# BMW Exhaust Valves....



## r1 (Oct 31, 2002)

On the twin pipe exhausts there's a valve in pipe 2 that opens and shuts relative to revs presumabley to improve sound quality/volume at low revs.

However, mine has fcuked up and is rattling around like a bstard....anyone else had any experience on this?

Garyc - any further info on the valve? I'm assuming it's fairly important....otherwise I'd just rip it out with pliers to prevent a bloody dealer visit


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## garyc (May 7, 2002)

> On the twin pipe exhausts there's a valve in pipe 2 that opens and shuts relative to revs presumabley to improve sound quality/volume at low revs.
> 
> However, mine has fcuked up and is rattling around like a bstard....anyone else had any experience on this?
> 
> Garyc - any further info on the valve? I'm assuming it's fairly important....otherwise I'd just rip it out with pliers to prevent a bloody dealer visit


R1, I believe it's linked to VANOS inlet/outlet tuning, which optimises torque low down and also top end breathing for max power.

Despite what some of the people around here think, back pressure is a good thing for road engines and engineers tune and balance exahaust for a reason. I am not sure wether the flap is solely a noise abatement thing, or whether it is linked into exhaust tuning. Bit of both I suspect.

I shall have to follow one of our team 330is closely whilst they cane it to see if the flaps opens (and at what revs). Keeping up should not be a problem. 

Something tells me there won't be much discernable power delivery difference if you rip it out - probably a little more around town burble will happen.


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## coupe-sport (May 7, 2002)

> back pressure is a good thing for road engines


on a NA car yes...


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## garyc (May 7, 2002)

> on a NA car yes...


And forced induction too, as far as I know...


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## coupe-sport (May 7, 2002)

Its not really needed on forced induction engines as most of the time you dont have to rely on an cylinder scavenging to 'pull' the induction mixture in. The problem with a turbocharged engine is the turbo provides a large restriction in the exhaust manifold - apart from manifold design, the only other requirement is a free flowing system - you need to get as larger pressure differential across the exhaust turbine. Its then a balance of exhaust pipe diameter, to achieve a enough airflow to stop back pressure building up in the exhaust and reducing the differential across the turbine at high revs, against not making it too large, to slow down gas flow and and reduce torque off boost.

James.


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## r1 (Oct 31, 2002)

> R1, I believe it's linked to VANOS inlet/outlet tuning, which optimises torque low down and also top end breathing for max power.
> 
> Despite what some of the people around here think, back pressure is a good thing for road engines and engineers tune and balance exahaust for a reason. Â I am not sure wether the flap is solely a noise abatement thing, or whether it is linked into exhaust tuning. Â Bit of both I suspect.
> 
> ...


Hmm, I've leave it to the pros I think. If you follow a 330 you'll see the thing opening and closing through stop and start trafiic.

Mind you, 'around town burble' sounds fun. 8)


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## vlastan (May 6, 2002)

The same flap that the V6 TT has. How can it just fail? It is only a little round metal flap, that is held in the pipe by two hinges at opposite sites.


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## coupe-sport (May 7, 2002)

corrosion maybe - tends to happen in exhausts which is why they fall off eventually...


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## r1 (Oct 31, 2002)

> is only a little round metal flap, that is held in the pipe by two hinges at opposite sites.


Surely it wouldn't open then? :


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