[Dinh335]

Noticed this morning warming up car, that upon startup, smoke only comes out the right tail pipe (335). The right also has noticeably more soot. None out of the left one...of course after a few seconds or a minute they both don't blow any smoke...but wondering why it's just the right? anyone else with this?

[BMWforLife]

The left pipe has a flap that closes off the outlet upon start up, and once the engine is warmed up it will open and both pipes are flowing exhaust.

If you start the car and get out and listen, maybe even peer into the left pipe from a few feet back (don’t inhale the fumes) you can hear/see the flap open.

Also, it isn’t smoke, its water vapor. at least...I hope your car is not smoking lol.


many people disable the flap (known as the “golf tee mod”).

The flap is pretty much there to reduce noise at low RPMS

[n55x3]

Originally Posted by BMWforLife

The left pipe has a flap that closes off the outlet upon start up, and once the engine is warmed up it will open and both pipes are flowing exhaust.

This is completely opposite of how our N55 equipped motors and exhaust work.

Ours work exactly as the OP described and is normal.

On cold startup the flap opens until motor reaches a certain temp. I think our flap closes pretty quickly, like within a minute. Then it remains closed in normal MILD driving situations. Under hard throttle or anytime above 4k rpms the flap opens to reduce back pressure which ultimately increases performance and sound.

Totally normal to have one dirty pipe and one 'cleaner' pipe. I do agree on the flap mod though and it is something I've done on all our N55 vehicles, in one way or another. For 1 I like to have my pipes get dirty in symmetry and second, I like the sound of the exhaust when the flap is open all the time.

I haven't confirmed with a 335i (ours is due in a couple weeks) but I suspect this methodology is consistent across all N55 equipped vehicles.

[Teemo Panda]

It's normal.

[Dinh335]

cool- i assumed it was normal, so that's good...always curious on little things i notice on the new ride.

and yes, it's vapor not smoke

thanks guys.

[dcg71]

Yes its normal. Disagree on disabling the flap though. Its there for a reason, to balance back pressure between low and high RPMs.

[bcl0328]

Originally Posted by Teemo Panda

It's normal.

Never underestimate the power of the Scout's code.

[shivaswrath]

Originally Posted by dcg71

Yes its normal. Disagree on disabling the flap though. Its there for a reason, to balance back pressure between low and high RPMs.

Agree