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Does F30 LCI 6MT auto rev match prevent overreving?

5K views 25 replies 10 participants last post by  jlbjr 
#1 ·
Online videos shows that the F80 6MT auto rev match(same be similar in LCI F30) is triggered when the shifter is engaged with the clutch still depressed(disengaged). If the matching engine rpm(per wheel speed) exceeds red line, my guess is that the mechatronics won't exceed the red line. In this case, does the dash or techcometer have a warning and/or flashing red light for an imminent money shift? If the wheel speed sensor malfunctions, hopefully the auto rev match will be disabled automatically to avoid engine damage.
 
#2 ·
Usually, fuel is cut off to the injectors to limit revs, so I would think that would be what keeps the engine from overreving. Which is another wonder of electronic throttles.
 
#3 ·
So just say the auto rev match is right at red line with the shifter engaged but clutch still depressed. Based on the wheel speed the rpm is supposed to be 200rpm(for example) above red line. If the clutch is released(engaged), there is no way to not prevent the engine rpm not to shoot pass red line by 200rpm, correct(since it is solely based on gear ratios)? This can happen when shifting from, say, 5th at 80mph to 2nd. The only possible warning is that while auto rev match, the tech probably is right at red line with the clutch still depressed, and the driver and back off with that visual cue.

It looks like fuel cut off does not help with this(fuel cut off will help on bumping the speed limiter).
 
#6 ·
Not sure. I think what you're talking about is a mechanical over rev. This happens when the momentum of the vehicle causes such a sudden increase in engine speed that the valve springs can't react fast enough to prevent the valves from getting hit by a piston.
 
#7 ·
The question is if such an over-rev event occurs, how will BMW decide if it is the fault of the driver or the fault of the mechatronics? Without auto rev match the fault of a money shift is always on the driver. Maybe the LCI owner's manual will have additional warnings about this(BMWNA/BMWAG is good at disclaimers).
 
#8 ·
Maybe it's just the way I drive my car, but I would never see a reason to go to 4th gear at 80 MPH so I don't see why the money shift would happen. Maybe I am missing something?

Do you guys downshift to 4th at 80 MPH? My car pulls like crazy in 5th at 80. I don't go to 4th unless I am under 60 MPH.. more like 50 MPH.
 
#16 · (Edited)
Maybe it's just the way I drive my car, but I would never see a reason to go to 4th gear at 80 MPH so I don't see why the money shift would happen. Maybe I am missing something?
On rare occasions I've been in the midst of a freeway pass when, while observing closing rates (my own and those of cars in adjacent lanes), I've realized that a decision point has arrived: Apply more thrust to complete the pass safely without cutting too close to anyone, or abort the maneuver entirely. In New Jersey's dense but fast traffic this happens more often than you might expect, but the "more thrust" option always has to be balanced against behaving like an ass.

Do you guys downshift to 4th at 80 MPH? My car pulls like crazy in 5th at 80. I don't go to 4th unless I am under 60 MPH.. more like 50 MPH.
Try downshifting to third at 80 and put your foot flat to the floor, someday. You might revise that statement. ;)
 
#17 · (Edited)
An over-rev condition is mechanical....it cannot be prevented.

Fuel cut off does nothing.....the crank will still be driven by the wheels. Hitting/bouncing off a rev limiter is a software thing.

Even if you did get a warning, 99% of the time, you would not have enough time to take the car out of gear.

The only way I can see a safety being implemented is if the clutch line has a control valve on it. If the vehicle speed does not match the engine speed, it could basically lock the line and prevent the clutch from engaging and thus preventing the wheels from driving the crank.
 
#23 ·
It is a fair point that experienced drivers only take a split second to complete the shift, it probably is quite difficult to abort in the middle of that split second(regardless of roaring engine or grinding synchros).

Some GM cars do have skip shift on their MT to force shifting from 1st to 4th(to improve fuel efficiency and avoid gas guzzler), so maybe the solenoid mechanisms can be re-configured to prevent 5th to 2nd(for example).
 
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