Yeah, Gm installed this feature, I am suprised more guys don't know about it. Its called the "OH **** SENSOR". When you mash the throttle all the way , it gives you that split second to say "Oh ****, I am about to launch like a ****"! Once you adapt to your car, GM will take this sensor out free of charge. Good luck!!

 

Ranger and I have noticed that the limiter in the C6Z can be slow to respond depending on the situation. If the car is in gear and you simply run into the Rev-limit, the RPM rise is slow enough that the PCM respond fast enough and it will invoke one or more of the 3 methods used to stop the RPM's from rising. However, if you run it up to 7000 RPM, then push the clutch in, the rate of RPM rise from 7000 to the RPM-limit will be much faster since there is no load on the engine. In this case, it will blow past the 7100 rev limit, and 7400-7500 will be seen in the data logs.

The 3 methods available to the PCM for RPM limiting are:

1. Fuel Cut - Cutting the signal to the fuel injectors. No signal = no injector pulse. No Pulse = no fuel.
2. Throttle - Closing the Throttle to restrict air.
3. Spark.

The default setting from the factory is #1, Fuel Cut only. However, a tuner can customize the behavior of the RPM limiter to for example have the Throttle close first, then 200 RPM's later, do Fuel Cut.

Regardless of what methods are used, it is important to note that with the current PCM GM is using, RPM limits can and will be exceeded in the condition described above.

 

I knew I wasn't going crazy. My problem is now how do you know exactly what rpm you actually shifted at and where is the limiter, so one can shift just before it.??

 

Hi robz.

To determine the setting of the rev-limiter, you can set up your data logger and go to a safe spot. Then accelerate in first or second until you hit the limiter. The logger will capture the event so long as you're at clutch-out when it occurs.

You can do the same thing using a calibrated GTech-Pro RR. Run a gear clutch-out until hitting the limiter; download the file. The rpm-v-Gforce curve will change abruptly at the limiter rpm.

At the drag strip both HPTuner onboard logging and GTech Pro RR will give you your actual shift points.

Finally, you can calculate the optimal shift points for your modded motor, using your current dyno output in msExcel format. If you have that or can get it from Cartek, let me know; I can talk you through the process.

Ranger

 

Many thanks to Ranger and everyone else for the replies. This thread is very helpful technically.

 

I use HPTUNERS to log the RPM and have figured out how to also log the clutch pedal. So, you can see the exact RPM that the clutch pedal went in, (and in my case, also see the throttle being lifted). However, as noted above, the RPM's will continue to rise once the clutch pedal goes in, and will do so at an increased rate than while in gear. The PCM is slow to respond in this situation and you will definitely see RPM's above the rev-limit. This conclusion can be verified by looking at injector cycle time and seeing that the RPM limiting provisions are not yet invoked.

Data logging is the best way to determine if you're bumping into the limiter.

To determine where your RPM limiter is set and what methods of RPM limiting are being invoked, you can display these parameters with HPTuners or LSxEdit.

Again, if you slam into the Rev-limiter while in gear, it will work as advertised. But my experience shows that putting the clutch in just before the limit will allow the RPM's to quickly rise above the limit - as there is period of time required to lift the throttle.

Rob - Are you power-shifting?