Exhaust Note Explanation?

[RickMonet]

I borrowed the embedded clip from V8MAN "M Performance Exhaust" post (thanks!). Awesome sound clip with M Performance Exhaust.

Can someone explain what causes the "Braap" sound when throttle is lifted? Is it a result of the turbos or valves in the exhaust?

[savaho]

If you take a balloon and let the air out of it while stretching it I think you can duplicate the braap. lol Probably has something to do with the exhaust valves.

[Savory]

The F10 M5s do that as well. The exhaust on these turbo cars get quite hot. When the throttle is released, unburnt fuel ignites in the hot exhaust and gives that characteristic sound. Other cars have pops/crackles on overrun, but they seem much more controlled and brief on the M4. I attribute this to the ECU tuning

[Dawko]

IIRC Audi has similar burrpss for their RS cars. Simplified they drop a drop of gas in the exhaust/manifold or whatever which causes the burping sound. Might be the same for BMW?

[spool twice]

the backpop sounds great...its too bad videos dont show how unique the S55 exhaust sounds like in person. Videos dont capture how bassy the exhaust growl is (not v8 growl of course, but a nice straight 6 growl), mixed with the higher pitched whirr sound of turbos spooling through the exhaust, sounds pretty magnificent (I heard it in person this weekend), no where near weed-wacker status like most videos seem to portray.

[Ging]

Might be how they let off the boost pressure without blowoff valves just waste gates. The oem tuning might play with the valve timing(vanos) and valve lift(valvetronic) as you lift off the throttle and allow the manifold psi to blow through the cylinders straight to the exhaust/turbos pretty much giving the car huge overlap cam timing. The BRAAB noise caused by each cylinder opening to the exhaust. A bonus to this is its like a kinda anti-lag giving a big burst of hot gases to the turbos every time you lift. Thats if this is what they are doing???

[M4LAKA]

The Best is gunning it in tunnels and lifting the throttle and it makes a loud braap that just echos