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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!
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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?
