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Problem with Fabspeed Mufflers

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Hi everyone,

I have just installed Fabspeed mufflers on my MY'99 C4.

The installation went well (aside from some VERY rusty nuts on both the muffler brackets and the sleeves that attach the muflers to the catalysts - the UK's rather inclement weather not helping here!!). The mufflers clear the heatshields on both sides of the car (at their closest point by the rear lower corner of the muffler) by about a quarter inch or so and the tips clear the rear apron correctly. There is no contact between the mufflers and the car's bodywork. All the joints are gas-tight - if I block off the tailpipes with a hand with the car cold and idling there are no leaks as the pressure builds.

The -ve battery terminal was removed after the install to reset the OBD-II and I have run the car approx 100 miles since including some hard acceleration runs (up to 155 mph - bad boy) to allow the electronics to re-map correctly. At full throttle and over 5000rpm the souind is absolutely amazing (if frighteningly loud)!

The problems I have are these:

1) Each side sounds different and varies differently with different rpms and throttle openings - WEIRD!

2) There is a massively loud boom throughout the car at 2000 - 3000rpm even at very small throttle openings. Very very loud and unpleasant.

I've had the OBD-II checked on my mate's PST-2 (He used to work for an official Porsche Center and is now an independent Porsche Specialist) and no fault codes were logged so I have to assume the variocams and other systems that might immediately account for the odd symptoms are working correctly.

Does anyone have any idea what might be causing the problems?

Hope you can help

Thanks, Ian W

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I put Fabspeeds on my '00 Carrera. Loved the sound. Did not experience a different sound coming from each muffler. It may be the muffler or it may be the catalytic converter changing the sound. Wouldn't worry too much about it. The "boom you are hearing at 2-3,000 rpms is resonance. Fabspeeds are famous for it and I had it on mine. Just a matter of acclimating to the sound.

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Thanks for the reply ncbob

Was there anything you could do to lessen the amount of the resonance? Adjusting the mufflers for instance? The resonance is so severe that I can't see through the rear view mirror at some engine speeds. If they are going to stay sounding like they are then off the car they come!!!

Think I'll be taking Mr Fabiani up on his 'no resonance - guaranteed' money-back pledge!!

Ian W

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I have fabspeeds on my 02 Cab and while there is some resonance at about 2800 rpms on mine, it is nowhere close to what you describe. I'd contact Joe F. at www.fabspeed.com

I found him to be a very fair person to deal with. Have had his mufflers on my 90 Cab; 94 Speedster; 98 993S and my 02 Cab and not experienced what you have.

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If you are uncomfortable with the sound, like Don suggested, call Joe Fabiani. He's a good guy and will listen to your problem. I never had anything like what you describe. I really enjoyed my Fabspeeds. When I got rid of the car, I sold them to a good friend and he likes them as well.

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  • 9 months later...

This is a copy of an email that I sent to Joe at Fabspeed and his reply.


I recently installed your Fabspeed mufflers on my 1999 Porsche 996 C2 with a manual transmission. Before I installed the Fabspeed mufflers I installed your Cold Air Upgrade. The Cold Air Upgrade increased the intake noise just a little bit in the higher RPM range. I was more impressed with the quicker throttle response due to the lower restrictions.

The great news is that when I added your mufflers I was very impressed with the quality of the sound and quite happy with the results. Thank you for making an aftermarket muffler that I can easily live with and enjoy on a daily basis. It's the only aftermarket exhaust muffler that I've tried that has a throaty sound at low RPMs and actually gets less rumble at higher RPMs. It "smoothes" out as the revs climb. My crossover point is around 2800 RPM. The exhaust sound does not resonate as you promised and the highway cruising sound level is the same as stock. Well at least not more noise than the tires, engine and wind generates. The only thing I noticed is around 2400 to 2600 RPMs the noise kind of oscillates or rolls around in the cabin, but only a little. As an experiment I may try putting the intake accumulator back in the intake box. You call it a muffler on your website.

I had the mufflers installed at Gossett Motor Cars in Memphis Tennessee. I had them fix a minor cam sensor cover oil leak at the same time. Wow, dealer labor rates are expensive. The dealer's service advisor and mechanics where also impressed with your exhaust mufflers.

Feel free to share this information with anybody who is concern about your mufflers being too load, like I was.

Now that I have the engine breathing better will the Porsche fuel injection system adjust the air/fuel mixture for the extra flow? Does Porsche use a speed-density system (RPM and Manifold Air Pressure), Alpha-N system (Angle of throttle and RPM), or a mass air flow system (hot wire or vane type)? What does your add-on chip do if the fuel injection system already corrects for the additional air flow?


Mike Stiffler

Joe replied

Hi Mike

I am glad that you are happy………………….if you can let other know about Fabspeed quality and service on webforums that would be great. You cars DME will automatically learn and self adjust for the lessened backpressure and you don’t need a chip. If you would like one it would be tuned for 93 octane gasoline and the mods you have made.

Let us know and have a great weekend.


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Are the GHL or PSE people having any of the resonances? This is the first I have heard of any undesireable noises from Fabspeed, and now I am worried about buying a set....

I have a tip, which means most of the time I will not control the RPMs. The tip likes to have the RPM's around 2K, so if that's where the resonance is in a system, I would have to remove it...

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When I had the Fabspeed mufflers installed earlier this week I reused the stock Porsche exhaust tips by mistake. It's my fault because I did not specifically ask the installer to install the new tips. I then put about 100 miles on the car with the stock muffler tips and the Fabspeed mufflers.

Yesterday I installed the new Fabspeed exhaust tips myself and as hard as it may seem it changed the exhaust system for the better. It reduced the overall exhaust sound level, made the exhaust sound more mellow, and got rid of the slight resonant that I heard before. It's perfect now.

It's amazing how all of this fits together. I have experienced this change before when working on motorcycles.

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Are the GHL or PSE people having any of the resonances? This is the first I have heard of any undesireable noises from Fabspeed, and now I am worried about buying a set....

Absolutely no resonance with the PSE...that was one of the reasons I went with PSE. My service advisor warned me about the resonance problem with Fabspeed.

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