Overreving engine with automatic transmition
 

Hi guys,

I've an automatic 20' BRZ (heavy traffic area, don't hate :)).
I usually drive in manual mode and was wondering if it's possible to overrev the engine with automatic transmition.

e.g, i usually downshift at 4k RPM and i get to around 6k rpm when need some power.
What will happen if i downshift at 6k, will the transmition allow it?

Thanks

Most autos with a "manual" function have a bunch of nannies that won't let your shift up or down if your outside of the rev range.

In one instance I did manage to downshift directly into the rev limiter. I have OFT as that is likely different than stock. it has never let me do it beyond that one instance, normally it leaves a cushion of some sort

OFT has a "soft rev limiter" formed by reducing timing to negative values in the top 200rpm or so. The actual "redline" is higher than the engine can achieve in gear because of this. You probably got it right in that range where the transmission saw it was ok, but the timing was reduced.

The transmission does not stop you from down shifting. The rev limiter will cut the throttle if you exceed redline over ~7500 rpm. Manual mode of AT is just "manual" in this car with a very useful rev match. There is just no clutch. I never downshifted directly to a rev above redline though. It is a good thing if AT stops that from happening instead of letting the rev limiter cutting the throttle right after downshift.

That is good to know and have. Thanks!

I drive in manual mode a good bit. You can downshift pretty much at any point. As mentioned, it's the REV Limiter that keeps you from exceeding redline, not the transmission.

The only time I've seen the transmission do anything "automatic" in manual mode is downshift if you are going slow enough the engine would stall otherwise.

On the other end, you can bounce off the rev limiter to your hearts content as far as i can tell from practical experience.

I understood the question to be whether the AT would let you money shift.

In my experience, it will not. Although technically it may let you shift down but at the same time the REV limiter keeps it left of red. I really haven't done it close enough in a while to know for sure.

I suppose never say never, there may be some magic combination of shifting, throttling, left nostril twitching all at the same time that could get past the nannies.

It won’t let you money shift. It also wont skip over gears similar to sequential.

If shifting to a gear would put you above 7400rpm rev limiter it won’t let you shift to the new gear. You can shift into a gear if when shifting it will end up at 7399rpm in the new gear and then immediately bang off limiter if you give it any gas. It also won’t let you up shift into a gear if it will drop RPM too low in the new gear IE 700rpm in 2nd won’t let you shift to 3rd.

It seems like this was answered already by @86TOYO2k17 but just for extreme clarity, money shifting is the act of accidentally downshifting instead of upshifting, and when this happens, the engine is pulled by the car's momentum and gearing into rpms that exceeds the rev limiter, whether your foot is on the accelerator or not. For instance, if someone took their car to redline in third gear, and instead of upshifting into fourth gear (dropping rpms), they accidentally downshifted back to second gear (raising the rpms).

https://i.imgur.com/O1611eq.jpg

If we use this chart, and the example I gave, then we see that in third gear at redline we would be traveling around 95mph. If we shifted into second gear by accident then we would still be close to 95mph, and the rpms would be around 10,500rpms.

Even worse, if the rev limiter cuts the throttle at the same time when the engine is forced to rev at 10500rpm, there can be engine damage until engine brake slows the car down and rpm decrease below red line. I would imagine that is a big impact load on valvetrain and connecting rods. I have done accidental downshifts before and the AT allowed those. Since the shifting mechanism is sequential, one has to do a triple tap for such a severe case. I think the AT will not do that downshift, but I have no intention to find out.

Not multiple. Downshift at redline by hitting the wrong paddle in an automatic that doesn't lock you out of gear is all it takes. Hit the rev limiter in this situation is good, so the accelerator wouldn't cause even more revs.


Yes, this is bad on the connecting rods and on the valvetrain, specifically for valve float.

That face when you downshift and send the revs to the moon.

"But muh rev limiter...."


https://www.zx6r.com/attachments/201...204-jpg.94874/

https://www.zx6r.com/attachments/201...241-jpg.94876/

https://www.zx6r.com/attachments/201...216-jpg.95010/