BMW M5 Forum and M6 Forums banner

1 - 6 of 6 Posts

·
Registered
Joined
·
353 Posts
Discussion Starter #1
First off, if the answer is simply "that's how it works", I'm pretty ok with that.

I don't know how to articulate it very well but comparing to other vehicles, the S85 rev limiter is managed a little differently. I say that because there's no "ting ting ting ting ting" when you hit the limiter, but instead a whole engine retardation. What's this called in comparison to other types of rev limiting where just the spark is skipped?

The perfect storm of "oh no wtf was that" is when you've pinged the redline and you shift a little too late, so the shift is made during this rev limiter sequence. The process takes a little longer to find the next gear, presumably because the transmission can't match revs with what should-be, but which is now rev limited, during this short window. The result is incredible acceleration, then feeling like you're stuck in tar, and then pulling in to a higher gear at lower RPM - and the following sensation is a gentle reminder of how Grandma would be driving.

"Don't abuse the redline on a tired overly-excited motor" anecdotes aside, is this engine management working as designed, or is what I describe a sign of greater trouble? No codes, recovering in a lower gear brings everything back the way I want it, but it's that slight moment of panic that I'm pretty sure is just me overthinking things.
 

·
Moderator
Joined
·
2,504 Posts
Soft limiter - hate it. One of my questions to Jim was whether he could change this to a hard limiter (ie fuel cutoff). Don't recall getting an answer...
 

·
Registered
2009 BMW E63 M6, Sapphire Black
Joined
·
459 Posts
hmmmm, not sure if I have experienced that. I just get my head slammed back as I shift gears. maybe not hitting the limiter ???? seems like I read somewhere that torque curve drops before hitting red line anyway, something along that line.
 

·
Registered
Joined
·
353 Posts
Discussion Starter #4
Yeah! That's the sensation I enjoy when the gears hit just right hah!

Also, it's a lot more pleasant these days with new diff, motor, and transmission bushings!
 

·
Registered
Joined
·
285 Posts
Yeah it’s a soft limiter which I believe is actually a fuel cut type limiter. The ignition cut style rev limiters give that sharp sound (and often flames). In fact for flat shifting (ie clutchless upshifts) you use a short ignition cut which unloads the drivetrain allowing a rapid gear change without using the clutch.

It makes me wonder if the m5 uses the clutch for full throttle high rpm upshifts (especially in s5 or s6). It feels to me like a clutches shift using a brief ignition cut, given how fast and hard the shifts are it seems unlikely it’s using the clutch. Does anyone know?
 

·
Registered
Joined
·
1,217 Posts
Yeah it’s a soft limiter which I believe is actually a fuel cut type limiter. The ignition cut style rev limiters give that sharp sound (and often flames). In fact for flat shifting (ie clutchless upshifts) you use a short ignition cut which unloads the drivetrain allowing a rapid gear change without using the clutch.

It makes me wonder if the m5 uses the clutch for full throttle high rpm upshifts (especially in s5 or s6). It feels to me like a clutches shift using a brief ignition cut, given how fast and hard the shifts are it seems unlikely it’s using the clutch. Does anyone know?
you can log the clutch opening in testo and find out, I'd assume it is using the clutch but opens it only as much as it's needed to keep the lag as short as possible.
 
1 - 6 of 6 Posts
Top