[sinbad4]

I recently acquired a JB4. One of the JB4's features I liked over the Dinan is the ability to turn the exhaust bypass off and on at will (pressing BC on blinker for 2 seconds). For those of you unfamiliar with M40i exhaust, there is a bypass valve that on the left (driver) side of the car. The valve is closed at start and low RPMs.

Initially, from my reading, it seemed as though BMW utilized the bypass to add back pressure at low RPMs to increase torque. Some people suggested it would help engine heat up faster as well.

After playing with the bypass - turning it on and off for periods of time - I am of the opinion is primarily for noise control.

I have the ASD (Audio Sound Design - generation of engine noise over sound system) turned off. My car is actually pretty quiet. I can hear the burbles and pops in sport mode, but comfort, eco and adaptive are pleasantly quiet. I was a little started to hear exhaust drone in Eco mode. Almost unpleasant levels. Not bad if your driving with spirit, but possibly annoying when family or friends pleasant and just enjoying some conversation or soft music.

Having had this experience, I do not think think I would disable it - unless, like me, you have a JB4 and can turn it on an off in 2 seconds. At least consider that you will have additional noise and drone during all driving modes, not just sport.

Keep in mind. I love hearing my engine, drone, burble, pop, fart, etc! But even more I love that my X3 allows me to also drive in more civilized modes as well. Really, BMW should have added a button, like MB does, that would allow us all to open it up or quiet it down at will in any mode.

[MechX3M40i]

I wonder, for those who pulled the fuse to keep the bypass valve open at all times, would share your observation here. Maybe it was also the JB4?

X3 M40i Exhaust Mod https://x3.xbimmers.com/forums/showthread.php?t=1452260

[chicagofan00]

I prefer pulling the fuse and keeping both exhausts open at all times.

However, I am also the type that likes to drive in Sports mode 98% of the time too.

[nogren]

Wasn't there a new rule, perhaps within EU, that new cars are not allowed to add unnecessary sounds, like opening a valve in the exhaust system with a button? And the example was Porsche and MB that do a big think out of it. Perhaps if having more purpose than sounds, and doing it only in sport mode, BMW can get away with it...

[MechX3M40i]

Originally Posted by nogren

Wasn't there a new rule, perhaps within EU, that new cars are not allowed to add unnecessary sounds, like opening a valve in the exhaust system with a button? And the example was Porsche and MB that do a big think out of it. Perhaps if having more purpose than sounds, and doing it only in sport mode, BMW can get away with it...

I think the main issue is, whether the new rule is enforceable, and, if people really care to catch owners doing the mod. :

[BMWZ4]

Sorry to hijack, but quick one if you dont mind. You're obviously driving an x3 m40i (year?) and wondered how you were liking the JB4? Is it very smooth or reasonably smooth through the entire band?

[sinbad4]

Originally Posted by BMWZ4

Sorry to hijack, but quick one if you dont mind. You're obviously driving an x3 m40i (year?) and wondered how you were liking the JB4? Is it very smooth or reasonably smooth through the entire band?

It's been pretty harsh winter up here in MN - I am am running snow tires. I've mostly been in Eco mode to work. I use on setting Map #2, which is 4psi over stock. Eco mode feels the same (gutless). I switched in to sport for a tight passing situation the other day and the M40i accelerated from 72 to 102 like nothing... no drama, just smooth, hard pulling and fast. Reminded me of the acceleration of my GSXR 1000 - except with much less drama. Still shocks me that a 4200 lb SUV drives like this - faster and more nimble than almost any car pre 2010.

Also, Launch Mode was fun before.. pulls even harder - Feels like my spleen swap places with my liver. Daughters notice the difference too. I can well believe the sub 4.0 second runs I've seen posted.

So.. I really haven't pushed it - aside from a couple launches. But it does have significant and noticeably more powerful pull. Engine operation is very smooth. Really, it behaves as it ever had; but pulls much harder when you ask it to. This summer I will play with Map5.

Active dash messes with controlling from blinker stalk - accept for exhaust bypass. So if you have active dash, the bluetooth connector is a must w/ iPhone app for controlling.

[BMWZ4]

Originally Posted by sinbad4

It's been pretty harsh winter up here in MN - I am am running snow tires. I've mostly been in Eco mode to work. I use on setting Map #2, which is 4psi over stock. Eco mode feels the same (gutless). I switched in to sport for a tight passing situation the other day and the M40i accelerated from 72 to 102 like nothing... no drama, just smooth, hard pulling and fast. Reminded me of the acceleration of my GSXR 1000 - except with much less drama. Still shocks me that a 4200 lb SUV drives like this - faster and more nimble than almost any car pre 2010.

Also, Launch Mode was fun before.. pulls even harder - Feels like my spleen swap places with my liver. Daughters notice the difference too. I can well believe the sub 4.0 second runs I've seen posted.

So.. I really haven't pushed it - aside from a couple launches. But it does have significant and noticeably more powerful pull. Engine operation is very smooth. Really, it behaves as it ever had; but pulls much harder when you ask it to. This summer I will play with Map5.

Active dash messes with controlling from blinker stalk - accept for exhaust bypass. So if you have active dash, the bluetooth connector is a must w/ iPhone app for controlling.

Thanks for the analysis Sinbad, much appreciated