dlevi67

Quite. Wrong assumption that because a 535d has it, then a 530d has it too!

On a 535d it's located in exactly the same place as on a petrol engine, i.e. just inside the right hand pipe. The vacuum actuator is actually on top of the rear silencer box, visible with minimal effort just kneeling by the exhaust.

RealOEM does not show it on 530d - 218 or 231 bhp.

andy545

Interesting. it seemed the valve was there to help petrol engines build up some backpressure for torque down low (amongst other things).
Since diesels have heaps of this (torque) it seems to me the valve is more and more an emmisions control device along with possibly a noise abatement method.

After years there is still no definitive conclusion on this...

pinguhk

here is my tail pipe

dlevi67

When BMW introduced the idea (1995?) on E36 328i, it was presented as both enhancing lower revs torque and reducing noise. When closing the valve manually with my current car idling, the noise does decrease very noticeably, so perhaps that's the purpose.

I don't see how it could ever be an emissions control device, though. Except in as much as it may make combustion that little more efficient (higher torque), but the effect on overall emissions must be absolutely marginal.

aybeesea

When is the valve open and when is it closed?

ABC

AlwynMike

In theory, the valve should be closed at low revs, hence increasing exhaust back pressure to increase torque. This valve should open at high revs to allow all the exhaust gas to escape properly - and torque is less important at high revs. My father tells me that it was quite common on 1950's European engines to have a mechanical flap just downstream of the exhaust manifold, with a counterbalance weight external to the pipe - as revs increased, gas pressure on the flap forced it open against the weight. He says it wasn't very successful, as there were sealing and seizure problems with the flap (They always seized shut!!). I recall seeing such a contrivance on a mid 80's Trans Am, so our American friends were still using them at that time even on big lazy engines. Obviously the BMW encarnation of this device is somewhat more technical, and we must assume that it must do something significant, otherwise they wouldn't fit it, would they??? I can't see that it would simply be for better "Aural Tuning" to make the engine sound rortier at speed.

aybeesea

The valve on my 535d is open with engine off. Wrong or right?

ABC