What do venturis in exhaust tips do?
 

I got a Techtonics Tuning exhaust with a Borla muffler installed in my B5 and I noticed on my receipt it says the exhaust tip they put on has venturis in it. I tried to read up on the venturi effect but I'm not a science buff so I didn't understand it. Techtonics says that the venturis make the exhaust quieter. Is there any benefit to having them versus a tip without them? Any help is much appreciated. Thanks.

hmm sounds interesting. can you see that part they are talking about? the venturi pattern is supposed to control airflow (i know a tiny bit about it from paintball experience). depending on the pattern, the piece might straighten out the airflow or put a slight spin on it. either pattern might help to get the air out of the muffler as quick as possible which would prevent it from bouncing around the baffling inside and making more noise. i dont have any scientific numbers or fancy graphs but i wonder know how much of a difference it would make and you certainly wouldnt see any performance gains. it might sound quieter or 'smoother', potentially less raspy if was raspy to begin with.

*feel free to correct me if im wrong but this is my educated guess, hope it helps :)

Th venturi effect to the best of my knowledge is the tendency of a gas moving through a straight pipe to accelerate as the diameter of the pipe decreases. There is more to it than that but I don't feel like explaining the ideal gas laws (good to know for those into intake and exhaust systems though). In the case of mufflers though, the idea is to slow the gas down inside the canister so that more sound can be absorbed by the filler. The venturis might be there to speed the exit of the gas in an attempt to create less backpressure.

audi5000 is right about seeing minimal if any gains from it though.