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Does the C8 DCT have anything that keeps you from down shifting at too high of RPM’s? I know it’s sequential but, what if you are at redline and downshift instead of up shift or downshift 2-3 times and not slowing fast enough? Is there anything that keeps you from mechanically over reving the engine? Just a question I have not found an answer to. Thanks!
The Manual Paddle Shift system will
not allow an upshift or a downshift if
vehicle speed is too fast or too slow,
nor will it allow a start from any gear
other than 1 (First) gear.
That’s what I would have thought, but couldn’t find it written anywhere! Someone said it has a rev-limiter but that has nothing to do with mechanical over-rev.
thanks
What prevents the mechanical over-rev is the software that will not allow the shift to occur if it would over rev the engine as stated above. In a normal manual shift car you could make it mechanically over rev by being in 3rd gear (as an example) at near redline and shifting down into 2nd rather than an upshift into 4th.
This had to be pointed out to BMW on the E46 M3s with the SMG transmission, an early electro-hydraulic shift manual transmission after the dealers tried to stiff owners when the engine computer showed several blown engines had all been rev'd to a precise number, something like 9368 RPM. Those SMG transmissions also had programing that would reject a downshift if it would over rev the engine. Subsequently BMW did a recall and replaced the engine bearings and then specified Castrol 10W-60 oil to be used in those engines. Our E46 M3 worked fine for the 60K miles that we had it, including a few track days using it to take students around.
Last edited by AzDave47; May 17, 2025 at 08:29 PM.
That’s what I would have thought, but couldn’t find it written anywhere! Someone said it has a rev-limiter but that has nothing to do with mechanical over-rev.
thanks
Its in the Owner's Manual. There are even tables that give you the Maximum Downshift Inhibit Speeds into each gear for the Z51, non Z51, and Z06.
It says this:"To prevent damage to the powertrain, Manual Paddle downshifts cannot be performed above certain speeds. The vehicle speeds for allowed Manual Paddle shifts can vary by vehicle model or optional equipment; such as the Stingray Z51 with Electronic Limited-Slip Differential (eLSD) differs from non-Z51 with Mechanical Limited-Slip Differential (mLSD)." And then it provides several pages of tables showing those speeds for each model. There are also minimum upshift speeds listed - to prevent lugging.
Not sure what you intend by "mechanical". There are sensors that measure RPM and vehicle speed, but its all software controls that allow or inhibit gear changes. It is also software that limits RPM at or near redline.
A rev limiter has nothing to
do with a mechanical over rev.
If you are in a manual trans at 6500 rpm in 3rd gear and accidentally shift to 2nd instead of 4th, the rpm will probably go to 9000. No rev limiter in the ECM is stopping that.
Modern DCTs prevent that mechanical over rev from happening in the first place by not allowing that accidental shift to 2nd (when you meant to shift to 4th) but it isn't a rev limiter, it is the ECM deciding to not allow the shift.
Not to be confused with the Maximum Downshift Inhibit function, the so called "rev limiter" is called Engine Overspeed Protection in the version of the Service Manual that I have. It works by invoking the "Fuel Cutoff Mode". There are other conditions that will also invoke the fuel cutoff mode, such as extended, closed throttle coasting. As noted now in several posts, the function that prevents engine over-revving caused by downshifting to a gear too low for the speed of the car is called Maximum Downshift Inhibit, which is described in the Owner's Manual along with the speeds above which a downshift into a particular gear will be prevented.
Both features are implemented in software using sensors for the relevant parameters, one by invoking the fuel cutoff mode, the other by inhibiting the requested downshift (or in automatic mode by not requesting a gear that is too low).
Lol....yes so matter what anyone or GM calls it, that is a rev limiter whether over revving on up rev or downshifting improperly. Normally when hitting it you get a banging affect.
Jack, perhaps with paddles and a C7 automatic BUT could not stop it in a manual C7! Yep the automatic Rev Match was computer controlled BUT if at Redline in 3rd and shifting quickly to 4th, IF you happened to pull the shift lever toward yourself as you pulled back, it would go into 2nd! It was all mechanical and there was NO blocking the 3rd to 2nd shift!
SIDEBAR
In fact they used Hall position sensors to estimate what gate you were going into to set the Rev Match rpm. They worked even in the neutral gate. I had to stop using an old method I had employed for many years when going to skip a gear downshifting. If, as often in my C7, I was going from 5th gear (which was my cruising gear in our rural area) before turning and downshifted to 3rd where I wanted to be after the turn I would often first put the car in 4th. Would do that with the clutch remaining disengaged. That spools up the cluster gears. But found with automatic rev matching it confused the system. Gave it up and just downshifted from 5th directly to 3rd. That was a common downshift as I approached a turn.
Not for manual transmission Corvettes. If you're going 80 and downshift to 2nd gear you're going to overrev the engine no matter what rev limiter the car has.
The C8 won't let you downshift to a gear that would over rev the engine.
Originally Posted by gliot1
Lol....yes so matter what anyone or GM calls it, that is a rev limiter whether over revving on up rev or downshifting improperly. Normally when hitting it you get a banging affect.
It sounds like you don't understand how manual transmissions work. No software can prevent an overrev if you downshift into too low a gear.
You can't Manually over rev/ down shift the car cause it's not a Manual transmission.... you can select a gear you want IF and ONLY IF you are with-in the set parameters programed.. which keeps you under the redline of the motor.
as for the other guys saying it has a revlimiter. the rev limitr/ spark and fuel cuts keep a Engine from spinning its self to high... it will not do anything for something else spinning it too high.... like a grabbing second gear instead of 4th in a 6/7speed.
Mechanical Over-rev?
Been a feature on the Corvette for quite a while.
