[SOLOMEK]

Rookie question I'm sure but I would like some insight on the ins and outs of this system.

I love the startup sound of my M235i but it goes away after a few seconds.

Also, does Sport or Sport + change the exhaust tone?

[Boba666]

I was told the valve stays closed until the catalytic converter comes up to operating temperature. The quicker it does this less crap goes into the air. You can easily disable it so you have more noise. M235 and m240 different. Someone stop me if I'm wrong but. m135 .run car listen for the valve opening then disconnect the wire going to the left tailpipe as you look at of from rear. m240 just disconnect the cable when car is cold before starting.
mperormance can doesn't have valve. which is counter productive to the cat if I'm correct

[MassNerd]

I don't think the valve has any impact to the warming of the cat. Closed vs open isn't changing the back pressure much.

You are correct that you can disconnect the cable when the valve is open to leave it open permanently.

[Ron Jeffries]

I'm so sad that my 2018 with MPE doesn't have the valve. I need more snaps.

[morphomeman]

Wait a sec! You get more noise at startup, when the valve is CLOSED. Disabling it will result in less noise at start-up and the same noise thereafter as you are getting now once the valve has opened.
Also, you will hear more noise when the car is stationary than when it is moving, because when you are not at rest, you are moving away from the noise.
I understand that some folks like noisy cars, though noise does not equal power or speed at all these days. Consider the Tesla.

[KennyFSU]

You can disable the valve when it is open (Sport+ mode and pull the fuse or the plug itself) so that it stays open.

[Boba666]

Apparently it's all down to the design of the back box.When you look at the exhaust from rear. The exhaust tip on the left has the valve. The exhaust from engine to back box enters way off centre towards the right tip (no valve.)
When on start up the extra noise created is because of A. The increased revs on start up.(warm or cold). This makes it impossible to notice the difference open/closed as you can't stop it doing the high rev start up..The valve is closed so back pressure is raised and all the gases exit just the right tip. This heats the cat as gases can't escape as quickly.The right tip exit is virtually directly opposite the pipe coming in from the engine. Bit like straight through. The valve is opened on the left when time or temp I don't know is reached. This corresponds with the revs dropping thus quietening the noise. Pretty damn quiet on tick over.
Now....when you use the throttle the gases with the valve open can flow through and out the left and right, you are basically now starting to use the actual back box for the first time since starting. Using the full resonance of the box. If you listen the sound created when the valve closed is a constant aaarhhhhh . Open it becomes more boomy, throaty, poppy. Fix it so its always open like in sport, sport plus . It will sound the same in eco etc. I had the back box internals changed. opening up the back box from above so from underneath no one BMW Inc can tell. makes it a lot louder. Cost £70 and better than mps. Now I can drive quiet with valve closed in eco/normal. sport/sport+ slot louder with more pops when you lift off the gas. nice not annoying.
sorry to go on. I'm more than happy to be wrong and learn something new. ha ha. pics show box other way up so that left is right. visa versa.Last pic is correct way up. It makes more sense looking inside.

[Boba666]

If anyone interested. This is how to do it.
made no changes to small compartment on left. Weld sleeve inside if you want louder..I wouldn't.
removed all wadding and made changes as in pics. You will like the difference. Save a £1000.

[Poochie]

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[XutvJet]

The reason the exhaust is so loud on a cold start is because the wastegate is fully open. This means a lot of exhaust gas is bypassing the turbine (essentially a muffler). BMW does this to improve catalytic converter light off. The exhaust valve opening and closing has little to do with a change in exhaust volume at idle, cold start, or light load.

[Boba666]

The original question was why the exhaust valve open and closed. we are talking about what happens when the gasses reach the cat and then back box with valve. Wastegate would be open on the basic assumption that you are not trying to produce boost on start up or idle.

[XutvJet]

Originally Posted by Boba666

The original question was why the exhaust valve open and closed. we are talking about what happens when the gasses reach the cat and then back box with valve. Wastegate would be open on the basic assumption that you are not trying to produce boost on start up or idle.

I believe the OP thinks the loud cold start up volume is the result of the muffler valve opening/closing. That is not the case. The loud cold start up is the result of the wastegate being open. When the muffler valve opens/closes, there is very little change in exhaust volume at idle, even with a catted DP and MP exhaust like on M235. I've run my car with the valve disconnected and in the open position and there is very little difference in exhaust volume when driving.

[Boba666]

The valve is just there mainly to heat the cat quicker.Sound wise if you drive normaly in sport, sport plus then fixing the flap open won't change anything in terms of sound. If you drive in comfort,eco then you will or should notice the difference..I modified my internals and valve open/closed is night/day. Closed you would never know. Anyhoo let the lad play and see what he decides. A bonus to disconnecting is your right tip doesn't noticeably get shit up. And in my case discoloured.

[XutvJet]

Originally Posted by Boba666

The valve is just there mainly to heat the cat quicker.Sound wise if you drive normaly in sport, sport plus then fixing the flap open won't change anything in terms of sound. If you drive in comfort,eco then you will or should notice the difference..I modified my internals and valve open/closed is night/day. Closed you would never know. Anyhoo let the lad play and see what he decides. A bonus to disconnecting is your right tip doesn't noticeably get shit up. And in my case discoloured.

I do not believe that the purpose of the valve is to improve catalytic light off. It wouldn't make much sense to vary the exhaust flow aft of the cat if your goal is to improve light off.

The valve opens and closes based on driving mode, throttle position, and load, and contrary to common belief on these forums, the valve is not always open in the Sportier driving modes. It is variable. IMO, the valve manipulation is for both sound and improved throttle response.

[Boba666]

That's how it works. And what it does. say BMW. You must not understand the mind of a German. Everything for a reason and that reason must be worth their time that's why we love our 240's.The very competent underdog .I like to described it as.