Cylinder Pressure Calculation

[blackbolt22]

Does anyone know how Cylinder Pressure is calculated?

The cookbook suggests using the Cylinder Pressure Limit as a way to put a global limiter on spark so I made mine 16 & then 18 degrees for higher loads but in a WOT pull, sometimes I'm hitting a Cylinder Pressure Limit spark source.

I have the tune only using as much as 14 degrees spark timing however when cylinder pressure limit is triggered the spark is ramped down gradually to 1 degree!

For now I'll put it back to the stock roush settings but I do want a global limiter for spark. I guess I could use preignition limit table instead?

[murfie]

Cylinder pressure is not calculated by the ECU. They would have to model it like they do torque, they are proportional, until a point, so it could be estimated from torque, but the inherent inaccuracy wouldn't make it useful.

The cylinder pressure limit table works by the limit table value triggering a timer. Based on pedal position/ throttle, engine load, and/or RPM a timer and a max retard value is determined. The spark will decrease until the max retard or the time limit is meet. It can be reset is the pedal/ throttle, load, or RPM conditions are no longer meet. There is probably a max retard table thats not defined, mislabeled, or shared with another label like one under the transient section.

I think the preignition table is more commonly used for your purpose.