[WARP TEN]

Originally Posted by billschroeder5842

So I'm finding all sorts of do-dads on my ZR1.

I noticed that my factory exhaust only has the outside tail pipe that "works" and the inside seems to be decorative?

Is that right?

Anyone do anything different other than swap out the system?

Thanks!

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