So many of the aftermarket exhaust systems (catbacks) have been reported to suffer from an annoying droning or booming resonance at low rpms that it makes me wonder what design feature they all share that is the root cause of the phenomenon. Note that not all systems have this behavior, so it cannot be anything fundamental to the Cayman.

Some systems that have been reported to have this problem include Miltek, Tubi, AWE, Remus and Fabspeed, among others.

Systems that do not have this problem include OEM and Capristo (there may be others).

One feature that many of the booming exhausts share is a large, unbroken, sometimes completely flat surface on the muffler. Niether the OEM or the Capristo exhaust have this design feature - they both use frequent "panel breakers" to provide some out-of-plane stiffness to the surfaces of their mufflers.

I wonder if perhaps the outer surfaces of the mufflers might be undergoing a "plate bending" resonance that produces the booming drone. This would not occur on the systems that use panel breaks to stiffen-up the muffler cans.

Do we have a list of systems that absolutely do not drone, and do each of these systems stiffen the muffler surfaces with panel breaks?

I would actually say that my AWE has the same resonance that my stock did between 2500 and 3000. The difference is that it is louder, as the exhaust is louder.

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Milltek has no drone at low rpm. It is as quiet as stock. I have milltek now and I want an exhaust that is a little louder. I was thinking of taking out the smaller silencer mufflers. If you want a quiet exhaust I would add milltek to your list as well.

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Does anyone know of a exhaust maker beside B & B who has O2 sensors iwith cats behind the header section? I have the full B & B header exhaust set up and would consider going with a quieter exhaust, but need to find one with that option. Besides stock of course.

Capristo has that aS a special order option.

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K-Man S

Thanks Ken.

Ken, who would I contact to inquire on that? Went to their website from the sponsor page. Mostly in German (even when I press "English").

Thanks again,

Brian

From the feedback we've gotten on the Miltek exhaust, it seems to be very polite, with no cabin resonance. It definitely has a different (IMO better) tone than the OEM, but like porsches4ed said, it's really not too much louder than stock.

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I have owned tubi and milltek systems. Milltek is quiet as a mouse. At a track day noise test I frequently got the lowest reading of all all the cars.....no resonance either. The tubi was horrendous. I mean its so loud you need ear protection - the added resonance when wearing a helmet was skull splitting. It sounded fantastic on full bore but between 2,500 and 3,500 rpm you need a brain surgeon on standby. Milltek cat-back is great on all accounts although I would argue that its quiter than stock - its like a mouse wearing cotton socks.

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I think resonance is the rule rather than the exception. It takes special engineering to get a great sound but no resonance.

I just wish Corsa sold units for us. My L98 vette exhaust from them was $700 and sounded unbelievable yet had zero drone at any rev. No one could ask for more. It's irritating that the same thing (sometimes with drone) goes for $4000 on a Cayman.

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Does anyone have an idea where the Borla catback will fall in this spectrum of loudness/quietness? I don't have any experience with them but really like the look of their setup.