[Nath316]

Was driving tonight behind a Audi TT 3.2 and noticed that the driver side exhaust exit had a butterfly valve in it that closed as the car pulled away and opened when standing still!

3 things

is this right ?

why does it do that?

can the exhaust rear end from a TT be fitted to a mini - reason being I prefer th look of the exits further apart rather than as they are on the MCS

[r1_kde]

you could fit a custom system not the stock TT as the battery box is in the way. the only reason I could see for having a valve is to control the noise or to allow the car to use one pipe or both. does sound odd and I have not seen that.

Try torque flow birmingham (very good) Torque Flow

Would leave you with a gap in the center of the bumper though

[MINI-Morgan]

Thats cool is that the butterfly should open at WOT too.

[brainycheddar]

I saw a video of a Nissan Skyline GTR- R34 that was specially tuned, with an automated iris in the tailpipe. I have no idea what it does (probably shakken regulation) but it just looked menacing. I couldn't figure out what company made them or else I'm sure I'd have one in my car ;p

Edit- found it!!!
http://www.nengun.com/hks/high-power-exhaust-ev-r
although I don't think they make it in MINI

[Ant FR]

butterfly on the 3.2 tt is also used on the R32 gold. Its to stop the booming that seems to happen on the 3.2 when cruising. So i think they are closed at anything up to 2500-3000rpm. then above that they open up with increased throttle.

Having said that, the first mods most R32 owners do is to remove the valve

[Nath316]

interesting

personally i like the opening and closing

you could paint it with heat resistant paint and have it like an eye winking at people or somesuch!

[James@fomsport]

carpisto and a few of the better aftermarket exhaust makers have this as part of many of their systems (usually on Ferraris, Lambo and porkers)

its operated via a remote control so if one night you feel like hammering home with thunder you can but say you have a long drive and dont want boooooom etc you can close it off (also helps your neighbors keep liking you)

[Nath316]

so this is purely a volume device then

it isnt a performance item or does the closed off zorst reduce performance

I know the better flowing the gasses the better the engine but if it is closing off an exit then all goes through the other one, surely that means that thereis additional noise?

[brainycheddar]

well from my understanding, even with 2 exhausts, and one plugged up at the tip, the pressure waves will flow through the piping leading to the plugged hole, in essence baffling the noise by taking the energy of that intense pressure wave, lengthening the wave, so the energy is still there, it's just spread out over a longer distance. Kind of like a breakwater in a harbor.

[MINI-Morgan]

What you want is one that maintains the exhaust back pressure at low revs and power and then as the revs build it opens e.g. like when you come onto SC boost.

[Nath316]

exactly so who is gonna make one?

[brainycheddar]

well, you can take an electronic exhaust cutout valve and an RPM activated switch (both from the hot rodder world) and do magic.

The exhaust cutouts I've seen are to block the exhaust coming out of the straight pipes and are switch activated, so drill a couple holes in one and have it inline with the rest of the exhaust, and have an RPM switch (most are made to run off a spark lead in a v8s, so divide your ideal rom by to and input that into the switch) so for example, you set the switch to 1500 rpm, and then as you rev past 3000 rpm the valve flips open. getting the proper backpressures is the tricky bit.

[Nath316]

can I have that in english please lol

[James@fomsport]

Quote: Originally Posted by Nath316 (original)

so this is purely a volume device then

it isnt a performance item or does the closed off zorst reduce performance

I know the better flowing the gasses the better the engine but if it is closing off an exit then all goes through the other one, surely that means that thereis additional noise?

in a word yes as Mini Morgan said having some restriction at lower RPM helps keep low end torque, but if it opens up later it will allow the engine to gain high end power the OEM Ferrari and Masseratti (and many others) systems work like this from the factory

[brainycheddar]

I just like the idea of an iris that opens and closes as you rev it!! If the exhaust routing wasn't so unique :- / , I'd try and get my hands on one of those bad boys.