Over Rev Protection
Thread Starter
Heel & Toe
Joined: Jan 2009
Posts: 19
Likes: 2
From: California
Over Rev Protection
I'm a die-heard "self-shifter" and admit to an over rev situation on previous models a few times. My error and fortunately no foul as the computer did it's job and protected the car.
I have a question regarding how the auto trans handles such situations. Will the computer not allow over revs even when shifted with the paddles? How about an unintended paddle downshift causing a serious over rev?
I have a question regarding how the auto trans handles such situations. Will the computer not allow over revs even when shifted with the paddles? How about an unintended paddle downshift causing a serious over rev?
Safety Car
Joined: Aug 2012
Posts: 3,960
Likes: 1,106
The computer will protect against over rev both by limiting engine speed in a gear and denying a shift to a gear which would result in either excess engine speed or insufficient speed/torque capability for the requested gear. If you try to shift up or down into an inappropriate gear you will get a "shift denied" message.
The only case where you might be able to exceed the safe engine RPM would be to select a low gear on a steep grade and not use any braking. If the incline is sufficient I suspect the controller would allow the engine to go to excessive RPM rather than force an upshift when in manual mode. This is one experiment I will not be conducting.
The only case where you might be able to exceed the safe engine RPM would be to select a low gear on a steep grade and not use any braking. If the incline is sufficient I suspect the controller would allow the engine to go to excessive RPM rather than force an upshift when in manual mode. This is one experiment I will not be conducting.
Last edited by NSC5; Jul 23, 2017 at 09:57 AM.
Tech Contributor
Joined: Oct 1999
Posts: 41,037
Likes: 9,801
From: Charlotte, NC (formerly Endicott, NY)
If the A8 is in manual mode why isn't the driver a self shifter? The driver can choose the gear and how long they want to be in it other than the protections to prevent engine or car damage that are impossible to implement with a manual transmission. It only takes one missed downshift from 5th to 2nd instead of 5th to 4th with the M7 to put a car violently into a wall on the track let alone blow the engine.
Bill
Bill
Safety Car
Joined: Sep 2015
Posts: 4,785
Likes: 1,417
You most definitely can mechanicaly over rev the engine with the M7. No computer can save you from being ham fisted, that that's just engineering.
Otoh, an automatic trans, (not really shifting), simply will not let you hurt the engine by downshifting. It simply will not shift until it's ok to do so. And most of the time it shifts when it want to, not necessarily when the driver asks it to.
Otoh, an automatic trans, (not really shifting), simply will not let you hurt the engine by downshifting. It simply will not shift until it's ok to do so. And most of the time it shifts when it want to, not necessarily when the driver asks it to.
Heel & Toe
Joined: Jun 2017
Posts: 22
Likes: 5
You cannot over rev while accelerating as the computer will cut fuel at redline. If you are accelerating and at 95 mph in third and try to go to fourth and accidentally put it in second, prepare for your valves to float with an awful smacking sound of pistons when you let the clutch out. There is no way the computer can cut off the manual connection between wheel speed and the engine RPMs in a M7 when in gear and not on the clutch.
Note, the auto rev match will not over-rev your engine. If you go from third to second in the same scenario but don't let off the clutch, there won't be any damage. I think it rev matches up to 5500 RPM.
Note, the auto rev match will not over-rev your engine. If you go from third to second in the same scenario but don't let off the clutch, there won't be any damage. I think it rev matches up to 5500 RPM.
Safety Car
Joined: Aug 2012
Posts: 3,960
Likes: 1,106
And to add to what Glenn said if you are paying attention when you attempt to accidentally shift into a lower gear you will hear the synchros screaming and that is your clue NOT to let off the clutch.
If we continue to try to idiot proof cars I expect some manufacturer will add a lockout solenoid to prevent the clutch pedal from returning if an incorrect lower gear is selected during a shift. Of course this brings up the interesting safety/liability concern for the rare case where someone would prefer to purposely "blow" the engine in an attempt to slow the car but I don't think there are many cases where a car speeding out of control due to a loss of brakes will be better off spinning out of control due to suddenly locked rear wheels from a highly oversped and now seized engine
If we continue to try to idiot proof cars I expect some manufacturer will add a lockout solenoid to prevent the clutch pedal from returning if an incorrect lower gear is selected during a shift. Of course this brings up the interesting safety/liability concern for the rare case where someone would prefer to purposely "blow" the engine in an attempt to slow the car but I don't think there are many cases where a car speeding out of control due to a loss of brakes will be better off spinning out of control due to suddenly locked rear wheels from a highly oversped and now seized engine
Last edited by NSC5; Jul 25, 2017 at 06:11 PM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
Pro
Joined: Apr 2012
Posts: 642
Likes: 11
From: Reno, NV
I’m pretty sure the car applies its rear brakes if the operator shifts to a gear that would cause the engine to over speed by being driven by the rear wheels. The rear brakes apply just enough to prevent engine over speed and fuel cut-off is also activated. I assume this as I have made bad downshifts twice and both times the engine did not over speed but the rear wheels did drag. If the driver doesn’t correct the gaff the car’s rear fishtails a fair amount until the clutch is disengaged or speed otherwise meets spec. I think this feature was introduced in 2006 but I could be wrong.
Tech Contributor
Joined: Oct 1999
Posts: 41,037
Likes: 9,801
From: Charlotte, NC (formerly Endicott, NY)
I’m pretty sure the car applies its rear brakes if the operator shifts to a gear that would cause the engine to over speed by being driven by the rear wheels. The rear brakes apply just enough to prevent engine over speed and fuel cut-off is also activated. I assume this as I have made bad downshifts twice and both times the engine did not over speed but the rear wheels did drag. If the driver doesn’t correct the gaff the car’s rear fishtails a fair amount until the clutch is disengaged or speed otherwise meets spec. I think this feature was introduced in 2006 but I could be wrong.
Bill