C6Z06 Rev Limiter Operation

[dgdoc]

Hello:

I have been data logging a 2006 Z06 using HP Tuners and noticed that on shifts, the rev-limiter of 7100 is often exceeded. I've seen RPM readings as high as 7500 RPM. I have been under the impression that the rev limiter was a hard stop and that RPM's could not rise above this - but now I am questioning this.

Would appreciate if someone provide an explanation on exactly how the rev limiter was designed to operate on the C6Z06.

Thanks

[Bill@HPTuners]

mind posting the hpt & hpl files please. And most rev limiters arent a hard stop...you can see a flash of 1000 rpms or more if you miss a shift or something while powershifting(don't ask how I know) lol sometimes the computer just can't react quick enough...although an etc limiter should work better then a spark or fuel limiter because it could literally close the door

[dgdoc]

mind posting the hpt & hpl files please. And most rev limiters arent a hard stop...you can see a flash of 1000 rpms or more if you miss a shift or something while powershifting(don't ask how I know) lol sometimes the computer just can't react quick enough...although an etc limiter should work better then a spark or fuel limiter because it could literally close the door

Well, if it is only ETC based, the RPM's could still rise quite a bit above the limit.

I've attached an .hpl file that illustrates this. Take a look at frames 2578 and 2748.

[Bill@HPTuners]

looking at fram 2746 where it first goes over your rev limiter it takes .05 of a second before it pretty much cuts fuel...mind you theres still some tps action meaning the throttle is going to stay open more then likely making it rev quicker then no tps...im sure the computer needs some time to not only react but every other piece of equipement takes a little time to do its thing.

Also on LS2/LS7 motors use ETC position rather then TPS SAE if possible.

Commanded afr is another good thing to log.

lata
Bill

[dgdoc]

looking at fram 2746 where it first goes over your rev limiter it takes .05 of a second before it pretty much cuts fuel...mind you theres still some tps action meaning the throttle is going to stay open more then likely making it rev quicker then no tps...im sure the computer needs some time to not only react but every other piece of equipement takes a little time to do its thing.

Also on LS2/LS7 motors use ETC position rather then TPS SAE if possible.

Commanded afr is another good thing to log.

lata
Bill

I have uploaded the stock tune file for a 2006 Z06. In this file, it shows the RPM limit by gear set to 7100 RPM. The Extreme Cut-off is set to 7200. It also shows that the method of controlling RPM is to use "Fuel-cut" and the ETC and Spark check-boxes are not selected.

Looking at the data logged, there is no sign that the fuel was cut to the injectors when the RPM's exceeded either 7100 or the "Extreme Cut-off" at 7200 RPM. However, you can see the ETC change after some period of latency where the RPM's were allowed to climb to 7500 -- which most people would not consider to be a good thing for the longevity of the engine. Because ETC is not selected as a method of RPM control, I consider this to be associated with Torque Management.

I guess I don't understand exactly how effective GM's current RPM limiter is on a high performance engine like the LS7 - especially when shifts are occuring at 7000 RPM and the clutch goes in. It seems that any latency in controlling the RPM's could allow dangerous RPM levels to be reached.

Maybe the PCM is simply too busy with everything going including processing of the TM algorithm and as a result, it causes delays in processing the rev-limiter function. However, you would think that RPM regulation would be of the highest priority - especially with the (expensive to replace) LS7.

My final question is regarding "fuel-cut". By "fuel-cut" I assume this to mean that the fuel-injectors are immediately shut off -- and there is no more fuel delivered to the cylinder so the RPM's can not rise. Is this correct?

Thanks again.

[dgdoc]

Anyone want to weigh in on this?

[Chris@HPTuners]

the new ECM's have Spark, ETC and Fuel methods to control RPM, they also have an acceleration based limiting feature that brings the limiter in early to prevent overshoot (if its calibrated). Generally, it's not calibrated though.

a free revving engine will have quite a lot of intertia that simply cutting the fuel will not immediately stop, hence the acceleration based stuff.

Chris...

[dgdoc]

Chris:

Could you provide some additional information or insight on how the acceleration based tables and parameters work?
- Filter Coefficient
- Accel Threshold
- Accel Max

Thanks in advance.

[andrew barrale]

subscribing

[dgdoc]

Chris - Can you provide any info on this?

Thanks.

[EC_Tune]

Just a question:
Since a stock 2006 Z06 makes max power at ~6400 RPM, why are you revving to 7000+ in the first place? That's harder than hell on those stock beehive single wire springs. Break one of those and it's instant dropped valve and the motor's history.

[redhardsupra]

blue is powerband, pink is what power you'd actually use with normal shiftpoints.
this is an example for a stock LS1 with A4 gears, but the idea is the same. it's not about how much you won't gain up top, but about how much you wont lose on the bottom. look what kind of power you shift to if you shift early

[EC_Tune]

I still wouldn't trust those beehives at +7000+ RPM...

Yes I know you have to over rev for the crappy 1-2 shift on a 4L60E/700-R4/whatever they are calling the POS these days. And the Z06 has a much different gear ratio package in the six speed than the crappy 700-R4/4L60E series that hasn't *significantly* changed mechanically since 1982.

Gear ratios: M12
First: 2.97 Second: 2.07 Third: 1.43 Fourth: 1 Fifth: 0.84 Sixth: 0.57 Reverse:2.9


Gear ratios: 700-R4/4L60E/4L65E/4L70E
First: 3.06 Second: 1.63 Third: 1 Fourth: 0.7 Reverse: 2.29
BTW: The much vaunted dry sump on the LS7 isn't so great either from my sources in the dry sump world. They basically stop being a "dry sump" at about 4500 RPM as the pump can't keep up with evacuation demands.

[dgdoc]

The answer is that the HP at 7000 is still higher than it is when it enters the next gear at around 5000. So, the "area under the HP curve" is maximized in this way. Folks like Ranger on CorvetteForum have run 10.85 with a stock C6Z06 by understanding this principle.

You are correct that there seems to be an issue with the quality of the valve springs on the C6Z06 that is starting to show up -- with catastrophic results when it fails.

http://forums.corvetteforum.com/show....php?t=1574667

So, getting back to the subject at hand -Can anyone explain the parameters associated with the rev-limiter posted in the question above?

[Joe_G]

Chris:

Could you provide some additional information or insight on how the acceleration based tables and parameters work?
- Filter Coefficient
- Accel Threshold
- Accel Max

Thanks in advance.

I can tell you this - I put a set of 390 gears in my basically stock LS2 (vararam, ported intake and headers) and the Accel Threshold limiter was kicking in at 5800 in 2nd gear only. It felt just like the rev limiter on a LS1 - a harsh spark cut. The normal rev limiter in the LS2 is a lot softer. I set all the values in the table to 0 and no problem anymore. So it does work under certain circumstances for sure.

Sorry I can't explain it any better - I bought Tuners just to fix this problem, so I'm still learning.

More details linked here:
http://www.hptuners.com/forum/showthread.php?t=8611

[EC_Tune]

There is an 07 Solstice and an 07 Vette in the Tune Repository. Do a compare and it may give you more insight into how the acceleration based RPM limiting is utilized as the RPM Limits are very close. The Vette seems to be more active in lower gears than the Solstice on the accel based limiting and actually has some values in the Accel Thresh table.