hey guys,

I've looked through the forum and i couldn't find anything, but I know a lot of luxury cars especially those in Europe have a flap somewhere in the exhaust that closes during low rpm to reduce noise and drone and open up when the rpms build to create a better flow and therefore a louder exhaust note. Cars I know for sure have this is the R32, BMW 335i, and the TC (lol I know not luxury or European but they have this thing) I was wondering if our cars have one because it seems like my exhaust is really quiet until 3000rpm and it gets much louder.

 

I recall 2000 Maxima's had something like this--dual chamber with a valve that opened up with higher RPM. Supposedly it allowed it to be very quiet at low rpm yet have good flow at higher rpm. Here is some info:

http://www.nissanhelp.com/Models/2001/maxima/

"...the addition of a new variable capacity muffler derived from the one on the high performance Nissan Skyline GT-R. A special muffler flap valve, using high temperature aerospace spring technology and materials, opens at 2,000 rpm and above - reducing exhaust system backpressure. These changes helped increase the engine's horsepower from 190 to 222 and torque from 205 to 217 ft-lbs, versus the 1999 Maxima"

 

Interesting that must mean we have one too, I mean I don't think they would take out tech like that, any idea where it is located? Wait according to that it's in the muffler?

 

I highly doubt we have an exhaust valve flap.

 

I know what you mean.... Most BMW have this.
I think it was also related to more effiencey (emmissions) at low RPM.

If the G has it, it would be internal to the rear muffler(s).
When I installed my Magnaflow rears, there was definitely no external valve flap to deal with.

 

it might not be controlled, which means it could be pressure based and be totally internal to the can and you would not know its there unless u cut one open.



IE as RPMs build, the exhaust pressure builds and the flaps are regulated by exhaust pressure and open when the pressure reaches a point.

 

^ my thought as well.

 

Yeah I know most flappers are all controlled by pressure, I took off my mufflers I have Tanabe's but i was wondering because it's still rather quiet it won't be way up in the exhaust right?

 

No, I went over the system front to back.
The rear cans are the only logical place IF there's one at all.
My Magnaflows (rear only) sound sweet, much better than OE at idle.
They took a while to break in though.

 

Thanks Intgr8r, I really appreciate it I guess the Tanabe people really got thier act together and made an awesome set of exhausts lol.

 

FWIW...
We do some control work with pressure systems (not like this though)
& I believe for one of these flap systems to work properly, it would have to be near the back.
That way the system stays properly pressurized, with the pressure drop right at the back.

If the pressure drop occurred upstream, that would leave a low pressure exhaust system which probably wouldn't flow too well.

 

Thanks for the info Intgr8r, I just thought maybe there was a flap because after my HFCs, when the rpms drop only around 2.5-3krpm there is a whistle kinda sound, Adrian said it was the exhaust sucking air back in, but it's only at that range, so I thought maybe there is a valve or something that's not really fully closed or something so as the exhausts comes out there is this sound. Sounds like it's right after the cats though. Thanks for your help anyways!

 

At least for the Maxima, the flap was in the muffler. Some from the previous gen put these things on but I don't think it translated to an increase in power. I am pretty sure also that our cars do not have something similar but our stock exhaust aren't exactly quiet--nor was that a priority for a sports sedan.

 

On the 3 (before I changed the stock exhaust), the flap was in the muffler too. There was actually an actuator in the rear trunk quarter panel that was electronically controlled. Many people would disconnect it to make the exhaust a little louder, as disconnecting it would leave the flap open full time.