[The Bavarian]

I'm looking for some feedback as to whether this is how it should be working.

From a cold start, the exhaust noise is really loud. To the point I had a neighbor suggest I put a muffler on the car?
The RPMs start appropriately at around 1200 - 1300. Within about 30-45 seconds, the engine drops the RPMs to about 7000 and as it does the sound from the exhaust softens considerably.

At start up, I have watched the valve in the tailpipe. It is open the entire time. The vacuum hose is still attached and the wires behind the tail light are still attached. It never closes. I do have the Performance Power Kit on this car, so I assume this might be part of this modification.

Based on what I am hearing when it starts, it would seem there are other valves in the exhaust? It goes from an initial loud growl (as if there is no muffler at all) to what you'd expect to hear from a regular sedan.

Does this sound correct? What could be changing the sound coming from the engine? Next weekend I will try and make a video of this so you can hear for yourself.

[Nguyenhu0106]

correct me if im wrong guys but what i think is happening is that, when you have the performance kit installed that actually deactivates the rear actuator to the tail pipe.
but what you can do is.. before your start the car.. pull the rubber hose and see if there is any kind of vacuum when you start the car if not then that could be the reason for it.

and you may have to code your car to reactivate it or take it in the dealership

[MachWon]

Totally normal. The car is designed to idle higher for a bit on a cold start.

If you have a JB4 you might have the exhaust valve set to stay open 24/7.

[The Bavarian]

I totally understand the higher idle at start - makes perfect sense.
What I failed to mention is that once it idles down and the exhaust "notes" decrease, I am unable to duplicate the sound by running the RPMs back up. It's as if it's a different exhaust.

I will place a vacuum gauge on the line to see if it's trying to close the valve. I can tell you that I am able actuate the valve lever by hand and it moves freely. I can also apply vacuum to the actuator and get the valve to close.

I don't doubt that the Performance Power Kit overrides that valve.
What I am curious about is the change in exhaust sound from startup to a minute later and what other adjustments must be going on inside the system to impact this.

[ThEnder]

It's louder on a cold start because the waste gate on the turbo is open in order to quickly heat the cats.

[MachWon]

I believe that has something to do with the wastegate position on a cold start.

After the car quiets down, is the exhaust valve still open, or closed?

[The Bavarian]

Exhaust valve is always open.
Unless the valve might close during driving conditions, which I've not mounted a camera to see if this is the case.
Fully open, at cold start, at warm start and while punching the accelerator while parked, it doesn't move.

What does the wastegate do? I know the BOV diverts pressure away from the intake manifold, but not sure about this device does.

[MachWon]

Wastegates control boost. Not exactly sure what happens on a cold start but I assume the wastegates open fully, dumping the pressure from the turbos into the exhaust. Mine does the same thing as yours. Sounds mean for a minute haha.

[ThugzZ BunnY]

sounds like your car is acting up. you should probably take it to a BMW dealership. its definitely broken.

[The Bavarian]

Its time to have the rear brakes done, so I'll add this to the list of things to evaluate.

[Dann]

It's 100% normal for it to run at a higher rpm on cold start. Every car I've ever driven does it.
The exhaust flap should be shut on idle though so that would be one way of quiten it down.
If it's not shut at idle it will never be shut.

However the cat warming cycle only lasts 65 seconds so tell your neighbour it's normal and to shove it.

[kiel_dafo_kenyg_as]

On a cold start fuel is kept beeing injected even after ignition, causing a flame inside the pipes that helps heating up cats. The oscilating flame is what makes the growling sound that reminds a bit of a pulse jet engine