[Habber]

I'm not too familiar with engines but isn't there some type of protection against revving it too high?

[CanAutM3]

Originally Posted by Habber

I'm not too familiar with engines but isn't there some type of protection against revving it too high?

See post #15

[MadZarBMR]

Originally Posted by CanAutM3

See post #15

LOL you beat me to it - or post 22

Both very good.

[CanAutM3]

Originally Posted by MadZarBMR

LOL you beat me to it - or post 22

Both very good.

Post #22 does not explain that you can over-rev, meaning revving past redline, despite the limiter and without doing a money shift, which is a precision I wanted to bring. Albeit such over-revs are relatively minor (a few 100RPM at the most).

[DE Urlaub]

So, in general, I'd like to understand the "over-rev" issue as I am a 6MT owner. Is this the way the system works?:

If you are up-shifting, you would be protected by the engine's rev-limiter and theoretically if you bump up against it the engine will protect itself. If you are down-shifting and shift to too low of a gear and the engine is forced, by the laws of physics, to rev above the red line then there is a potential for damage the engine, i.e. the rotating mass is sped beyond its limits.

Thanks!

[CanAutM3]

Originally Posted by DE Urlaub

So, in general, I'd like to understand the "over-rev" issue as I am a 6MT owner. Is this the way the system works?:

If you are up-shifting, you would be protected by the engine's rev-limiter and theoretically if you bump up against it the engine will protect itself. If you are down-shifting and shift to too low of a gear and the engine is forced, by the laws of physics, to rev above the red line then there is a potential for damage the engine, i.e. the rotating mass is sped beyond its limits.

Thanks!

That's about right.

Not that a over-rev could occur when the driver wants to upshift but selects a lower gear by error (as in the Acura video previously posted).

[DE Urlaub]

Thanks. Is the rev-limiter electrical or fuel management?

Edit: Sorry - I missed the over-rev explanation at the top of the page.

[donkey]

The trick is all in how you hold the shifter when shifting, there is a way to do it to prevent money shifts

[overcoil]

Two things ( hope not repeating anything above ). But if you accidentally downshift to too low a gear, you can hear it feel it momentarily as you let up on the clutch so you immediately go and depress the clutch to recover.

Now imagine missing and engaging into to low a gear while hooning it on a motorcycle. That could flip you over the handlebars, so bikes can have slipper clutches to prevent the rear wheels from slowing too fast.

[David70]

Seems to me that the same questions keeps getting asked and answered in this post.

I also have a manual transmission and have never had a money shift, nor am I afraid it might happen tomorrow.

[GuidoK]

I wonder if you roll of a really steep mountainroad with a DCT in gear, will it shift up (in manual mode) when it sees the rpm climbing past the rev limiter?
This is ofcourse a fairly hypothetical situation....

As for the money shifts, this is obviously only possible with an interference engine (but probably all mainstream engines are nowadays)

[Falafel Combo]

[Falafel Combo]

^^^


Money shift. It seems that they mostly happen when you're trying to grab 4th gear in a hurry, but you yank on the stick shift too hard and put her in 2nd instead. Ouch!!!

[overcoil]

Originally Posted by GuidoK

I wonder if you roll of a really steep mountainroad with a DCT in gear, will it shift up (in manual mode) when it sees the rpm climbing past the rev limiter?
This is ofcourse a fairly hypothetical situation....

As for the money shifts, this is obviously only possible with an interference engine (but probably all mainstream engines are nowadays)

Are you sure fatal over rev is strictly valve contact on interference style engines?

[JsL]

This video is a classic.

[zx10guy]

Originally Posted by ScottSinger

Two things ( hope not repeating anything above ). But if you accidentally downshift to too low a gear, you can hear it feel it momentarily as you let up on the clutch so you immediately go and depress the clutch to recover.

Now imagine missing and engaging into to low a gear while hooning it on a motorcycle. That could flip you over the handlebars, so bikes can have slipper clutches to prevent the rear wheels from slowing too fast.

And as with all protection/safety devices, slipper clutches are also not 100% fool proof. I know. I was able to spin up the rear tires while downshifting too aggressively on my 2004 ZX-10R. Extremely scary moment. Only time it's happened to me on any bike with a slipper clutch. Haven't run across that problem with the S1000RRs I've used on the track. I'd be curious to see what would happen on that bike since it has a slipper clutch and also the electronics to facilitate clutchless downshifting.

[zx10guy]

Originally Posted by David70

Seems to me that the same questions keeps getting asked and answered in this post.

I also have a manual transmission and have never had a money shift, nor am I afraid it might happen tomorrow.

Me neither. My current 135i is the only auto trans car (DCT) I've owned in quite some years. I've done aggressive shifting with a range of cars from my lowly Focus to my Z28 with the T56 Borg Warner trans. When I do miss a shift, I usually feel some resistance in the shifter due to the speed miss match to the gear I was inadvertently trying to shift in to. When I feel this I know not to keep forcing the shifter into that gear.

With all the issues I've had with my DCT with the suggested fixes kicked around on this forum, I would rather have a 6 speed manual.

[boss2k]

Originally Posted by YasM3

I do not know why you would want to do that, but you can call it that because its gonna cost you some $$$$$$. That would put you roughly at 8100 RPMs

I wouldn't , trying to understand when money shifting happens.

[Arcades]

Originally Posted by zx10guy

Me neither. My current 135i is the only auto trans car (DCT) I've owned in quite some years. I've done aggressive shifting with a range of cars from my lowly Focus to my Z28 with the T56 Borg Warner trans. When I do miss a shift, I usually feel some resistance in the shifter due to the speed miss match to the gear I was inadvertently trying to shift in to. When I feel this I know not to keep forcing the shifter into that gear.

With all the issues I've had with my DCT with the suggested fixes kicked around on this forum, I would rather have a 6 speed manual.

I'm pretty certain the 135i DCT is different from the M-DCT that is on the F80s. They are several years apart so I doubt they are completely the same or behave the same way.

[GuidoK]

Originally Posted by ScottSinger

Are you sure fatal over rev is strictly valve contact on interference style engines?

on a reciprocating engine, usually yes.
Theoretically a very fast rise or fall of rpms can snap a chain or belt (more common on diesel engines though), which of course also damages the valves, but in that case you also have a broken chain/belt (least of your worries on that point )
But on classic over rev, floating of the valves is usually the first thing that happens.
Obviously when you're doing 120+mph and you manage to get the shifter in 1st, all kinds of things in the drivetrain can break too, so overrevving to 20krpm probably will give some interesting extended damage.

[eluded]

Originally Posted by GuidoK

But on classic over rev, floating of the valves is usually the first thing that happens.

Yup. Most likely the first thing that goes will be the valves followed by more expensive stuff

[Properstyle]

A money shift: when you are doing say 80mph and instead of down shifting in to 4th from 6th you go 2nd lol.....the rpms shoot up rapidly normally ending a broken valve spring, rocker arm (vehicle dependent) etc.