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Originally Posted by ksfrogman
The question of "what is the exhaust valve for?" has received so many different answers. The three answers I have received are:
(1) It modulates sound quality
(2) It closes at certain RPMs to attenuate the backpressure under conditions that would optimize torque.
(3) The combination of (1) and (2)
What Ryan at Eisenhaus said may be true. I honestly don't know the answer, because I need some objective proof. I am going to find out for myself once and for all.
I will run 3 Dyno pulls with my 330i, then I will disconnect and plug the line to the valve solenoid, and test again. I will post the results.
I also want to investigate ways to objectively quantitate the sound quality. This may prove to be difficult since I don't have a huge sound chamber with a decible meter. Anyone with ideas, please chime in.
Lastly, I will connect a vacuum gauge to the exhaust valve tubing via T-connector and see at what RPM the valve actually closes and reopens.
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Not a regular member here, but was reading through. The valve opens only in second gear onwards from around 3000 rpm, but I'm not 100 percent sure about the rpm. This is for acoustic purposes only (think of a trumpet) and torque isn't affected.
P.S. I had an internship at BMW SA in the acoustic section, that's how I know.