==> audio in subsequent reply


What did it replace?
The stock system on this car was mostly gone when I purchased it. The only OEM parts left were the GT resonators. The catalytic converter was replaced with a pair of 2” straight pipes with a 1” H connector for the 02 sensor. This small diameter H was not effective in mixing the pulses and only provided a collection area for the 02 sensor. These pipes were connected to the GT resonators via a 1.75” reduction pipe. Out of the resonators was a 1.75” Y pipe merging into a single 2” pipe and into a single inlet muffler of unknown manufacturer. This system was fairly loud, it sounded pretty good but had a very American V8 burble of a mid 70’s Camaro. Here are some pictures of the original system. I don’t think there was anything very redeeming about this system.



Here is an overview of the exhaust system recently installed in my 928 S4 5spd. It’s using the following components:

• X-Pipe: Motorsports Inc. 2.5” Stainless
• Center Resonators: Magnaflow 2.5” dual inlet / 2.5” dual outlet (PN 11376)
• Rear muffler: Magnaflow 2.5” dual inlet / 3” outlet (PN 12198)
• Exhaust Tip: Mangnaflow 3” inlet oval exhaust tip (35171)
• Tubing: 2.5” stainless TIG welded

This is the Motorsports Inc X-Pipe. It's a pretty nice piece. It is mandrel bent and sectioned together. I will point out that the MIG welds were a little messy and needed to be cleaned up on the inside. Additionally the flanges needed to be sanded smooth. But other than that, the fitment was perfect.



These are the collars used to join the X-pipe to the rest of the system.



Mandrel vs. Crush Bends
I would have preferred to have a seamless fully mandrel bent system. The assumption here is that is it constant diameter with no seem disruptions for better flow. At least that is the theory, I am not sure how effective that would be at the 2.5" diameter on this 5.0L motor and not sure if the efficacy is required further downstream as exhaust gases cool and become less dense. Anyway, I could only find one vendor within a 100mile radius to of Portland that offered mandrel bending. They seemed capable of doing the work, however, they had a very long waiting list and I tried to get an appointment for several months without luck.

In the end I found a custom fabricator, Skill Set Fabrication, who does a lot of custom fabrication for my work here at Nike, as well as a bunch of hot-rods. He has a reputation for detail AND he used to own/maintain an couple 928's so that gave me some comfort. We discussed options and felt the best approach would be to use a combination of crush bend and mandrel pre-bent sections with the objective being minimize bends and bend radiuses, and minimizing seams. All welds are TIG.

The OEM hangers were salvaged from the GT resonators and used to hang the new resonators.







Here you can see a mix of Mandrel sections and crush bend sections.




The exhaust tip stick out a little more than I would like. It had a long neck, which we trimmed a few inches off, but if we go shorter, I would need a custom tip and that would be single wall. We looked at moving the final muffler more forward, but that would require sharper bends and pipes would get a lot closer to the suspension.

 

Oooooooooo...

 

How does it sound?

You can have a listen for yourself. I made this recording with my iPhone and so the speaker cutout for a bit during startup. Also, both of these recordings were done with the exhaust cold. I notice the tone gets a little deeper as the system warms.

Across the entire range it is about 25-35% quieter than the previous system. Those GT resonators must be hollow because they don't seem to contribute to any muffling.

At RPM’s below 3500 it is subtle, above 3500rpm it gets much louder, it sounds very Eruo and tight. Most of the sound out the exhaust is the sound of the motor, no funky resonance or artificial sounds. It sounds very similar to the Gregg Brown systems that are used on the stoker 6L motors.

The sound quality if much more balanced. The car no longer has that uneven burble of the V8. I would attribute that to the X-pipe blending the pulses.

 

I LIKE.

 

I have almost the identical 3-muffler setup with an X; my mufflers are a little longer. Love the sound, zero droning.

Looks and sounds good, nice job!

 

Agreed, no drone at all. It sounds "engineered" I guess we got lucky ;-) Although my understanding is that uneven length tubing can address any drone issues, as well as using straight trough mufflers.

 

Very quiet, you can hear the engine rev more than the exhaust. Would be interesting to compare it to the stock setup

 

I'll try and get some recordings outside of the garage, which I think is a bit of an echo chamber and that is over powering the exhaust note.

I forgot to mention, the performance improvements are significant. The car is noticeably faster in accelerating and revs re much freer.

 

Very nice job, and I love the sound

 

I did a very similar system , same magaflow mufflers + headers and had terrible droning
changed the mufflers to dynamax with the flappy and the drone is gone
picked up 31 HP at the rear wheels

 

Nice job. It makes sense that the x-pipe, three mufflers, and the rear muffler (re)combining the sides fully after unequal pipe lengths gives more of sports car sound, instead of the American muscle car V8 sound.

 

Now that is how a Euro V8 should sound. Thank goodness it doesn't sound like an old pushrod V8