So some of you may know, my brother just bought a 98' 328is. It is super nice and has a really nice sound to the exhaust. But I dont think the sound is stock. So I looked at the exhaust and there is a valve in one of the pipes. (see picture 1 "valve open") When the car is off, in neutral, or the when the revs are really high, it is open. When the car is in gear, and crusing normally, it is closed (see picture 2 "valve closed) Is this thing stock? Bad for HP?
Im 99.9% sure its stock. I think it had something to do with the california smog laws. But when you give the car full gas it should open so when you need the power it should all be there. Not sure though.
im 100% sure its stock. i was told that it closes to supress the sound of the exhaust, to make it more quiet when flow isn't important ie idle, cuising speeds. but opens duing full throttle or high revs to allow better flow
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Word to -pimpin328is- and Kevin325i. Both very correct.
Good for HP. Quiets the exhaust when power is not needed. Helps low end torque with added backpressure.
If you fold down the rear seats, roll up the windows and turn off the air and the radio, listen carefully, you can hear the air pump opening and closing it. It's pneumatic.
That sums up this question. Thread closed.
That valve pretty much creates back pressure for your exhaust system... and thus your engine... unless you give your engine more air.. (intake).. and then tell your ECU to use the greater air supply.. and then a more free flowing exhaust ( remove valve maybe or a new performance exhaust) Removing that valve will decrease the back pressure on your engine.. which is needed for low end torque like what was said above...
Originally posted by dutchbmw@Jan 2 2005, 07:12 AM I've just read about the new 535 diesel that has some kind of valve too. They say it's for quiet (not sure on what rpm or speed) the car some more.
Right now I have the valve disabled on my 328is and it sounds a lot better but there is a small amount of torque in lower rpms that is lost. I really don't care because if I want to go fast im above 400 rpms+. The valve is closed under 2500 RPM and open above that. It is for noise suppression and backpressure. Now that I have just installed the M50 intake manifold I am going to reconnect it to see if there is a difference with it on... So far it sounds really awesome with burbley lil pops like a rally car lol.
If you are wondering how to disable it and have it open all the time for a deeper bass'ier sound just look under your car and unplug the vacuum line that goes into the exhaust, then plug it up with something like a golf tee.
Finally open the trunk, lift the carpet up and at the bottom left you can see the vacuum line. Pull an inch or two of it up so the vacuum line is not hanging down near the ground. This can easily be reversed in 1 minute and make your esxhaust louder and deeper sounding
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