Tail pipe halfsies?

[-=Jeff=-]

Originally Posted by WARP TEN

Hi Bill- This has been discussed over the years and relates to the construction of the muffler to reduce resonance. There should be several threads related to resonance that discuss this. One exhaust pipe goes into each muffler and two tailpipes come out, but only one actually flows exhaust straight out; the other is mostly cosmetic. If you cut one of your mufflers in half horizontally you would find that the rear two thirds of each muffler is a closed chamber with a 1 " or so diameter tube going into it. (Sometimes there is a small 1/2" dia. tube that goes through the chamber but doesn't connect with it to flow just a little bit a exhaust. Not sure why other than a bit more pressure relief).

The chamber is called a Helmholtz resonator and it engineered to be a specific shape and volume to cancel out one of the two main natural frequencies that our engines generate that create the intense resonance or "droning" under light to moderate load at 1800 and 3400 rpms that you have heard many with certain aftermarket exhaust systems complain about. The exact shape and size allow for sound waves of a specific frequency to enter the chamber, bounce around and cancel each other out. The center resonator also has such a Helmholtz resonator for the 3400 rpm frequency of 230 Hz; the mufflers deal with the 1800 rpm one of 120 Hz.

Sometime people drill out the dummy tailpipe thinking they will get better performance and a better sound. They are rewarded with the same performance and a loud droning at 1800 rpm. Bad idea. Corsa also uses Helmholtz resonators, and I suspect some newer ones of other makes now do too. Most of my research on this was done in the 90s; I am sure that several manufacturers hove found solutions to this problem. At the time, only the stock and Corsa systems tamed the resonance. Hope that helps--Bob

Sorry to bring up an older thread, but I had a question for you Bob (WARP TEN). I know you have done more research on exhaust system than any of us. So would location of the resonator effect anything? meaning what if it was moved back to allow a pair of cats at the beginning of the tunnel? specifically with an OEM exhaust, for conversation sake.. 1990/91 exhaust, 93- newer resonator/ C6 Z06 Cats, I know the cats will fit side by side in the tunnel, I have done the bullets in the tunnel on another C4

Just thinking 'out loud'

[WARP TEN]

Originally Posted by -=Jeff=-

Sorry to bring up an older thread, but I had a question for you Bob (WARP TEN). I know you have done more research on exhaust system than any of us. So would location of the resonator effect anything? meaning what if it was moved back to allow a pair of cats at the beginning of the tunnel? specifically with an OEM exhaust, for conversation sake.. 1990/91 exhaust, 93- newer resonator/ C6 Z06 Cats, I know the cats will fit side by side in the tunnel, I have done the bullets in the tunnel on another C4

Just thinking 'out loud'

Hi Jeff--
Never a problem to bring up an old thread. I think it is great to occasionally review some of the info we have gleaned from our ownership of ZR-1s over the years. As to where you position the resonator, I don't believe that it matters at all where in the system it is located; it attenuates the offending frequencies no mater where it is. In fact, the only items that are location sensitive are the catalytic converters, as they need to get very hot to function properly so they need to be as close as possible to the fire in the cylinders.

The only other exhaust system component location discussion I have had has come up about cutouts. Marc and I have a little debate about where to locate cutouts on an exhaust system, with him favoring a straight shot right before the pipes bend in front of the tire carrier, thereby eliminating the spare and carrier. (The picture on his web page shows this location). I favor the Tony Davila approach of right in front of the rear mufflers, coming off at a right angle, to preserve the spare tire and carrier. (Pictures of mine in my albums section). I think we both agree that once the exhaust gets back to the mufflers, with cutouts open (even at 90 degrees) plus the mufflers flowing any remaining exhaust that doesn't go out the cutouts, there is little performance difference between the two locations. --Bob

[-=Jeff=-]

So Bob,

on your old 95.. you had Stock exhaust with cutouts.. By that I assume not headers correct?

[WARP TEN]

Originally Posted by -=Jeff=-

So Bob,

on your old 95.. you had Stock exhaust with cutouts.. By that I assume not headers correct?

No Jeff, I had SW headers and no cats after Marc did the 510 package. But a stock "Cat Back" exhaust that I then had Marc modify to have the cutouts in front of the mufflers. You can see it pretty well on some of the pics in my albums section. I still have the original cast iron manifolds and cats though.--Bob

[-=Jeff=-]

One more for you Bob

you had Corsa and you had the Headers/OEM setup.. which did you like more and why?

[WARP TEN]

Originally Posted by -=Jeff=-

One more for you Bob

you had Corsa and you had the Headers/OEM setup.. which did you like more and why?

HI Jeff--
Over the years I tested about six different aftermarket exhausts and based on sound, lack of resonance and performance I went with Corsa for most of those years right up until I went back to the stock cat back exhaust with cutouts. On the 93 we had headers with cats mostly plus the Corsa, and on the 95 headers and no cats with Corsa and Stock. My conclusion is that with a high flow aftermarket exhaust system, the catalytic converters soften the sound and make it a more pleasant driving experience. I always said it seemed to be about a 20% improvement in the sound, whatever that means . I believe they only cost about 2-4 HP and do make the exhaust smell better and help the environment. With no cats there was definitely a noticeable smell on startup, kind of like we used to get in the 60s and 70s. But not so bad that I wanted to return to having cats in the system on the 95. But it was quite loud with the Headers, no cats and the Corsa, an issue resolved with the stock systems and cutouts. When I was younger I think I liked the Corsa with cats the best, but as I ease into old age, I really liked the stock system with cutouts. Quiet when I wanted it (but still a decent sound), a nice rumble with the cutouts partly open, and a straight thru exhaust with them fully open for racing and scaring dogs and small children. But as they say, your mileage may vary.--Bob

[-=Jeff=-]

Cool, Thanks for your input..

I currently run Headers, Cats and Corss. my biggest complaint the the popping of the Corsa.. I have a different set of Cats and access to my stock exhaust, so was thinking upgrade the esonator which I think I have a 93 one in my attic along with the different cats and leaving my headers on..

All just thoughts at the moment..