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      09-09-2011, 06:03 PM   #1
HP Man
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Smile Different Modified OEM Exhaust Inspired by Subw00er

I think many of you are aware of the awesome Bates Prototype Valvetronic Exhaust Subw00er created. If you are not, then it is definitely worth your time to check out his thread http://www.m3post.com/forums/showthread.php?t=253661

I admired his work at the time and liked the idea of exhaust valves as I sometimes want a loud exhaust and sometimes like some stealth. At the time, Kreissieg was the only valve-based exhaust on the market and it came at a rediculous price. As such, I settled a couple years ago for installing electronic cutouts in the connecting pipes. While this provided the adjustable exhaust volume I desired, it also produced a mighty drone, which ultimately was not acceptable to me. Consequently, I searched for a different solution.

I decided to take Subw00er's design and modify it slightly. I realized that there was enough room immediately behind the stock muffler and in front of the rear bumper to locate the exhaust valves rather than on the side / corner of the muffler like Subw00er did. As such, I dug out the grinder and welder and began my work.

The picture below shows both the stock muffler design and how I modified it. The left side shows how it is stock and the right side shows how I modified it (sorry for the crappy diagram). Essentially, I cut into the exhaust tubing immediately after it leaves the Helmholtz chamber and connected it to the inside exhaust tip. I also modified the exhaust tubing that exists the absorbtion chamber such that it only connects to the outside exhaust tip. The result is that when the valves are closed, the exhaust will flow through the Helmholtz chambers, through the absorbtion chambers and out of the muffler via the outside exhaust tips just as stock. However, when the valves are open, then exhaust will still flow through the Helmholz chambers but will be released out of the muffler via the inside exhaust tips before it enters the absorbtion chambers.

The end result is similar to Subw00er, being lots of volume but no drone when the valves are open, and almost OEM souding with the valves closed. The difference from Subw00er's setup is that the valves are essentially hidden by the rear bumper -- if you look carefully through the black hexagonal mesh in the bumper, you can see the valves.

I will try to post some pictures later and get some sound clips as well, however, I must warn you that my welding skills are challenged and the stainless double walled is a bitch to weld IMHO, so it is definitely not as pretty as Subw00er's. The saving grace is that I painted the whole muffler flat black before installing it, so the ugly welds are mostly hidden.

All in all, I am very happy with the setup.
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      09-09-2011, 06:34 PM   #2
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Cool idea!
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      09-09-2011, 11:54 PM   #3
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Here's a couple photos of the internal plumbing and my fabrication in progress and after completed and installed on my car (sorry, but the tips are very dirty).
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Last edited by HP Man; 09-10-2011 at 04:03 PM.
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      09-12-2011, 08:35 PM   #4
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That looks really good... Seems like a lot of work though.
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      09-13-2011, 12:01 PM   #5
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Thanks -- it definitely is a lot of work and not for somebody who doesn't enjoy this type of tinkering. I'm going to try to find time in the next few days to record some sound clips, as it appears to be deceivingly quite inside the car yet very aggressive outside when the valves are open, which is exactly what I wanted.
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