[David.m]

The stock exhaust valve closes at higher engine rpm, even in Sport+. I'm wondering why and whether keeping the valve open (eg by removing fuse) could adversely affect performance? My only mod at the moment is Fabspeed sport cat.

It would seem with the valve closed there is potential for the muffler to be a point of restriction as the inlet pipe diameter is substantially larger than the single outlet. I'm guessing any affect at the engine would be delayed while pressure builds up back along the exhaust pipe.

The Technical Training manual says "In the higher gears, the exhaust flap is closed in the critical ranges. The same applies in the upper engine speed ranges depending on the load". I've not been able to find more specific information as to when/why the valve closes but I can say that since I've removed the fuse to keep it open full-time I've noticed sustained spirited driving now leaves an even spread of carbon across the 4 exhaust tips whereas before the valve side tips would stay a lot cleaner.
Obviously the MPE and other after market exhaust valves operate differently and I've wondered also whether the performance gains of after market exhausts could be linked to the stock valve operation?

Any engineers out there who can educate me?

[Anthony1s]

To give quieter cruising sounds

[nioh_lbbm2]

Just a shot in the dark here but maybe at high rpm it is not compliant with US noise levels so it had to be closed to be compliant in all states

[cecaa850]

I've followed my wife in her Macan. When she comes to a complete stop I can see the exhaust valve open. As soon as she takes off from the stop it shuts. Seems opposite of what you would expect it to be.

[Anthony1s]

Originally Posted by cecaa850

I've followed my wife in her Macan. When she comes to a complete stop I can see the exhaust valve open. As soon as she takes off from the stop it shuts. Seems opposite of what you would expect it to be.

It depends what mode you're in. Comfort behaves kind of opposite of Sport+ mode. Here is the documentation OP is talking about.



Basically, in Comfort mode the flaps are closed until you're in a higher rpm/low gear range.

In sport modes, the flaps close when you are in higher gears/lower rpm range (not in higher rpm like OP said), which makes me assume it's to quiet the car during cruising.

Both modes have valves closed in highway cruising scenarios.

[PilotxERAU]

Originally Posted by David.m

The stock exhaust valve closes at higher engine rpm, even in Sport+. I'm wondering why and whether keeping the valve open (eg by removing fuse) could adversely affect performance? My only mod at the moment is Fabspeed sport cat.

It would seem with the valve closed there is potential for the muffler to be a point of restriction as the inlet pipe diameter is substantially larger than the single outlet. I'm guessing any affect at the engine would be delayed while pressure builds up back along the exhaust pipe.

The Technical Training manual says "In the higher gears, the exhaust flap is closed in the critical ranges. The same applies in the upper engine speed ranges depending on the load". I've not been able to find more specific information as to when/why the valve closes but I can say that since I've removed the fuse to keep it open full-time I've noticed sustained spirited driving now leaves an even spread of carbon across the 4 exhaust tips whereas before the valve side tips would stay a lot cleaner.
Obviously the MPE and other after market exhaust valves operate differently and I've wondered also whether the performance gains of after market exhausts could be linked to the stock valve operation?

Any engineers out there who can educate me?

I have Dinan exhaust res delete and fabspeed sport cat. Used BimmerLink to better understand valve behavior. Worked great since you can permanently open/close or auto (factory setting). This thought me hands on and answered many of my calve questions just through trial. Now I am looking at CAN FLAP controller for a more permanent value control solution.

[///M Houbi]

This one super sexy....