Only the left exhaust pipe seems to be working?

sbc-yyc · 11-21-2022, 10:14 AM

Hi all,

The 40i has two exhaust pipes as you may know, but of late I've seen exhaust fumes coming out of left pipe only. Doesn't matter if I've just started the car or I've been driving it for a few hours, I'm seeing vapour and condensation etc. coming out of the left pipe. Did not notice this behaviour in the summer, but it's extremely evident in colder temperatures now. After a relatively long drive of around 60 kms, I touched the tip of the right exhaust and it was absolutely cold. The temperature gauge was right where it is supposed to be when the engine is sufficiently warmed up.

Is this expected behaviour? Do both exhaust pipes become operational when the engine gets really hot? Or is something wrong with the exhaust on my X5? I can post pictures if needed. There are no warning messages, no errors etc., anywhere that I can see. Nothing wrong with the way the car drives either. Everything is hunky dory so I'm a bit befuddled.

Any pointers? Thanks & Cheers!

finn123 · 11-21-2022, 10:16 AM

Hi,

There is an exhaust flap on the right exhaust pipe, which opens after ~3000-3500 rpm

sbc-yyc · 11-21-2022, 12:53 PM

Quote:

Originally Posted by finn123

Hi,

There is an exhaust flap on the right exhaust pipe, which opens after ~3000-3500 rpm

Thanks! Does that mean the right exhaust never really works unless I rev the engine beyond 3000 rpm? It doesn't have anything to do with the temperature of the engine?

And what about sports mode? If I switch the drive mode to sports(plus/individual) doesn't the flap open in that case?

eelnoraa · 11-21-2022, 01:32 PM

I don’t think it has anything to do with engine temp. It has to do with the exhaust gas velocity. At low rpm, flow volume is low, so one side is close to keep the rate of the flow “speed” high, lower pressure, actual help exhaust better. Engine gets better low end torque. Not sure if ever notice when people mod exhaust with mindless large pipe, they actually go slower. This is the reason. I think this mechanism is called exhaust scavenging, but I could be wrong with naming convention.

Having this said, I notice on my older bmws actually has this flap open in idle, so it give a louder sound. It closes when the car get moving until 3000ish rpm, the open again.

jad03060 · 11-21-2022, 03:45 PM

Exhaust gas velocity is integral to spinning the turbo, so closing one off at lower RPM means boost sooner. AT higher RPM, too much back pressure will then also affect the velocity, cutting turbo boost, so to even things out across a wider RPM range, they added the flap.

eelnoraa · 11-21-2022, 04:47 PM

Quote:

Originally Posted by jad03060

Exhaust gas velocity is integral to spinning the turbo, so closing one off at lower RPM means boost sooner. AT higher RPM, too much back pressure will then also affect the velocity, cutting turbo boost, so to even things out across a wider RPM range, they added the flap.

Oh, this is actually a good point too. It is probably even more important for turbo engine, could be one of the contribution to such a good low end torque of modern low boost turbo design.

Just want to shre, the 1 pipe closing scheme was in very early non turbo as well, like S62 V8, M54 Inline6.

sbc-yyc · 11-22-2022, 12:47 AM

Wow. That's an amazing piece of information. Thanks all for sharing. I rest easy now, knowing it's all working as designed.

Qsilver7 · 11-22-2022, 02:54 PM

here's some info about the exhaust flap

MaKSiNG · 11-22-2022, 06:03 PM

So it looks like the use of this flap in the left ‘zorst is common across the different models.
The X3 guys and gals talk about removing the fuse to the flap actuator in order for the flap to remain open all the time, thereby having both exhausts functional at all times. Mostly to increase noise, particularly on startup.

11-21-2022, 10:14 AM	#1
sbc-yyc Private First Class 87 Rep 100 Posts Drives: 2021 X5, 2018 Q5, 2018 P100D Join Date: Jul 2022 Location: Calgary iTrader: (0)	Only the left exhaust pipe seems to be working? Hi all, The 40i has two exhaust pipes as you may know, but of late I've seen exhaust fumes coming out of left pipe only. Doesn't matter if I've just started the car or I've been driving it for a few hours, I'm seeing vapour and condensation etc. coming out of the left pipe. Did not notice this behaviour in the summer, but it's extremely evident in colder temperatures now. After a relatively long drive of around 60 kms, I touched the tip of the right exhaust and it was absolutely cold. The temperature gauge was right where it is supposed to be when the engine is sufficiently warmed up. Is this expected behaviour? Do both exhaust pipes become operational when the engine gets really hot? Or is something wrong with the exhaust on my X5? I can post pictures if needed. There are no warning messages, no errors etc., anywhere that I can see. Nothing wrong with the way the car drives either. Everything is hunky dory so I'm a bit befuddled. Any pointers? Thanks & Cheers! __________________ 2021 BMW G05 X5 xDrive40i - Tanzanite Blue/Coffee Merino - 11/2023.50 2018 Audi Q5 45 TFSI - Ibis White 2018 Tesla Model S P100D - Midnight Silver
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11-21-2022, 10:16 AM	#2
finn123 Second Lieutenant 159 Rep 272 Posts Drives: - Join Date: Mar 2018 Location: - iTrader: (0)	Hi, There is an exhaust flap on the right exhaust pipe, which opens after ~3000-3500 rpm
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11-21-2022, 01:32 PM	#4
eelnoraa Brigadier General 2060 Rep 3,708 Posts Drives: G05 X5 Join Date: May 2022 Location: SF Bay Area CA iTrader: (0)	I don’t think it has anything to do with engine temp. It has to do with the exhaust gas velocity. At low rpm, flow volume is low, so one side is close to keep the rate of the flow “speed” high, lower pressure, actual help exhaust better. Engine gets better low end torque. Not sure if ever notice when people mod exhaust with mindless large pipe, they actually go slower. This is the reason. I think this mechanism is called exhaust scavenging, but I could be wrong with naming convention. Having this said, I notice on my older bmws actually has this flap open in idle, so it give a louder sound. It closes when the car get moving until 3000ish rpm, the open again. __________________ 2022 G05 B58/PHEV + a few very old BMWs
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11-21-2022, 03:45 PM	#5
jad03060 Major General 3214 Rep 6,885 Posts Drives: X5 45e Join Date: Aug 2018 Location: NH iTrader: (0)	Exhaust gas velocity is integral to spinning the turbo, so closing one off at lower RPM means boost sooner. AT higher RPM, too much back pressure will then also affect the velocity, cutting turbo boost, so to even things out across a wider RPM range, they added the flap.
	Appreciate 2 sbc-yyc86.50 MJBradley1967196.50 Quote

11-22-2022, 12:47 AM	#7
sbc-yyc Private First Class 87 Rep 100 Posts Drives: 2021 X5, 2018 Q5, 2018 P100D Join Date: Jul 2022 Location: Calgary iTrader: (0)	Wow. That's an amazing piece of information. Thanks all for sharing. I rest easy now, knowing it's all working as designed. __________________ 2021 BMW G05 X5 xDrive40i - Tanzanite Blue/Coffee Merino - 11/2023.50 2018 Audi Q5 45 TFSI - Ibis White 2018 Tesla Model S P100D - Midnight Silver
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11-22-2022, 02:54 PM	#8
Qsilver7 Major General 4504 Rep 7,548 Posts Drives: F06 650ix GC / F15 X5 50i Join Date: Oct 2016 Location: Indiana, USA iTrader: (0)	here's some info about the exhaust flap Attached Images __________________ 2015 F06 650ix Gran Coupe`(Moonstone/Cohiba Brown)\| 2014 F15 X5 50i MSport (Space Gray/Mocha) Become a BMW CCA member! Click HERE to join and feel free to use my BMW CCA member #191509 as a referral.
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11-22-2022, 06:03 PM	#9
MaKSiNG Private 20 Rep 84 Posts Drives: 2019 X5 40i MSport Join Date: Oct 2012 Location: Pennsylvania iTrader: (0)	So it looks like the use of this flap in the left ‘zorst is common across the different models. The X3 guys and gals talk about removing the fuse to the flap actuator in order for the flap to remain open all the time, thereby having both exhausts functional at all times. Mostly to increase noise, particularly on startup.
	Appreciate 0 Quote