[Geighty7]

Just curious- is it true that with modern cars, it’s potentially near impossible to “over rev” on RPM’s unless just sitting on it?

Context- after lots of warming, I punched it in 1st gear and banged limiter a few times before smacking into second. Almost sounds like a sort of anti-lag or drill bit when bouncing. I am not sure if this is good for the car, but don’t think it’s “bad” if not held there for long time periods. I usually shift right before that point, but a handful of times I let it smack rev limiter for about a second before shifting. That’s when I get that noise.

To me, this is different than the limiter bounce when doing a burnout due to actually having traction on the rear wheels.

Anyone smarter than casual self proclaimed car expert me know more about this system and what’s actually happening? Is it fuel cut off, or just modulated by the ECU to prevent engine damage.

I assume the S58 can go above the limiter, especially the manual without torque converter (which I have).

Thanks

[aerobod]

Originally Posted by Geighty7

Just curious- is it true that with modern cars, it’s potentially near impossible to “over rev” on RPM’s unless just sitting on it?

Context- after lots of warming, I punched it in 1st gear and banged limiter a few times before smacking into second. Almost sounds like a sort of anti-lag or drill bit when bouncing. I am not sure if this is good for the car, but don’t think it’s “bad” if not held there for long time periods. I usually shift right before that point, but a handful of times I let it smack rev limiter for about a second before shifting. That’s when I get that noise.

To me, this is different than the limiter bounce when doing a burnout due to actually having traction on the rear wheels.

Anyone smarter than casual self proclaimed car expert me know more about this system and what’s actually happening? Is it fuel cut off, or just modulated by the ECU to prevent engine damage.

I assume the S58 can go above the limiter, especially the manual without torque converter (which I have).

Thanks

Normally there are 4 mitigating strategies as the rev limit is near to prevent over-revving, typically in the order listed to prevent sudden power loss:

- timing retarded
- boost reduced / wastegate opened
- ignition cut
- fuel cut

All will affect the engine noise to some degree. There is no reason the engine should go above the rev limit due to throttle application, if the strategies are applied correctly. Under load there isn’t any problem hitting the rev limiter, but just revving the engine without load up to the limiter can potentially cause issues due to the faster component acceleration and consequent higher loads on components such as the valve train. As many manufacturers do, BMW may put a lower rev limit on the S58 when unloaded, except for brief throttle blips when down-shifting.

[Dave07997S]

You can still do a mechanical over rev. Ie: down shifting into 2nd at 100mph. If you have an auto it's impossible as the auto won't allow it to shift down.

[Slick1984]

Originally Posted by Dave07997S

You can still do a mechanical over rev. Ie: down shifting into 2nd at 100mph. If you have an auto it's impossible as the auto won't allow it to shift down.

Why would you want to do something like that? Seriously …?

[Geighty7]

Originally Posted by aerobod

Normally there are 4 mitigating strategies as the rev limit is near to prevent over-revving, typically in the order listed to prevent sudden power loss:

- timing retarded
- boost reduced / wastegate opened
- ignition cut
- fuel cut

All will affect the engine noise to some degree. There is no reason the engine should go above the rev limit due to throttle application, if the strategies are applied correctly. Under load there isn’t any problem hitting the rev limiter, but just revving the engine without load up to the limiter can potentially cause issues due to the faster component acceleration and consequent higher loads on components such as the valve train. As many manufacturers do, BMW may put a lower rev limit on the S58 when unloaded, except for brief throttle blips when down-shifting.

Super insightful. Was under load during that quick moment. From what I’m understanding on what you wrote, those strategies worked as intended during that case. Thanks for the deep dive, really helpful.

Originally Posted by Dave07997S

You can still do a mechanical over rev. Ie: down shifting into 2nd at 100mph. If you have an auto it's impossible as the auto won't allow it to shift down.

Agreed, ye ole “Money Shift”.
Aka my biggest fear.

[Geighty7]

Originally Posted by Slick1984

Why would you want to do something like that? Seriously …?

I think he was just giving an example of a possible over rev damage situation. Not implying anyone “wants” to do that.

[DSTR]

Originally Posted by Geighty7

I think he was just giving an example of a possible over rev damage situation. Not implying anyone “wants” to do that.

This^^^^^^^^ he was not at all recommending it

[eluded]

The money shift, 3>2.

Originally Posted by Dave07997S

You can still do a mechanical over rev. Ie: down shifting into 2nd at 100mph. If you have an auto it's impossible as the auto won't allow it to shift down.

[robopp]

Yep, attemtping to go from 3>4, but actually going from 3>2. Boom!

[two_three_two]

is it possible for the car to "money shift" with the auto-rev match feature on? I find it hard to believe the car would allow that- but i truly dont know. would the car recognize the error and prevent itself from matching high enough to hurt the engine?

[WhiteRqbbit]

Originally Posted by two_three_two

is it possible for the car to "money shift" with the auto-rev match feature on? I find it hard to believe the car would allow that- but i truly dont know. would the car recognize the error and prevent itself from matching high enough to hurt the engine?

Auto-Rev is not going to assist in anything related to this, engine going to go boom given the situation as mentioned

[xtougher]

Originally Posted by two_three_two

is it possible for the car to "money shift" with the auto-rev match feature on? I find it hard to believe the car would allow that- but i truly dont know. would the car recognize the error and prevent itself from matching high enough to hurt the engine?

This is an interesting question. My first car (2000 Honda Civic) actually sort of "blocked" me from being able to shift into 2nd if I was going too fast. I just sort of thought it was a safeguard to prevent this very thing.

As I put slight pressure to get it into 2nd while slowing down, it would finally allow me to shift into second when I've slowed down enough. Never thought too hard about it or researched it, but this reminded me.

[abrandonment]

I know exactly what you're talking about but I always assumed that was being limited by the speed at which those lower gears were spinning.

[two_three_two]

Originally Posted by WhiteRqbbit

Auto-Rev is not going to assist in anything related to this, engine going to go boom given the situation as mentioned

the question is whether the rev-matching software is smart enough to prevent a mechanical overrev should i still be holding the clutch in but accidentally select 2 vs 4 in the above scenario. i get that if you drop the clutch all bets are off

[robopp]

Originally Posted by two_three_two

the question is whether the rev-matching software is smart enough to prevent a mechanical overrev should i still be holding the clutch in but accidentally select 2 vs 4 in the above scenario. i get that if you drop the clutch all bets are off

The ECU cannot mechanically over-rev without user input. It will rev match to redline, but once you drop the clutch redline will be exceeded.

[RockCrusher]

Originally Posted by abrandonment

I know exactly what you're talking about but I always assumed that was being limited by the speed at which those lower gears were spinning.

That's it. A downshift from 2nd to 1st at high engine speed requires the very best of rev matching as the difference in the speed of the 2nd and 1st gear gears is the most.

If the rev match isn't that good the 1st gear synchro takes time to spin the 1st gear up to speed for engagement to happen. This can feel like there is something prohibiting the shift but there is nothing but inertia at play.

Once I encountered this when I almost shifted from 3rd to 2nd rather than from 3rd to 4th. This in my Boxster. Fortunately I felt the "resistance" when moving the gear lever towards 2nd and realized what I was about to do and pulled the gear lever back in one big hurry. No harm done but my heart was a thumping for a while after...

[two_three_two]

Originally Posted by robopp

The ECU cannot mechanically over-rev without user input. It will rev match to redline, but once you drop the clutch redline will be exceeded.

thanks rob. that makes sense to me. if you're especially worried about money shifting, leaving that feature on seems like a "first line of defense" and should give you a split second to realize you fucked up before you blow up a $30k motor!

[Geighty7]

Originally Posted by RockCrusher

That's it. A downshift from 2nd to 1st at high engine speed requires the very best of rev matching as the difference in the speed of the 2nd and 1st gear gears is the most.

If the rev match isn't that good the 1st gear synchro takes time to spin the 1st gear up to speed for engagement to happen. This can feel like there is something prohibiting the shift but there is nothing but inertia at play.

Once I encountered this when I almost shifted from 3rd to 2nd rather than from 3rd to 4th. This in my Boxster. Fortunately I felt the "resistance" when moving the gear lever towards 2nd and realized what I was about to do and pulled the gear lever back in one big hurry. No harm done but my heart was a thumping for a while after...

I noticed this when attempting a 3 to 2 shift moving at about 65-ish mph into a tight turn on track. Resistance even before the rev match kicked in. I realized then that the car simply was telling me what you explained about the inertia. I could have forced it in and likely rev matched to redline and still wouldn’t have money shifted as 2nd gear on a flat surface tops out at 70-71mph at 7.2k rpm, but I did not push it.

Originally Posted by two_three_two

thanks rob. that makes sense to me. if you're especially worried about money shifting, leaving that feature on seems like a "first line of defense" and should give you a split second to realize you fucked up before you blow up a $30k motor!

I leave it on always, even if people heel toe shame me lol.

[RockCrusher]

Originally Posted by Geighty7

I noticed this when attempting a 3 to 2 shift moving at about 65-ish mph into a tight turn on track. Resistance even before the rev match kicked in. I realized then that the car simply was telling me what you explained about the inertia. I could have forced it in and likely rev matched to redline and still wouldn’t have money shifted as 2nd gear on a flat surface tops out at 70-71mph at 7.2k rpm, but I did not push it.

I leave it on always, even if people heel toe shame me lol.

Forcing the shift even if the shift won't cause an engine over speed condition is to be avoided.

It forces engagement before the involved hardware are spinning at close enough to the same speed for the gear dogs to engage. This causes the teeth of the gear dog to become rounded and this can result in the transmission popping out of gear.

There is increased wear of the shifting fork and even a risk of bending a shifting fork.

[Geighty7]

Originally Posted by RockCrusher

Forcing the shift even if the shift won't cause an engine over speed condition is to be avoided.

It forces engagement before the involved hardware are spinning at close enough to the same speed for the gear dogs to engage. This causes the teeth of the gear dog to become rounded and this can result in the transmission popping out of gear.

There is increased wear of the shifting fork and even a risk of bending a shifting fork.

Thou shall not force shifts. Haha. Thank you for the insight, very valuable for any 6MT who comes across this thread when dealing with downshift questions.

[rk95]

Originally Posted by two_three_two

the question is whether the rev-matching software is smart enough to prevent a mechanical overrev should i still be holding the clutch in but accidentally select 2 vs 4 in the above scenario. i get that if you drop the clutch all bets are off

It will stop you to a point. If you money shift and the RPM’s skyrocket, the computer won’t let the RPM’s go beyond redline with the clutch in. If your foot is still on the clutch, and you hear the roar of the RPM’s skyrocket, if you don’t let the clutch out you will not money shift. Just quickly go back into neutral

[WhiteRqbbit]

The computer cannot overcome the mechanics, regardless of whether there is rev assist. Rev assist is just throttle blipping since it's DBW—unless there is a mechanical lockout, you are going to money shift.