiet without hurting its performance. You just have to throw some volume and mass at the exhaust system. Now for a pure race car the mass part of that equation can be a problem. But otherwise it's not such a big deal.

My measurements show that the stock muffler weighs 31.0 lbs whereas the Magnaflow, which is the same size, weighs only 21.6 lbs. That's almost a 10 lb savings (30%). Furthermore, the smaller Borla muffler weighs 9.0 lbs. That's a heck of a lot lighter than the factory cat' or even a SuperSprint center resonator. Both Mufflers are constructed from 100% stainless steel and should last for a long time. Each muffler costs less than $150.

The Magnaflow muffler is:
p/n 14589 and measures 5" x 11" x 22"

The Borla muffler is an XR-1 Sportsman Oval:
p/n 40944 and measures 4.5" x 7.9" x 16"

I also wanted to be able to swap a catalytic converter into the center slot. For this I chose a big Magnaflow cat with 3" IN / 3" OUT transitions. I wanted the cat' to be as big as possible in order to maximize the amount of surface area of catalyst exposed to the exhaust flow. This theory seems to have been borne out as Jim Butterworth, who is using an identical exhaust system to mine, recently passed the CA smog check with absolute flying colors, Schrick cams and all.

The Magnaflow Catalytic converter was also less than $150, just like the mufflers. It is of 100% stainless steel construction (other than the ceramic catalyst) and has p/n 94309.

In order to facilitate swaps between the cat and the Borla center muffler I used V-Band clamps which I sourced from Burns Stainless. These clamps are not cheap at $80 each (you need two) but they work like a champ. They are all stainless and are very easy to use.

Below are some pictures related to the mufflers and catalytic converter. Hover your mouse over the photos for a description:


The Borla center muffler and the cat
A look through the inside of the Borla XR-1
Comparison of the Magnaflow muffler to the Borla XR-1
A look through the offset IN / center OUT straight-through Magnaflow muffler
The big Magnaflow muffler compared to the stock E30 M3 muffler

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