[maddmatth]

Originally Posted by STR8-6IX

yes. one side of the exhaust closed = more pressure for exhaust to escape (backpressure)

the flap opens at higher revs to allow the engine to breathe. so at low RPM's the back pressure is to help with torque. not a huge difference, but it helps the engine below 2000rpm

It's purely for noise control. PE exhaust doesn't include it.

[prima_materia]

Originally Posted by maddmatth

It's purely for noise control. PE exhaust doesn't include it.

Yeah, this is what I'd read in numerous threads. That's why I had mentioned a few posts back that if disabling the flap to keep it open was an issue, then how come the aftermarkets don't include it, just like the PE [like you said].

I know with stock exhaust, catless DP, and that flap open, tuned, sounds damn good.

Also, to quote shiv from a multi-year thread:

Originally Posted by shiv@vishnu

Exhaust backpressure is always an evil thing in turbo engines. Turbos are powered by the pressure differential between both sides of the exhaust turbine. The bigger differential, the better response time. You want max exhaust pressure on the inlet side of the turbine. For the most part, you do this by sizing the runners in the exhaust manifold properly and by coupling the turbo as close as possible to the exhaust port. The exhaust pressure on the other side of the turbine is kept low as possible by simply using the least restrictive exhaust system possible given the set of real-world constraints (noise, emissions, fitment, etc,.)

Cheers

[alddiem415]

Originally Posted by Trelos

Someone from jersey selling one for $800

http://www.e90post.com/forums/showthread.php?t=1363642

I saw that.. I texted him already.. Thanks for the heads up.. this might stick out and idk if the 4" tip will fit the msport bumper..

[STR8-6IX]

Originally Posted by maddmatth

It's purely for noise control. PE exhaust doesn't include it.

do all BMW's have it? my 2011 528i does not have a flap in the exhaust system, but it makes some sort of valve fluttering noise just above idle.

[maddmatth]

Originally Posted by STR8-6IX

do all BMW's have it? my 2011 528i does not have a flap in the exhaust system, but it makes some sort of valve fluttering noise just above idle.

Maybe. My 1998 E46 328i had it and it worked just like the one in the 335i.

[Trelos]

My 2000 E46 330 had one...for like 1500 miles till I put a Dinan exhaust on it.

[alddiem415]

Brand new for $1300 shipped
From michael hall

Do anyone know him?

[alddiem415]

Anyone know this guy or bought stuff from this guy?


If i go dp route with stock exhaust,
What dp should i get? What tune?
Just dont want any check engine light on
And i want to make sure that i'll pass nj emissions

[Mingwan]

I'm sure the PE mod was mentioned...

Just go with the legit performance exhaust. Sounds better. It produces a better quality sound.