Some exhaust shots

[dcs2k]

left exhaust looks different from right exhaust.

[teagueAMX]

The right side has a control valve and bypass.

1. Yellow box - vacuum control device
2. Red Box - butterfly valve
3. Green box - butterfly valve bypass

No. 1 is controlled by engine speed. No. 2 is normally closed and No. 3 is used for exhaust gases when No. 2 is closed.

As engine speed increases, the butterfly valve opens to allow full operation.

Not sure why BMW would do this - maybe noise control?

[yabbanoname]

Hmm, should the surgical clamp method work too on this valve like on the 135i/335i exhaust ?

http://www.tyresmoke.net/forum/bmw-t...ncer-flap.html

[teagueAMX]

Originally Posted by yabbanoname

Hmm, should the surgical clamp method work too on this valve like on the 135i/335i exhaust ?

http://www.tyresmoke.net/forum/bmw-t...ncer-flap.html

Pretty cool link – thanks.

It confirms my thoughts on it, and that is you could disconnect the small rubber hose at the valve. Make sure you cap off the hose with a small screw that snugly fits in the hose, and then wrap it once or twice with some black electrical tape. Might be a good idea to put some tape over the valve opening as well just to make sure no dirt gets in there – who knows you might want to reconnect it someday.

The guys on the link indicated they successfully did this mod with no error codes.

The valve butterfly is normally open when the engine is not running. Disconnecting the hose will leave it in a permanently open position.

.

[yabbanoname]

That's where the surgical clamp comes in.
Disconnect the hose, put clamp on it, connect hose. Ready!


Thnx to http://www.billswebspace.com/

[twin turbo]

I pulled the electrical connection on my 335 coupe, made a noticeable difference in exhaust sound. I had no idea this car had a butterfly valve on the exhaust. I will look for the power harness.

[twin turbo]

Not sure which harness is which. I ended up performing the infamous "golf tee" mod that was popular on the 335's. I will take the car for a spin later tonight to see if it made a difference.

[teagueAMX]

Originally Posted by yabbanoname

That's where the surgical clamp comes in.
Disconnect the hose, put clamp on it, connect hose. Ready!


Thnx to http://www.billswebspace.com/

That clamp look like it would work pretty good. For many years I've used screws to temporarily block vacuum lines, now I'll have to get some of those clamps!

As far as the mod is concerned, I can't see this making a big difference in sound levels and you wonder why BMW bothered. Power levels aren't going to change much, either.

Looking at those complicated mufflers, it's a little easier to see how BMW's cars weight a bit more than say a Porsche. Multiply that across the board for many other components and you could come up with 200-300 lbs rather easily.

[yabbanoname]

Well, you can spare you the time doing this 5 secs mod, I did take her for a spin today, nice (nothing more than that) brumble, but I rather have the valve control the sound and kick in at a certain point. It sounds rather cheap this way.
And the low rev accelleation feels somewhat slower ...
Well the undo is also 5 secs of work

[teagueAMX]

Originally Posted by yabbanoname

Well, you can spare you the time doing this 5 secs mod, I did take her for a spin today, nice (nothing more than that) brumble, but I rather have the valve control the sound and kick in at a certain point. It sounds rather cheap this way.
And the low rev accelleation feels somewhat slower ...
Well the undo is also 5 secs of work

So, you did notice a difference in the sound levels?

Does it seem to you that performance is a bit weaker?

[yabbanoname]

Originally Posted by teagueAMX

So, you did notice a difference in the sound levels?

Does it seem to you that performance is a bit weaker?

soundlevel, louder at start, not really worth the change (maybe for better waking up the neighbours)
yep, somewhat weaker performance (low revs)

My advise: save your 10 secs change/undo time ;-)

[twin turbo]

I like the added burble. It will hold me over until the Eisenmann exhaust system is ready.

[cdeslandes]

Originally Posted by yabbanoname

Well, you can spare you the time doing this 5 secs mod, I did take her for a spin today, nice (nothing more than that) brumble, but I rather have the valve control the sound and kick in at a certain point. It sounds rather cheap this way.
And the low rev accelleation feels somewhat slower ...
Well the undo is also 5 secs of work

I did the mod recently, and didn't notice much difference in sound. But the engine seems to hesitate at low revs after a cold start. Lack of back pressure perhaps?
Anyway, back to normal as of tonight, we'll see if it runs smoother in the morning.