E38 (2007 Z06) rev limit overshoot

I have a very light (17 lb) Tilton clutch and flytwheel setup in my C6, and noticed the rev limiter did a very poor job at limiting revs during first gear wheelspin or revving in neutral. I've logged RPM as high as 7600 with extreme cutoff set to 6600.

So I set the extreme cutoff to 4000 and tried a few different things to see if I could get the limiter to kick in instantly (my latest tune is attached). Unfortunately nothing worked. I then logged a few things to try and figure out what was going on. I exported this log without interpolation (though I did manually interpolate rpm) so I could try and figure out the timing of events: https://docs.google.com/spreadsheets...mWtSQwy_TU1DYk

Part of the problem seems to be that fuel cut is not activated until the motor is past the rev limiter, sometimes hundreds of RPM past. The other problem is the engine continues to accelerate even after the rev limiter is activated, even though spark and fuel cutoff were enabled. Injector pulse width does not simply drop to zero as expected, but tapers off. I'm not sure when or if spark gets cut, as I'm not sure how to log that. The limiter finally starts to work around the time throttle position drops (on it's own, even though the ETC limiter is disabled). I'm not sure if this is coincidence, or it's the throttle closing which actually limits the motor. The dropping injector pulse width could just be a result of the throttle closing and dropping MAP.

The result is I rev as high as 5268 with a 4000 RPM extreme cutoff.

Is the only solution to this a very heavy clutch and flywheel setup? I suspect a stock pressure plate with a light flywheel would still significantly over-shoot. I'd love to be able to enable flat shifting via the park / neutral settings. The delay in starting fuel cut would even be acceptable if it just cut fuel and/or spark instantly, but it clearly does not. Maybe the solution is just an aftermarket rev limiter and two step box.

Thanks for any help.

the limiter settings are not right, use spark and ETC and disable fuel cut, then put the switch over delay to 1 sec, with the commanded torque which is -8192 make that all 400, the extreme cut make that 300 above the "in gear" and make the cold engine same as the in gear limit, the commanded torque delta table make the positive side all 300 leave zero column as zero, see how those go u may have to adjust it a little, also if u have stock file try those settings and adjust from there

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Originally Posted by 07GTS

the limiter settings are not right, use spark and ETC and disable fuel cut, then put the switch over delay to 1 sec, with the commanded torque which is -8192 make that all 400, the extreme cut make that 300 above the "in gear" and make the cold engine same as the in gear limit, the commanded torque delta table make the positive side all 300 leave zero column as zero, see how those go u may have to adjust it a little, also if u have stock file try those settings and adjust from there

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Thanks, I'll try those settings and report back.

I did start with stock settings; that's how I saw 7600 RPM. The above settings are just where I ended up after a lot of fiddling (none of which did any good).

also go into the operating system tab and enable the TCS patch and do write entire as u will need that once SD, and raise up the dynamic airflow high/low above 8000rpm if not using maf, and the maf fail high set to 2 and low to 1, also high and low counts to 0 will help it fail faster

Since your in there messing with rev limit, how does a soft non-jerky, non-overreving smooth limit sound?

you can play with table 12070 - Cmd Torque Delta - Increasing the values starting at 0rpm and higher, say -100 at 0rpm, -200 at 100rpm, -400 at 200rpm, -550 at 300rpm, and so on will cause it to pull so much timing or Throttle if you have DBW that it will act as a soft rev limiter. Keep your RPM limit low for now and play with it.

For this to work, I have:
Extreme Cutoff is 6700,
In-Gear cutoff is 6550, If I remember correctly it starts acting at 6550. Extreme Cutoff is still active but I don't get that high with these settings.
Extreme resume at 6620,
Hysteresis 300,
Spark Disabled,
Fuel Cut Enabled,
ETC Enabled.
Switchover Delay is 3sec.


Not sure if the 12073 needs setup for this or not, I have 400 in first gear to 5600rpm, then 300 at 6400rpm, and 25 at 7200rpm
2-6 gears 500rpm to 5600rpm, 460rpm for 6400, andf 25rpm for 7200.

This works great on my 2010 LS3 Camaro Whipple even with all that boost. Not sure how a 2007 will react but it's an E38 so maybe it will work.

Well this was my first attempt at recreating your tune 10_SS. The results were the same as my original ones; 5335 RPM peak on a 4000 RPM extreme cutoff. On the worst over-rev, the rev limit flag in the PCM does not seem to be set until somewhere between 4741 and 4983 RPM.

Are you sure you aren't getting overshoot? What Hz are you logging RPM?

Ok I think I found the problem. I can only get one of the rev limit strategies to work at once. With only spark cut enabled the RPMs are limited to just over the extreme cutoff. If I enable ETC with no delay it goes all the way to 5300+ again. If I switch the delay to 1 second it seems to give the ETC enough time to switch over once the spark cut has done its thing. If I enable fuel cut too nothing changes; injector pulse width stays high while it's bouncing off spark cut.

I tried both fuel and spark cut earlier and it only acted like fuel cut was active. I'm not sure why.

So if you want an extreme rev limit that eliminates overshoot, spark cut works.

the ecm12073 u have zero in the 4000rpm and above, that is what it uses when the limiter is active so if its zero then it wont do anything once active, look at your engine torque pid and use those values to see what torque u need to use to hold the limit at the rpm u want, the ecm12070 just controls the error above and below the limit rpm so if u use enough torque reduction to stop the rpm overshoot and then keep the torque below it smaller so it dosnt reduce and then shoot the revs back over the limit again, so dont have the zero column populated as when its working right u dont want it to be trying to still remove torque think if that table as like an idle error above and below to keep it at zero error

Quote:

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Originally Posted by Grant

Well this was my first attempt at recreating your tune 10_SS. The results were the same as my original ones; 5335 RPM peak on a 4000 RPM extreme cutoff. On the worst over-rev, the rev limit flag in the PCM does not seem to be set until somewhere between 4741 and 4983 RPM.

Are you sure you aren't getting overshoot? What Hz are you logging RPM?

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Sounds like you have it figured out, but HPT logs are 20hz, and here is a 50hz log I used other equipment direct from the crank/cam signals.. (Megasquirt MS3):

That green line is the Throttle blade, not the pedal.

This was cold Goodyear F1 G2 fast and bad wheelspin.

Attachment 96889