Spirited driving fail? Over rev?

[churchx]

With exception to DSG likes .. technically there are clutches. Well, non MT anyway.

[humfrz]

Originally Posted by Pepper86

I was trying to exit the freeway with "authority" and go from 6th to 4th at 70~ish. When I did so: to my surprise; it felt like I hit the brakes glanced down and saw 7k+ rpm I think it was around 7100-7200rpm but I for sure hit the rev limiter as it felt like I hit the brakes, and the engine cut out. I am sure I clutched as it is an instinct. Granted all of these event happened in a matter of seconds(or less). I am an experienced driver with some track time, so I have a decent understanding of this. I swear I went to 4th, but it is impossible for the car to hit 7500rpm in forth at any where less than 100mph if I am not mistaken. So the only other option is that I went into 2nd? Which means that I over revved? I have the Toyota 86 now which has the slightly higher final drive of 4.3~ and @70mph~ in 2nd gear is around 8500-9k(rpm)? That sound about right? I am trying to figure all of this out as like I said this all happened really fast.

I figure you got ...... lucky ......

I'd suggest you not do that too many times ......


humfrz

[Pepper86]

Originally Posted by humfrz

I figure you got ...... lucky ......

I'd suggest you not do that too many times ......


humfrz

After getting in the car this morning on my way to work I was practicing going from 6th to 4th and I for sure went to second gear last night. So I probably "zinged" the motor from anywhere around 8.5k-9k(rpm )
No warning lights atm thank God.

[TommyW]

Originally Posted by Detroiter

The limiter does help you on downshifts. In events like this when the engine hits red line the fuel cut rev limit is so harsh that it has a great chance of locking up the rear wheels. This will stop your engine from being forced to rev higher as the wheels won't be spinning any faster than it is. I've seen it happen on many different rwd cars. Never being on that I was driving I should add

That would be highly unlikely. Even if that was the case (very rare at best) the limiter would have nothing to do with it. The best way to avoid these scenarios is to practice this downshift at lower revs and let the clutch out slower in case of hitting second. Do it for awhile until you consistently have a 100% success rate and are confident hitting it right ALL THE TIME. At that point start implementing the shift at higher and higher limits. The consequences can be catastrophic.

[Detroiter]

Originally Posted by TommyW

That would be highly unlikely. Even if that was the case (very rare at best) the limiter would have nothing to do with it. The best way to avoid these scenarios is to practice this downshift at lower revs and let the clutch out slower in case of hitting second. Do it for awhile until you consistently have a 100% success rate and are confident hitting it right ALL THE TIME. At that point start implementing the shift at higher and higher limits. The consequences can be catastrophic.

Why would the limiter have nothing to do with it? It is literally only there to limit the RPM's. Downshift into wrong gear, Let of clutch which doesn't grab instantly(it's fast but not instant), engine is brought up to the RPM needed for the gear but the rev limiter tries to stop the engine from going bast the point resulting in very harsh engine braking. Then it's a fight for what gives first either the engine pushing past the fuel cut or the rear tires giving up traction. Especially on a cold day with summer tires the sudden onset of resistance could make the tires break loose.

Also I want to stress that I have NEVER done this I rev match and heel toe downshift every time I drive therefore I am very aware of how much rpm change happens between each gearing and know how it feels going into each gear. If you meant that towards OP or others then yes making sure you know the shifter and gearing is very important before downshifting.

[reeves]

Originally Posted by Sportsguy83

I have to disagree with you on this one. A long time ago when I was younger and stupid, I was racing and shifted into 2nd while trying to shift to 4th, and completely trashed an engine, pistons melted, rods broke, all kinds of shit because there was no rev limiter in the world that stopped the engine from revving to 10K+.

I was in the car with two different friends TWICE when this happened. Once in a '96 Integra (downshifted from 5th to 1st when he meant to go into 3rd gear.. at 75mph), one of the rods tore a hole right through the side of the engine.

Several years later in a '06 Civic Si, my cousin was doing 0-60 pulls and mis-shifted from 2nd to 3rd (he shifted back into 1st gear) at redline... He needed a new engine after that. I still give him a hard time about it now because the car was brand new at the time, less than 2K miles.

I would hope they've figured out a way to prevent that from happening to cars nowadays (electronically or mechanically limiting the engine revs), but can't say for sure since I haven't mis-shifted when downshifting on my BRZ yet.

[Sportsguy83]

Originally Posted by reeves

I was in the car with two different friends TWICE when this happened. Once in a '96 Integra (downshifted from 5th to 1st when he meant to go into 3rd gear.. at 75mph), one of the rods tore a hole right through the side of the engine.

Several years later in a '06 Civic Si, my cousin was doing 0-60 pulls and mis-shifted from 2nd to 3rd (he shifted back into 1st gear) at redline... He needed a new engine after that. I still give him a hard time about it now because the car was brand new at the time, less than 2K miles.

I would hope they've figured out a way to prevent that from happening to cars nowadays (electronically or mechanically limiting the engine revs), but can't say for sure since I haven't mis-shifted when downshifting on my BRZ yet.

Brings back horrible a the time, but funny today memories

[TommyW]

Originally Posted by Detroiter

Why would the limiter have nothing to do with it? It is literally only there to limit the RPM's. .

It limits RPM on acceleration but not on deceleration. You're can literally FORCE the motor into an over rev situation with a bad downshift

[Detroiter]

Originally Posted by TommyW

It limits RPM on acceleration but not on deceleration. You're can literally FORCE the motor into an over rev situation with a bad downshift

I get what you are saying, but it limits RPM period do you have any proof it will not limit it during decel? I doubt it does anything but monitor the RPM and cut fuel if they hit the specified level. If you read my last post I said it will either be the engine or the tires giving way. If it's the engine yes it will FORCE it into over reving. What I'm saying is no matter what the rev limiter will still be in effect cutting trying to stop the over rev.

[stevesnj]

Originally Posted by Detroiter

No our clutch is hydralic. I'm pretty sure there is no cars using a clutch drive by wire system, or at least I've never heard of one before.

If a dual clutch trans qualifies i'd say this is a drive by wire system with dry clutches, though there are wet clutch dual clutch systems also I believe.

[Pepper86]

Originally Posted by Detroiter

I get what you are saying, but it limits RPM period do you have any proof it will not limit it during decel? I doubt it does anything but monitor the RPM and cut fuel if they hit the specified level. If you read my last post I said it will either be the engine or the tires giving way. If it's the engine yes it will FORCE it into over reving. What I'm saying is no matter what the rev limiter will still be in effect cutting trying to stop the over rev.

It is a mechanical issue. There are no electronics that can save you from a mechanical over rev. The wheel speed will force the motor to exceed any limiter/limits. I.e. 2nd gear at ~70(mph) is roughly ~9k(rpm). Think about it like jumping out of a moving vehicle. If you jump out of a moving vehicle at 15mph you are either going to instantly run 15mph or eat it. The same with the motor. It is either going to rev to the rpm due to wheel speed or something is going to let go/give. Everything seems to be held together still, however I am worried of any scaring to a bearing or bending a valve etc. I need to do a compression check. The car seems to be running ok though for now.

[reeves]

Originally Posted by Pepper86

It is a mechanical issue. There are no electronics that can save you from a mechanical over rev. The wheel speed will force the motor to exceed any limiter/limits. I.e. 2nd gear at ~70(mph) is roughly ~9k(rpm). Think about it like jumping out of a moving vehicle. If you jump out of a moving vehicle at 15mph you are either going to instantly run 15mph or eat it. The same with the motor. It is either going to rev to the rpm due to wheel speed or something is going to let go/give. Everything seems to be held together still, however I am worried of any scaring to a bearing or bending a valve etc. I need to do a compression check. The car seems to be running ok though for now.

If it's running ok, just keep monitoring the AFR, engine oil temp, and other vitals with an OBD2 Scanner & the Torque app while you're driving just to be sure.
Looks like you dodged a bullet there.

[Detroiter]

Originally Posted by Pepper86

It is a mechanical issue. There are no electronics that can save you from a mechanical over rev. The wheel speed will force the motor to exceed any limiter/limits. I.e. 2nd gear at ~70(mph) is roughly ~9k(rpm). Think about it like jumping out of a moving vehicle. If you jump out of a moving vehicle at 15mph you are either going to instantly run 15mph or eat it. The same with the motor. It is either going to rev to the rpm due to wheel speed or something is going to let go/give. Everything seems to be held together still, however I am worried of any scaring to a bearing or bending a valve etc. I need to do a compression check. The car seems to be running ok though for now.

I think you guys are misinterpreting what I'm saying. Because you are saying the same thing I am. It is mechanical and the electronics trying to deal with it is what CAN (not every time) cause the tires to give instead of the engine. The electronics could never "magically" stop the laws of physics. What I am saying is the ECU says "hey the engine is past 7600rpm that's not right" so it cuts fuel harshly resulting in a abrupt engine braking throwing a lot of resistance to the drivetrain. This has the potential to disrupt the rear tires enough to lock them up and drag the across the ground (similar to pulling the hand brake). To be fair it isn't actually locking them up but forcing them to spin at a slower rate than you are moving resulting in the loss of traction. If the harsh fuel cut engine braking is not a strong enough of a force to cause the tires to break traction then it will result in the engine over revving to like you said ~9k RPMS.

In your case with going from 6th to 2nd at 70 I'm sure the fuel cut was not enough to save the engine from over revving. If it was you would have heard a loud screech from the tires locking and the tail would have gotten lose and moved around a bit.

[humfrz]

Originally Posted by Pepper86

After getting in the car this morning on my way to work I was practicing going from 6th to 4th and I for sure went to second gear last night. So I probably "zinged" the motor from anywhere around 8.5k-9k(rpm )
No warning lights atm thank God.

Well, I figure ....... if your car is still running ....... it will be OK.

Not to be telling you how to downshift, but I've found that downshifting to the next lower gear ...... causes less shock to engine and drivetrain ......


humfrz