What Does This Piece On The Exhaust Do? - BMW Forum

Slvr e39 · 05-09-2005, 09:53 PM

What does this piece do? Is this neccessary? Its a very heavy piece, and it seems to be louder when it is not on, but it may be just in my mind. Loss or gain in HP? Or is it just lame to take it off?

xsperf · 05-09-2005, 10:40 PM

my guess is that has something to do with if you have another exhaust pipe, but since you dont have another exhaust pipe(dont have dual exhaust) its blocked off.. and yes, it should be considerably louder w/it off

bryan1970 · 05-09-2005, 11:44 PM

i don't think it is just something to block the exhaust incase the car had duel exhaust becasue in the picture the opening for the piece goes towards the front of the car if i'm not misteaken. i don't know for sure what it is but my guess would be some sort of resinator to give the exhaust a sound that the engineers at the factory wanted.

Dirty_Tool · 05-10-2005, 12:32 AM

Actually it is meant for sound deadening. That whole funky design of there being like a "chopped off" exhaust is totally intentional and was developed for noise reduction due to the stricter noise laws in Europe. Its part of the Helmholtz noise cancellation system. Do a google search on it.

DT

Slvr e39 · 05-10-2005, 12:34 AM

so take it off it will be louder, and no hp loss?

Dirty_Tool · 05-10-2005, 12:36 AM

ya shouldnt see any HP loss.

DT

Slvr e39 · 05-10-2005, 12:56 AM

meh, it takes 2 seconds to take on and off, ill just mess around with it.

Dirty_Tool · 05-10-2005, 01:00 AM

cool have fun :-)

da_bull · 05-10-2005, 05:23 AM

A quick question: Does exhaust come out that hole when it is removed. If so, I would think you would be changing the tuning of the way exhaust is meant to go down the pipe. This gives an easy access for the exhaust to escape, but not neccessarily at the proper point. You actually could get less performance out of it. If a LOT of exhaust comes out that hole and there is not enough pressure to force out condensation from the heating/cooling down process, the back half of your exhaust may rust out over time. If exhaust doesnt come out of there, then you probably are ok.

I am sure BMW wouldnt have spent R&D money to make this piece if they didnt feel it was important to have on there. I know in the car audio world, adding weight to a panel makes that panel harder to rattle from the bass speakers, the whole idea behind sound deadening. I would search around a little more.

Slvr e39 · 05-10-2005, 10:17 AM

I understand the rust problem, thats why I am just going to take it off sometimes (if it does make a dramatic sound difference) if im going cruzin or whatever. It takes literally seconds to put on and off and no need to jack the car up. So i'm gonna get a second opinion on if its louder. I won't take it off for more than a day if I ever do it again. Why risk it?

Dirty_Tool · 05-10-2005, 11:34 AM

I should mention that when you spoke of removing this piece I assumed you would somehow cap off the exhaust side. I would never recommend anyone run their exhaust with a hole in it.

DT

Slvr e39 · 05-10-2005, 04:38 PM

please elaborate Dirty Tool. So I should cap off the exhaust pipe and just have that pipe? Or should I just take it off and see the difference? I have that dumb testing for school tomorrow so I have tons of time and no hw :-).

I know its pretty pointless to take it off, but ohwell... like i said before its not coming off for more than a few hours

Slvr e39 · 05-10-2005, 04:44 PM

just discovered that no air comes out of the hole with that weird heavy thing I have pictured above. When you cover the exhaust it gets pressure and blows the cap off, so this is pointless and lame. Dont try it...

Eric S. · 05-10-2005, 04:48 PM

Noise & vibration control was something I did in a previous career. The device you identified is definitely there to absorb unwanted noise, as in a helmholtz resonator as DT pointed out. Additionally, I suspect that, due to its size and weight, it may also serve to balance out vibrations in the exhaust pipe itself.

Speaking of helmholtz, there is a classic resonator chamber directly adjacent to, and similar in appearance to the muffler at the rear of an E39 540.

Likewise, there is a funny-looking appendix, uh, "thing", that provides a helmholtz cavity on the intake side as well. In the case of my 1999 540, it tucks up underneath the MAF sensor.

Good luck in your cause-and-effect research. let us know what you discover.

Slvr e39 · 05-10-2005, 07:39 PM

it doesn't do anything at ALL!