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      12-08-2012, 09:09 PM   #31
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Drives: 2011 M3 E93
Join Date: Dec 2012
Location: Colorado

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Originally Posted by Hawker30 View Post
Originally Posted by DaveDee View Post

On your ideal exhaust scenario, what would you say the % reduction is from the valves open to closed? I just got the sport with x-pipe but I am concerned it is a bit too loud when driving in the neighborhood. I am seriously concidering the valved add-on but I would like to know if it makes a significant difference to the point where you are not turning heads at low idle.
On my set up (quad resonated Gintani with valved rear section)the idle volume is reduced by 5dB which in audio terms is around half plus. Of significance the tone changes (as the exhaust system is a tuned length of pipe and acts like a wind instrument closing a valve) to a higher octave so it does not rumble as much. On light acceleration the tone is a slightly higher and quieter sound.
From my basic understanding of exhaust systems a large diameter exhaust such as this has a huge volumetric space and at low RPM the exhaust gases don't accelerate from the system like they do at high RPM. Turbulence in the system from slow moving exhaust gas causes drone, and by adding the valves back pressure is increased so the exhaust gases escape at a higher velocity, hence no drone and a higher pitch.
At full throttle it's hard to pick the difference between valves open and closed, valves being designed more for low RPM round town driving and elimination as much as possible as drone. I would not be without the valves, they give an amazing having the best of two systems
Great facts. Very helpful thanks.