[SteveAus]

Has anyone noticed the unusal engine startup exhaust operation for the N55 in the 335i?
Even though I have had the car since April, and until recently, I had not walked around the back of the car immediately after starting the engine from cold.
I noticed that mainly the driver's side exhaust was emitting exhaust gases, and the exhaust from the passenger side was barely noticeable.
However, after a few minutes, both exhausts were working at the same levels.

Apparently, this is quite normal, and I believe this is the result of the exhaust putting backpressure on the engine for a faster warm-up.

If anyone has a better explanantion, I would be grateful if you could share it with me.

[drjekl]

Unsure of how the exhaust setup is on the F30 335i's, but on the E9X they had a flapper valve on the passenger side muffler.

On cold starts this would close to enable warming up of the cats i believe for emission purposes and reduce nvh. Sounds like the F30 may have a similiar setup.

[MD335]

I love the noise it first makes on cold start. A nice burbly sound, especially in the garage, but it dies off pretty soon after when the exhaust flap opens. Maybe it's time for M Perf. exhaust?