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MBellRacing's Avatar
Join Date: Jun 2017
Location: San Mateo, CA
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Dynomax 17676 Muffler Install

I recently installed a Dynomax 17676 muffler, and have to say, it is very well suited to the Porsche 911. While it is noisy, and does seem to emphasize the poorly designed, unequal-length exhaust system on the catted 3.2, it sounds very raspy and aggressive. It also fits very snuggly inside the bumper cavity and is easily half the size of the factory sausage.

Installation involved welding and cutting, obviously, but wasn't difficult. It seems the 2.5" ID of the Dynomax muffler is a hair under 2.5", and this made it difficult to fit my choice Vibrant exhaust pipe. To fix this, I found some poorly tolleranced Pep-Boys exhaust tubing reducers which fit nicely inside the muffler. Unfortunately, this metal is very bad, and this made welding very difficult. Should I ever need to do it again, I will likely just cut relief slots in the muffler's inlet and outlet pipes to better fit the Vibrant (or similar) exhaust pipe.

There is no outlet/inlet on the 17676, at least I don't think there is. Either end can be used as an inlet. It seems very symmetrical internally. Fitment involved, for me, a quick 6mm hole drilled in the stock muffler's clamp bracket thing in the heater tube and a tab welded to the muffler. While many will claim I've "ruined" something irreplaceable, I feel it was a necessary sacrifice, as it allows for a very secure mounting position that holds my muffler against gravity very effectively.

I found the standard, Pep-Boys-supplied Vibrant 2.5" 3-bolt exhaust flange to be nearly-exactly the 2.9" required bolt spacing. It fit nicely, but does require some fine tuning when tightening the bolts from the cat bypass to the muffler. It wouldn't take much to severely misalign the tubing.

All that said, without the beer breaks and the time spent measuring, cutting, and welding away from the car (no extension on the welder to weld on the lift), I'd say it took me about 3 hours of work, minus the flat black paint.

My mistakes: I definitely didn't cut very effectively. The tailpipe, specifically, was not cut tangentially and has an edginess to it that could be avoided. While I'm sure the muffler offers much more restriction than this mistake, it bugs me to look at it. I also cut the tailpipe a bit too short, and it heats up my bumper. I'll add a tip later. Finally, I didn't take into consideration the stretching from welding, and all my nice measurements went out the window as I was assembling. I had to call a couple audibles to make up the difference, and as a result, the muffler sits dangerously close to the inside of the bumper. As mentioned, avoid use of poor-quality exhaust components like the Pep-Boys reducers. The don't weld like the rest of the exhaust components and are difficult to deal with. I made a few holes and had to fill with some bird poopoo welds. Oh well, only I know they're there!

It is hard to say exactly how loud the system is. A friend who helped me hold things in place for installation has a 2016 Mustang GT with an MBRP cat-back and stock cats. While revving in a parking lot, his exhaust is still slightly louder than my cat-less Dynomax 17676 system, for reference. I would say full throttle, full load, my car is probably a bit louder than his, thanks to a catalytic converter missing.

Here is a photo of my completed muffler and a stationary video (all the way at the bottom of post) at the shop. Enjoy.

Last edited by MBellRacing; 06-27-2017 at 10:16 PM..
Old 06-27-2017, 10:13 PM
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Chain fence eating turbo
Join Date: Dec 2008
Location: Austin, TX
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I love it! I've been wanting to a 1-chamber Flowmaster on my turbo'd 3.2, so happy to see other's experimenting and their results as yours.

I wouldn't sweat the tailpipe, I didn't even notice until you pointed it out, and even then....

Sounds pretty good.

My favorite I've heard is the M&K muffler. It's perfect.
Cory - turbo'd '87 C3.2 Guards/Blk, 3.4, 7.5:1 CR P & C's, soon to be 993SS cams and GSXR 750 ITB's fed by 964 intake, Borg-Warner S366 turbo @ 1.4 bar, Treadstone full bay IC, TiAL F46 WG, HKS 1 1/2" BOV, twin 044 pumps, MegaSquirt 2 (v3.57 board) w/EDIS, Tramont wheels (285's rr, 225's frt), Big Reds frt, 993 rr., tower brace, MOMO wheel
Old 06-28-2017, 04:22 AM
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Looks nice to me! Which grade wire did you weld with, please?
Old 06-28-2017, 09:10 AM
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Thanks, guys! I'm not sure on the grade of wire. It's been in the MIG for about a year now at my dad's shop. It's probably reasonably good stuff. My big issue with the welding, as mentioned, is that the Pep-Boys reducers took a lot of heat and low feed, the muffler liked low heat, more feed. Finding a happy setting and moving appropriately fast was difficult.

I'm out racing the next couple weeks, but once I'm back, I'll make sure to take some video of the car driving and maybe even a dB test from 50' compared to a few other cars. It sounds way louder with he window down while driving than it seems standing right behind he car, which is weird! Overall, very happy with it!
Old 06-28-2017, 09:39 AM
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KTL KTL is offline
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Yep the 17676 muffler is a universal muffler and has no direction of flow. The inlet/outlet location you choose doesn't matter.

I had this muffler on my '87 with a Fabspeed cat bypass/premuffler and I really liked how it sounded. A bit grumbly at low rpms but not unruly at all. At high rpms it rips nicely. Here it is on a friend's car
Kevin L
'79 911SC widebody conversion
'86 Carrera
Past: '87 Carrera "The Unicorn"
Old 06-28-2017, 09:51 AM
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Ah OK, I thought the muffler was stainless and wondered if you used stainless welding wire also - I now see that it is aluminized steel.
Old 06-28-2017, 11:16 AM
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