06-18-2011, 04:26 PM | #1 |
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35i vacuum operated butterfly valve on exhaust?
I noticed today that one of the exhaust lines on my 35i has a vacuum operated butterfly valve to open and shut it. Has anyone else noticed that? My vette has the same thing, when it opens around 3500 rpm it provides a less restrictive flowpath through the muffler. I'm wondering if the X3 one does something similar?? I've not read anything in the literature about this feature. Shocking I know!
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06-18-2011, 05:38 PM | #2 |
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Yes, there is a lot of info on this on the various forums here, and many people hardwire it by blocking the vacuum line. As far as I know, this valve is for noise control only.
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06-18-2011, 05:45 PM | #3 |
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06-19-2011, 01:24 AM | #4 |
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The valve is mostly for noise control at low rpms to prevent "droning" in the car. Some people have speculated that it also is used to slightly increase the exhaust restriction to heat up the catalytic converters after start up to reduce emissions, but given the [low] exhaust flow at very low rpms that is very unlikely.
To meet exhaust sound level regulations in many countries, some aftermarket "performance" exhaust systems also use the control valve. One performance exhaust system maker (3DDesign) says this about the valve: What is the Control Valve? The control valve is a simple butterfly valve that is actuated using the pressure from the vacuum lines. This valve controls the exhuast efficiency, volume and torque characteristics. Some BMW models have factory valve systems in place. The factory computer determines the timing for the opening and shutting of the valves. For instance (335i model): - Always closed on neutral shift - Opens at 2000 RPM on 1st shift position - Opens at 4000 RPM on 2nd shift position Opening and closing are controlled according to many different parameters (such as the degree of throttle plate opening) Factory vacuum lines and settings for closing and opening the valves are used for all 3DDesign exhaust systems as the design of the exhaust has been cleverly developed to allow for expansion of these settings for better performance characteristics. Since the factory exhaust systems (where applicable) has similar valve systems, the installation is simple and no extra modifications are needed. Plugging the vacuum line will make the car louder at low rpm and part throttle, but since the valve already opens up completely at full throttle, it won't make the car any faster. |
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05-29-2015, 12:01 PM | #5 | |
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Drives: 2009 BMW 335i (E90)
Join Date: Sep 2014
Location: Texas
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05-29-2015, 01:10 PM | #6 | |
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First of all, if you are curious what the before/after sound will be like, turn on your car, then go to the back, and look at the exhaust pipes. You'll see the metal valve attached to the outer pipe, with a little metal arm / actuator outside of it, and a black rubber line attached to it. You'll see the metal valve attached to one of the pipes, with a little metal arm / actuator outside of it. By default, that arm is extended which keeps the flap closed. If you push it in with your thumb, it will open the flap and you will hear what it would sound like. Note that if you do this test when the engine is cold, it will sound louder than under normal operating temperatures. Unlike in the E9x series, where vacuum is used to keep the flap closed, and by Disconnecting the vacuum line, the flap will remain open, is the opposite in our cars and the E6x ones (what I used to have). There is a vacuum line coming from the engine, going to a little electrical valve controller behind the trim panel on the left side in the trunk, and there is another line going down to this exhaust flap valve. All you do is disconnect both lines going to this valve controller in the trunk, and connect them to each other using a 1/4" coupler, and that puts constant vacuum on the exhaust flap, therefore keeping it open all the time. You can reach the electrical controller by just opening the trim panel, however there was in a lot of room to work and the lines are on pretty tight, so I took out the plastic bucket that was there, which is held in by a few plastic rivet type fasteners, and a torx screw. . Last edited by Lotus99; 06-01-2015 at 03:45 PM.. Reason: Added pic |
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07-25-2019, 10:31 PM | #7 | ||||
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08-10-2019, 04:36 PM | #8 |
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Immediately after a new turbocharger was installed on my 2011 335i, I noticed a loud low-frequency growl noise only when I accelerate. The repair place told me that my right faulty muffler value could be causing that problem. Anybody agree or disagree with that assessment? Thanks
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01-22-2020, 08:00 PM | #9 | ||
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09-19-2021, 05:55 PM | #10 |
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Hi fellow Beemer owners. First time on the X3 site. Have an E46 m3 and a new 2021 335i. Unfortunately my father passed away and left his baby (2016 X3 35i) to me.
My question for you experts, is that the car now is very loud on startup. No other CEL, MIL lights at all. Car drives fine but just annoyingly loud on startup. I have driven this care a 1000 times so I know how the 300hp engine sounds on cold start. But it is much louder than normal. Since neither of my other cars have a butterfly valve on the exhaust, do you guys think this could be the culprit? Full caveat, the car is located in CA and I am in NJ, so I am long distance diagnosing this. Any help would be appreciated. |
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09-23-2023, 05:29 PM | #11 | |
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