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      07-07-2013, 10:55 PM   #1
pocoyo_3
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N55 Revs Hanging

I just picked up a 2011 335i. One aspect that I do find bothersome is that the revs hang when I downshift, and this is particularly annoying when coming down the gears from 3rd to 2nd, for example.

Is this behaviour normal, or is there a software update that my car requires? Is anyone aware if the performance pack improves this?

Thanks in advance.
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      07-07-2013, 11:00 PM   #2
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When the clutch is pressed in, you'd expect the revs to drop, they don't in these cars ...I have noticed the same with my 2011 335i. I've dismissed the behavior as something intentional - and have just become used to it. This isn't a car you can just bang through the gears. I find myself shifting late in other manual cars.

I think it's called "rev hang" ...a lot of cars have it. On other cars it can be fixed via software. I have not researched possible fixes for our cars.
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      07-08-2013, 12:54 AM   #3
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Even in my 2011 335 when I go through sport mode shifting the revs hang when I downshift. It's okay...not a terrible thing.
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      07-08-2013, 02:50 AM   #4
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It's due to the super heavy flywheel
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      07-08-2013, 08:46 AM   #5
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Thanks everyone. For me this kills the driving experience. My reference was my previous N52 325i, and that engine just felt that much more natural to me.
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      07-08-2013, 03:13 PM   #6
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Quote:
Originally Posted by my325i View Post
Thanks everyone. For me this kills the driving experience. My reference was my previous N52 325i, and that engine just felt that much more natural to me.
Agreed, the N52 shifts as it should. You could probably fix our issues with a lighter flywheel as noted, though I have not seen any N55 guys do that. You might want to ask in the N54 section.
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      07-08-2013, 03:25 PM   #7
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Quote:
Originally Posted by CJ421 View Post
Agreed, the N52 shifts as it should. You could probably fix our issues with a lighter flywheel as noted, though I have not seen any N55 guys do that. You might want to ask in the N54 section.
Well the reason I haven't swapped (and I believe everyone else as well) is because N55 cars are more likely to still be under warranty than the N54 cars. Swapping the flywheel would void the clutch assembly's warranty (and maybe the whole transmission) so it's definitely not worth it. If you eventually upgrade to the big turbo kit you will have to replace the clutch to handle the extra power and you might as well do the flywheel while you're at it. That's my plan, anyway
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      07-08-2013, 04:53 PM   #8
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I'm not sure if it's the physical weight of the flywheel, or if it's the throttle mapping and electronics which contribute to the revs hanging.
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      07-08-2013, 05:12 PM   #9
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My AT does it too...annoying as shit, but now at least it looks like it's normal
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      07-08-2013, 10:59 PM   #10
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Quote:
Originally Posted by my325i View Post
I'm not sure if it's the physical weight of the flywheel, or if it's the throttle mapping and electronics which contribute to the revs hanging.
It definitely feels like the flywheel, which is why if you are coasting for a few seconds (off the gas) and then put the clutch in, the revs fall quickly. If you were just on the gas it takes the flywheel a second to lose momentum and slow down, this causes the rev hang. You'll also notice revs hang worse at higher RPM. The heavy flywheel is also what ruins throttle response for rev matching, since it takes so much gas to get that heavy POS going. I sort of have to "stab" the throttle to the floor for a fraction of a second for 2->3 or 2->1
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      07-09-2013, 12:54 AM   #11
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Quote:
Originally Posted by hetzle View Post
It definitely feels like the flywheel, which is why if you are coasting for a few seconds (off the gas) and then put the clutch in, the revs fall quickly. If you were just on the gas it takes the flywheel a second to lose momentum and slow down, this causes the rev hang. You'll also notice revs hang worse at higher RPM. The heavy flywheel is also what ruins throttle response for rev matching, since it takes so much gas to get that heavy POS going. I sort of have to "stab" the throttle to the floor for a fraction of a second for 2->3 or 2->1
I always thought it was because of the delay due to the drive-by-wire not the actual flywheel itself. Maybe you're right
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      07-09-2013, 01:12 AM   #12
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Quote:
Originally Posted by rr006rbc View Post
I always thought it was because of the delay due to the drive-by-wire not the actual flywheel itself. Maybe you're right
It could be a combination of the two, my old E36 M3 had a 11.5lbs flywheel (super light) and the switch to an E39 M5 with a 39.7 lbs made me realize what a difference it makes. This car definitely has a heavy dual mass flywheel, I'm not sure of the exact weight though
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      07-09-2013, 08:42 AM   #13
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It is also part of the ECU programming for emissions reduction. My Acura had it to on my 6MT and I hated waiting for the engine to slow down to engage the clutch. A lighter flywheel won't eliminate this.
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      07-09-2013, 12:24 PM   #14
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a way around this is to drive in M mode vs. DS or D...........
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      07-09-2013, 01:27 PM   #15
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Quote:
Originally Posted by Ml3456 View Post
It is also part of the ECU programming for emissions reduction. My Acura had it to on my 6MT and I hated waiting for the engine to slow down to engage the clutch. A lighter flywheel won't eliminate this.
Are you sure that we have the same ECU programming or is this just a guess? If so, we could possibly tune that out.

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Originally Posted by madmanhiker View Post
a way around this is to drive in M mode vs. DS or D...........
That requires having an automatic
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      07-09-2013, 01:39 PM   #16
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^ sorry... missed that. jeez, he is having rev hang in a manual??? that does suck.
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      07-09-2013, 02:41 PM   #17
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Quote:
Originally Posted by madmanhiker View Post
^ sorry... missed that. jeez, he is having rev hang in a manual??? that does suck.
We all are, but it's not nearly as slow as the auto versions of these cars, I can definitely downshift way faster than the auto tranny but the revs tend to hang a bit when you put the clutch in. I'm 99% sure it's caused by a heavy flywheel
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      07-09-2013, 03:49 PM   #18
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I'm going to agree about the heavy flywheel. Rev-matched downshifting requires a healthy stab of the accelerator to get the revs up.
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