Any power difference exhaust flaps open or closed?

[spikes111]

Is there any power output or performance difference between having the exhaust flaps (factory or aftermarket) open or closed?

Thinking about doing the flap mod or getting one of the flap controller units so got to wondering if there's any difference between open and closed flaps other than sound.

Thx

[CanAutM3]

Originally Posted by spikes111

Is there any power output or performance difference between having the exhaust flaps (factory or aftermarket) open or closed?

Thinking about doing the flap mod or getting one of the flap controller units so got to wondering if there's any difference between open and closed flaps other than sound.

Thx

In theory, open valves provide less backpressure and less backpressure can contribute to the turbos providing more boost. However, since boost level is ECU controled through the waste gates on the S55, there is no more power to be had with the valves open; unless running a very aggressive tune that maximizes the turbos. Further, turbos are able to spool up a little faster with less backpressure, however I am not sure it will be noticeable from the driver's seat.

You will more than likely not have less power by running with the valves open.

[BMWJ]

don't the valves always open under full throttle? except maybe sometimes in efficient mode?

[8600RPM]

Originally Posted by CanAutM3

In theory, open valves provide less backpressure and less backpressure can contribute to the turbos providing more boost. However, since boost level is ECU controled through the waste gates on the S55, there is no more power to be had with the valves open; unless running a very aggressive tune that maximizes the turbos. Further, turbos are able to spool up a little faster with less backpressure, however I am not sure it will be noticeable from the driver's seat.

You will more than likely not have less power by running with the valves open.

Why would dps make power on stock car then

[AlterZgo]

Originally Posted by 8600RPM

Why would dps make power on stock car then

Downpipes will make noticeably more power on an otherwise stock car. More so than any cat back exhaust system alone will give you.

[Ggeezer]

Originally Posted by 8600RPM

Why would dps make power on stock car then

Because they remove exhaust flow restrictions caused by having catalytic converters which reduces backpressure.

[CanAutM3]

Originally Posted by 8600RPM

Why would dps make power on stock car then

My understanding is that the downpipes remove a significant amount of backpressure that also translates to a reduced pressure upstream of the turbos. This allows for better scavenging of the cylinders and in turn better cylinder filling (volumetric efficiency).

[8600RPM]

No sucwouldn't thst apply to any reduced back pressure

[Hawaii i8]

No difference that I can sense, I've been running with the mod for nearly 3 months now. This car has so much torque I can't really use what I got never mind more :-)

[spikes111]

Do the flaps stay open no matter what in Sport and Sport+? Or do they sometimes close as well?

Same question but reverse for comfort mode - is it always closed in comfort mode?

[CanAutM3]

Originally Posted by 8600RPM

No sucwouldn't thst apply to any reduced back pressure

Yes, in principle it does.

However, I believe the reduction coming from opening the exhaust flap is so small it should make little difference in the pressure upstream of the turbo, especially at low RPM. At least that was my thought when I wrote my OP.

[CanAutM3]

Originally Posted by spikes111

Do the flaps stay open no matter what in Sport and Sport+? Or do they sometimes close as well?

Same question but reverse for comfort mode - is it always closed in comfort mode?

[mc3456]

Originally Posted by CanAutM3

My understanding is that the downpipes remove a significant amount of backpressure that also translates to a reduced pressure upstream of the turbos. This allows for better scavenging of the cylinders and in turn better cylinder filling (volumetric efficiency).

What do you figure the performance benefit of down pipes with sport cats are...half the gains of catless down pipes?

[Hawaii i8]

Originally Posted by spikes111

Do the flaps stay open no matter what in Sport and Sport+? Or do they sometimes close as well?

Same question but reverse for comfort mode - is it always closed in comfort mode?

After the mod valves are open 100% of the time, just like god intended!

[spikes111]

Originally Posted by BigIslandM4

After the mod valves are open 100% of the time, just like god intended!

Right. I was asking about the factory setup (pre valve mod). Thanks.

[CanAutM3]

Originally Posted by spikes111

Do the flaps stay open no matter what in Sport and Sport+? Or do they sometimes close as well?

Same question but reverse for comfort mode - is it always closed in comfort mode?

From the Sound and Exhaust System Deep Dive thread

From the outside-vehicle perspective, there is a distinct difference in the sound emitted when the exhaust valves are closed and when they are open. For control purposes, we vary the engine characteristics; this allows us to open and close the exhaust valves in accordance with variations in engine speed and load conditions and corresponding with the selected drive mode.

For instance, if you select the COMFORT mode, the exhaust valves are fully closed in the lower revs ranges. If there is a greater load demand at higher engine speeds, they open up. When driving with a constant load in COMFORT mode, the valves generally remain closed to achieve a maximum level of everyday comfort over long distances.

In SPORT and SPORT PLUS modes, other engine characteristics are selected for controlling the exhaust valves. At lower gears, the exhaust valves are always open, while when higher gears are selected under constant driving conditions, they are closed; however, if the load conditions change accordingly, they open up in a flash. There are also ranges in which we have chosen to close the valves, for instance at low engine speeds in high gears. In these ranges, which are frequently selected in the automatic mode of the M DKG Drivelogic for driving at maximum efficiency, the exhaust tract in turbo engines would have a tendency to drone if there were no damping.

[8600RPM]

Originally Posted by CanAutM3

Yes, in principle it does.

However, I believe the reduction coming from opening the exhaust flap is so small it should make little difference in the pressure upstream of the turbo, especially at low RPM. At least that was my thought when I wrote my OP.

Most impressed with your intpretation skills as I re read that and couldn't figure it out for a minute lol. Damn cells.