s4iscool

550 LCI does not have it. This is the main area that the sport exhaust gets a different tone. Mod your pre LCI 550 flap, and you get the same sound, which is just a little more grunt down low.

s4iscool

Actually affects power delivery as well.

pennetta

Just looked and mine has it, I would guess the non-sport 550's have it too. I don't think it's a EPA or a DOT thing because other cars have louder exhaust. I think more non-enthusiasts buy BMW's than enthusiasts so they keep the exhaust note tame.

Rizbel

Please explain. Thanks.

pennetta

It would affect both torque and HP. A more restrictive exhaust (less noise less exhaust gas flow) benefits lower RPM torque and a less restrictive (more noise and exhaust gas flow) benefits power in higher RPMs. This is called an active exhaust or a power valve. I have one on my Harley too.
It gives better low end and better top end at the expense of a little more complication.

bigbadbull

I know on the R32 and the Porsche It DOES affect power , and there are dyno graphs available to prove it.

On the R32's (MK IV) in first and second gears ( since can't hit 45mph at all) it is closed and there is about a 10-15 hp drop from when it is open in 3,4,5, and god for bid 6th. There is also around a 15-20 ft lb increase in torque, when it is open. I know this sounds crazy , but apparently it puts a ton of back pressure on the engine. The first thing most R32 owners do is to crawl under the back in with a Fast tie and clamp it off, or go high tech and put a hidden 3 position switch in ( open all time, closed all time ( for high way cruising above 80mph), and normal 32-3500 rpm @ 45mph). If you removed it entirely, you would get an OBD II emissions fault. So if you put an aftermarket exhaust in ( drops some serious weight out over 70-100lbs difference) you still have to clamp the solenoid feed line with a fast tie. Another note is that it never really opens all the way , so a system with out one got pretty decent gains over the factory exhaust ( along with the weight drop)

On the 911's if you get the sport package or I think the X50 option ( this is from memory so don't quote me) there is a factory installed sport button that opens the exhaust up for more noise and power.

It may help for better fuel econ around the city, and lower noise, but with a detriment to power.
I forgot to look on my 08 535i sp pck, but if there is one on it, being a boosted motor I would assume it would make a big difference in the lower gears with back pressure and restriction.

pennetta

This is common knowledge, there is a balance between the intake and exhaust pressures that affects the tune of an engine. I used to race cars and motorcycles and know some people that installed a loud low restriction exhaust system that sounds very fast but it actually makes less power.

BMW engines are in a high state of tune and you need a dyno to know if you have extracted more power out of them because of modifications. Other than the turbo 335/535/X6 its hard to get appreciable increase in power even with dyno tuning, even if Dinan is doing it.
I just replaced my Harley exhaust system to get better sound and more power. I bought a balanced kit from S&S (kind of like Dinan of the Harley world) that included mufflers and a low restriction air intake, S&S did the dyno time and I just bolted everything on.
If you want more details let me know.

Bteljuice

humor me for a second, but does my 520i have it.If yes, let me remove it at once.

Bteljuice

mmmm,as i understoodm it only comes for V8s and the tt v6?

bigbadbull

That is kinda the point why I have yet to put a after market exhust on my car, most manufactures say the 545/550 one will work , or a custom build magna flow... but they really have not taken the "Flapper" in to effect especially on the I6tt... How will this effect the back pressure and over all tune.

Also Do you get an OBD II code if you take out all the solinoid / air pump/ gass line out, or do you just cap it/ crimp it... and ignore it.