How does the Torque Model work in GPRP Pro

One of the key characteristics that sets GPRP Pro apart from other firmware in the GP suite is the use of a Torque Model, which is central to the way many of the control strategies operate.

Using a torque strategy is beneficial because it is relatable to other tuning aspects, such as acceleration. Engine cylinder cut events or ignition timing changes are also relatable to a reduction in torque, so implementing such a model allows multiple methods of controlling torque to be integrated together with predictability.

The torque modelling in our Pro Packages is simplified as much as possible for ease of tuning, and while there are many factors that affect torque in a small way that are not compensated for in the implemented model, this is of no concern for fuel and ignition control and it is well suited for the intended purpose.

As torque is related to airflow, all throttle commanded positions are derived from the Torque Aim system. For example, the Throttle Pedal in most systems sets a Throttle Servo Position Aim, but in GPRP Pro it sets a Torque Aim. This allows the throttle to give a more linear and consistent response. Likewise, in other GP Packages many systems that command a Throttle Aim, such as Anti Lag, now command a Torque Aim.

Torque Generated
The amount of torque the engine produces is closely linear to the mass of air inducted into the engine for each firing. The model is based on Engine Load (mass air per induction) which is calculated in the Engine Efficiency model for fuelling requirements. This is translated to torque using the Torque Ideal Generated scale, a user definable parameter to turn the torque ideal output into an accurate representation of measured engine torque output.

This parameter defines how many milligrams of calculated engine load are required to generate a newton metre (Nm) of torque. As this is all calculated per firing, the value is then multiplied by the number of cylinders to produce the Torque Ideal Generated value. This value includes all torque generated by combustion, not including internal frictional losses and driving of ancillary loads like the alternator, water pump, power steering pump, A/C compressor and transmission oil pump.

Torque Loss via Friction
The Torque Ideal Correction Internal Loss table is provided to correct for the engine’s internal frictional losses and ancillary loads. This table compensates for an average load of most constant ancillaries referenced to Engine Speed and does not compensate for switched loads, such as the A/C compressor. The losses of these larger switched loads, or loads that vary independent of engine speed, are accounted for in the Torque Ideal Correction External Loss calculation. Because additional losses can occur due to high cylinder pressure, piston to bore friction from increased heat, and piston ring friction (particularly in cases where a gas ported piston is used), a Torque Ideal Correction Engine Load table is provided. This table should be calibrated to 0 Nm in overrun and light load conditions – these losses are covered by the Torque Ideal Correction Internal Loss table previously discussed.

Torque Ideal and Timing Gain
The resulting value is Torque Ideal, representing the torque produced based on the air inducted. The final Torque value includes compensations for ignition timing reductions (Torque Reduction) and Fuel and Ignition Cut Estimates.

The torque compensation due to ignition timing reduction is presumed to be linear to simplify the calibration. The Torque Ideal Ignition Timing Gain sets the percent of torque reduction per degree of ignition timing retard.

In a simplified example (excluding internal loss), where the Torque Ideal Ignition Timing Gain value is 1.3%/° :
20° RTD would reduce torque by 26%, so if Torque Ideal was 400 Nm, the Torque would be 296 Nm, 26% less.

The model also presumes optimum Ignition Timing is tuned in the Ignition Timing Main table. If ignition timing is reduced to prevent knock, the calculated torque will be noticeably greater than actual torque. This higher calculated torque during knock is not normally a concern and has minimal impact on the control systems in almost all operating conditions.