I was looking at the underside of my '03 S2000 and saw an extension that comes out of the exhaust pipe about half way down the car. It comes out of the exhaust pipe at a right angle, goes several inches and then looks like it just ends. What is this for?

 

That's a resonator chamber. It's part of what makes a "tuned" exhaust.

 

So it just adjusts the exhaust sound? Does it make it louder, quieter, or just change the frequency?

 

It also makes a good handle when you are yanking that puppy out of there to make room for your new exhaust!

 

Do a Google search on Helmholtz Resonance.

 

More specifically, it's a Helmholtz resonator. Here, it's used as a type of band-stop filter (ie, it filters out a certain band of frequencies.) That's why aftermarket exhausts which do not have this pipe have boominess at certain RPMs. The filter has an added bonus of not actually impeding the airflow in any way.

 

I learn something new every day about my S2000....

 

Elistan,

Thanks for your simple, yet complete, explanation. This car is truly an engineering marvel.

 

Don't all of the less obtrusive sounding aftermarket exhaust systems have these?

 

The only aftermarket exhaust with one of these that I know of is the dual outlet titanium Amuse one. But, it's possible others do too.