Just wondering why BMW incorporated such cable into their mufflers?

Does it mean once opened muffler turns to straight flow? How is it controlled?

How's the internal of the muffler as compared to non valved muffler version?

It's vacuum controlled and ostensibly is meant to provide extra flow under heavy acceleration. How effective it is? 🤷‍♂️

 

I always thought it was just a noise tuning thing- give it a bit more growl down low,
with less fart can overtone off idle...

t

 

Curious to know its internal stuffs as compared to the non valved ones.

 

And does it sound just like the non valved ones? Or louder?

 

There is no non-valved version, only mufflers without valve. Big difference.

Stock 330i muffler has the valve. Sport muffler also has a valve. Perfomance package muffler doesn't have a valve. Performance muffler also doesn't have a valve. All 4 of these are different from each other (not because of the valve but because they are different mufflers).

You can just disable the valve on the 330i and sport muffler. By now they should almost all be disabled anyway due to getting stuck.

If you want more sound I would just get a sport or performance package muffler.

 

By now they should almost all be disabled anyway due to getting stuck.

haha, made me laugh,

Yes it is sound control
helps with startups too so that you wont wake up the neighbors.
My stock exhaust valve had a rattle when taking left turns and accelerating lightly when the car was only a few years old.

then the golf tee mod was born in like 2002-2003 which fixed my issue until I got the Rogue DMS
For performance, replacing the heavy section 3 with a dual muffler system (on the 330s) was the only performance benefit
it just happen to come with great heavenly sound.

Only after super charging and then uncorking the stock headers with technik headers did I see some real horsepower gains.

 

On my 330i, the valve was stuck open when I bought it. It didn't seem loud to me. But after I freed it up, the valve would close at idle and light throttle, to (presumably) make it quieter. Personally I don't see the point, unless you're extremely sensitive to exhaust noise.

Edit: I forgot about the idle flare at start-up. That could be another purpose for the flap.

 

Oddly, 325xi has the valve, 325i does not.

Bmw make no sense.

t
was it a noise reg? The stock cars are pretty quiet, it seems...

 

Oddly, 325xi has the valve, 325i does not.

Bmw make no sense.

t
was it a noise reg? The stock cars are pretty quiet, it seems...

Does it? Weird. I wonder if it's the same one as the 330i?

EDIT: It is, and it's also used on the 325i M56 cars.

 

What I was taught at BMW:
The installation of the valve was a small part of the (EU4?) package. It was to reduce vehicle noise in inner-city uses.

Under less than 50% load the butterfly valve stays closed. Under higher demands, the vacuum controlled butterfly valve opens.

 

Mine is a EU4 package (meant for Spain) and it doesn't have the valve. It is very quiet though.

 

Yours is a 325Ci? That's what we were just discussing, only the SULEV and AWD 325is got the muffler with the flap.

 

In this case, the xi in question is an xit. Wagon, even.

t

 

My 330xi is not quiet. It's not loud but definitely not quiet. I wonder if it has an after-market exhaust. When I first read this thread, I thought maybe my valve was stuck open but since it doesn't have such a thing...