BMW vacuum exhaust baffle.

Rha

Rha

Zorg Guru (V)
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British Zeds
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Oct 26, 2014
Points
181
Location
Hemel Hempstead, Hertfordshire, England.
Model of Z
Z4 coupe sport.
Hi everyone, was just thinking does anyone have any idea why this sound deadening flap was fitted, I'm thinking it's not just for our ears to pick up on and maybe it got something to do with lower end torx. They say when you fit a straight through exhaust you loose a little bottom end torx (with loss of back pressure) that being the case I'm thinking BMW were maybe trying to give us the best of both worlds, as in the baffle causes that bit more back pressure in lower rev range and opens to speed up the exit of gases at higher revs which would be beneficial , having said that I seem to recall the introduction of similar baffle being built into the latest Aston, correct me if I'm wrong but would Aston really put one in if it didn't enhance performance let alone that cracking DBR sound. Yeh or Nay.:confused:
 
Rha said:
Hi everyone, was just thinking does anyone have any idea why this sound deadening flap was fitted, I'm thinking it's not just for our ears to pick up on and maybe it got something to do with lower end torx. They say when you fit a straight through exhaust you loose a little bottom end torx (with loss of back pressure) that being the case I'm thinking BMW were maybe trying to give us the best of both worlds, as in the baffle causes that bit more back pressure in lower rev range and opens to speed up the exit of gases at higher revs which would be beneficial , having said that I seem to recall the introduction of similar baffle being built into the latest Aston, correct me if I'm wrong but would Aston really put one in if it didn't enhance performance let alone that cracking DBR sound. Yeh or Nay.:confused:
Click to expand...
Just saw this on another forum:
http://www.bimmerforums.com/forum/showthread.php?1832748-Exhaust-Baffle
 
As I've always understood it's purely for noise reasons. Doesn't have any perceived effect on the engine, just makes a bit more noise when moving along. Probably done originally to appease some European regulation on noise.
 
I was thinking of posting along these lines as I put on another post that auto box cars do not have the flap and @t-tony posted back that his auto has the flap. Just checking on real OEM and with my serial number it shows a different rear silencer which also has a vibration absorber bolted to it.

Rear exhaust for my serial says not for auto.
http://www.realoem.com/bmw/enUS/showparts?id=CN52-EUR-06-2000-Z3-BMW-Z3_30i&diagId=18_0383

Rear silencer only for auto.
http://www.realoem.com/bmw/enUS/showparts?id=CN52-EUR-06-2000-Z3-BMW-Z3_30i&diagId=18_0432

But checking yr2000 2.0 shows the exhaust flap fitted and no difference for manual or auto.

Mine has all the parts of the vacuum side and electric valve fitted but nowhere to connect to. the plot thickens.
 
GazHyde said:
As I've always understood it's purely for noise reasons. Doesn't have any perceived effect on the engine, just makes a bit more noise when moving along. Probably done originally to appease some European regulation on noise.
Click to expand...

Thanks Gaz, your more than likely spot on, :thumbsup:still wondering about the Aston though. Maybe the BMW designers had stumbled on something long before Aston could be bothered with appeasing the petrol heads who thought their Astons weren't loud enough. One can only surmise.:cool:
 
Hi @Rha the valve in the Aston bypasses most of the exhaust silencer when open. It isn't just a flap in the tail pipe. There is a separate set of pipes out of the silencer routed into the tailpipe and the valve is a changeover valve.

looks like this.
AM.webp
 
I've been looking at TIFF's early Z road test and he mentions the exhaust note, maybe they took notice after the first batch. As far as I'm aware BMW didn't have the exhaust length on the Z to get much out of it. Maybe we should all add a couple of feet out the back with a Long Vehicle sign on it. =))
 
Rha said:
Hi everyone, was just thinking does anyone have any idea why this sound deadening flap was fitted, I'm thinking it's not just for our ears to pick up on and maybe it got something to do with lower end torx. They say when you fit a straight through exhaust you loose a little bottom end torx (with loss of back pressure) that being the case I'm thinking BMW were maybe trying to give us the best of both worlds, as in the baffle causes that bit more back pressure in lower rev range and opens to speed up the exit of gases at higher revs which would be beneficial , having said that I seem to recall the introduction of similar baffle being built into the latest Aston, correct me if I'm wrong but would Aston really put one in if it didn't enhance performance let alone that cracking DBR sound. Yeh or Nay.:confused:
Click to expand...
For the amount of torque you'd gain by shutting down one side I don't believe you'd even be able to notice any difference at all, as @FRANKIE LINK it's just to quiet things down at idle. JIM
 
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Rha said:
I've been looking at TIFF's early Z road test and he mentions the exhaust note, maybe they took notice after the first batch. As far as I'm aware BMW didn't have the exhaust length on the Z to get much out of it. Maybe we should all add a couple of feet out the back with a Long Vehicle sign on it. =))
Click to expand...
Or perhaps a set of custom long tube headers and eliminate the need for the sign?? Pick up a few HP also along the way! JIM
 
Brian4 said:
Hi @Rha the valve in the Aston bypasses most of the exhaust silencer when open. It isn't just a flap in the tail pipe. There is a separate set of pipes out of the silencer routed into the tailpipe and the valve is a changeover valve.

looks like this.
View attachment 16585
Click to expand...

Great reply Brian, knew someone would get to it in the end, don't stop me thinking they did it cos they knew other makes sounded better, now they've really started something, let's get rid of our boxes and go straight through with light foot on the gas peddle in built up areas we might just get away with it.:happy:
 
I want to run a true dual exhaust system with a set of long tube headers and see what shakes out! JIM
 
One of my friends has an electrically operated valve in the main exhaust that will totally bypass the silencers and the bare pipe is routed out the side of the car. It sounds petty rough really but stupidly loud. Volvo T5 engine running 300+hp
 
Brian4 said:
One of my friends has an electrically operated valve in the main exhaust that will totally bypass the silencers and the bare pipe is routed out the side of the car. It sounds petty rough really but stupidly loud. Volvo T5 engine running 300+hp
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That must sound interesting, love a 5cyl but no silencers at all could be a bit much! Any video clips!

Here is a clip of a 2.8 Z3 with that bypass valve fitted but I think still uses the middle box, sounds like a mini TVR.
Turn up the volume!
View: http://youtu.be/kCIGcjwFVao


Some pics of how it's done here:
http://www.zroadster.net/forum/viewtopic.php?f=15&t=42330
 
hard top said:
De-cat is the way to go, I did it on one of my Mercs, more power, less fuel consumption and a better sound out the back.
Click to expand...

Dead right HT, and I know people gone down that road, ok if you don't mind refitting every year for the Mot which I'd find a bit of a bind, which only goes to show that I'm not the petrol head I should be.:meh: If a kit came up that would bypass the cats on a switch I would be interested at the right price, don't know of one yet though, bet there's one out there at a price.:rolleyes:
 
Rha said:
ok if you don't mind refitting every year for the Mot
Click to expand...

I did not have a problem with that as it was a German all singing and dancing 190E import.
Nothing on the paper work or on the stamp under the bonnet about it having a cat.
 
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