I've heard that CC's reduce noxious gases but actually increase greenhouse gases...what we need is some
real ethanol like Brazil has instead of the corn scam

...or to drive less, which would be ideal.
As far as noise, its pretty tame under 3k RPMs and the sound is beautiful because of the boxer engine; I wouldn't want to make it quieter. I've had a number of cops follow me with the exhaust and the one who pulled me over did it for another reason without even mentioning the exhaust. I'm still surprised; the thing is huge, I can stick my arm in it down to the elbow