muffler valve/golf tee alternative---

[Wpcmac]

Pardon my ignorance, but how does this improve HP? If it improves HP and MPG and has no drawbacks, why wouldn't BMW have the stock setup like this?

[X3eme]

Originally Posted by Wpcmac

Pardon my ignorance, but how does this improve HP? If it improves HP and MPG and has no drawbacks, why wouldn't BMW have the stock setup like this?

The unrefined, non-BMW like sound is the drawback... to BMW. I kinda like it.

[judybe83]

max HP increase... not going to happen with this mod, the valve is open under WOT conditions

MPG increase... maybe a .01 increase in you do a lot of red lights and stop signs

but don't you just luv the sound

ab

[noncom23]

So Cleaner, you have to teach now. What are the potential hazzards here. Want some input
before I do this to my 2006.

Originally Posted by The Cleaner

Why are we doing this exactly? My understanding of the system is that it helps heat up the cats and O2 sensors when cold.

[dkl]

Originally Posted by noncom23

So Cleaner, you have to teach now. What are the potential hazzards here. Want some input
before I do this to my 2006.

The car is running rich when the engine is cold. You would want the cat to come up to temp as quickly as possible to work properly...putting out less contaminants. Also, you would want a bit of back pressure in the low RPMs to help with torque. BMW would NOT go through all that trouble to just "muffed" the exhaust sounds as there are other simpler ways of doing that!

[X3eme]

Originally Posted by dkl

The car is running rich when the engine is cold. You would want the cat to come up to temp as quickly as possible to work properly...putting out less contaminants. Also, you would want a bit of back pressure in the low RPMs to help with torque. BMW would NOT go through all that trouble to just "muffed" the exhaust sounds as there are other simpler ways of doing that!

Just to play devil's advocate...



Given that sport package X3's don't have the valve at all, and have slightly wider diameter muffler tips causing even less back pressure:

1. If the closed valve is helping the cat heat up faster thereby reducing contaminates, does that mean that it is OK for sport packages to pollute more?

2. Wouldn't you expect the "sport package" to have more torque at low RPMs than the non-sport? It certainly wouldn't have less. Why don't sport packages have the valve if it provides for more torque?



Here is where my crazy hypothesis from before kicks in:

3. It might be safe to say that someone who buys a sport package vehicle would be happier with a louder, more sporty exhaust note. Perhaps leaving the valve off, but tuning the sound a little with a slightly wider opening would make it louder, but still sound like a BMW.

4. For those that do not choose to buy a sport package X3 we might assume that they want a more civilized, even luxurious driving experience. To do that we may make the muffler openings a little smaller to quiet the sound at higer RPMs. What if these smaller openings caused a wild, uncivilized exhaust note at lower RPMs? Perhaps plugging one hole up with a valve would work at these lower RPMs. We will sacrifice a little power, plugging up one hole in the muffler, but it isn't much and it will be worth it to give a more civilized, luxurious driving experience.



Sound too crazy to be true?

[rayxi]

The solenoid muffler flap is to reduce noise at low RPM. It is closed below ~4500 RPM and open open above that. I doubt it has anything to do with warming up the cats or sensors as it is controlled by RPM and not exhaust temperature.

Why is it there? It's there to pass certain noise standards at lower RPM while maintaining performance characteristics at WOT.

[The Cleaner]

Originally Posted by noncom23

So Cleaner, you have to teach now. What are the potential hazzards here. Want some input
before I do this to my 2006.

Seems harmless, but I would not know, I May be wrong about what the valve does. Someone else mentioned it was only to quiet the exhaust. I was thinking there are easier ways to quiet the exhaust but it’s very possible thats the only purpose. I have been reading the 335i has a similar valve and exhaust only exits one pipe till it warms up. I just have a feeling it’s doing more than it appears.

[[email protected]]

Originally Posted by rayxi

The solenoid muffler flap is to reduce noise at low RPM. It is closed below ~4500 RPM and open open above that. I doubt it has anything to do with warming up the cats or sensors as it is controlled by RPM and not exhaust temperature.

Why is it there? It's there to pass certain noise standards at lower RPM while maintaining performance characteristics at WOT.

My idea on this- -BMW put this in to reduce gas mileage because of heavy pressure from the big oil companies--they are concerned anytime a manfacturer comes out with a more powerful engine that gets better EPA numbers than the previous model, its bad for the oil business--so I say stick it to the oil guys--leave your valves wide open--better mileage and more noise--sounds like a win-win to me. BTW my mileage is up 5 MPG since the modification..( ). Beware of oil company investigators looking up our tailpipes. I'm afraid if too many of us do this the price of oil will rise just like the recent "Merry Christmas" rise.-So open those valves and have A Happy New Year!!

[noncom23]

Thx to all for letting me hijack here, Would love to here some more performance responses.