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A parameter necessary to perform the bench test is the calculation of A parameter necessary to perform the bench test is the calculation of the ratio between the number of engine revolutions and the speed of the car. The ratio is useful for accurately establishing the distribution of torque and power over the operating range of the engine expressed in RPM.For vehicles equipped with C-CAN communication it is possible to perform the calculation automatically by taking data from EOBD. For vehicles not equipped with this communication system, it is possible to carry out the calculation in a few seconds, establishing, before setting, the RPM set used for the selected gear.Once the value is obtained, the power test can be carried out immediately.
A wrong calculation of the ratio leads to a wrong evaluation of the torque value as it is strictly related to the power through the number of RPM:
P = C*ω
With ω which expresses the number of rotations per minute of the engine.
This can lead to serious errors of evaluation that may or may not be desired. By overly changing the ratio between the number of revolutions and speed, very different values are obtained, as shown in the following picture:
Changing the Ratio from the initial value of 47.06 to 27.06, with the same gear, we obtain a different development of the graph (1500-3500 RPM against the real 1500-6000 RPM), and a different value of torque! (48.8 kgm against real 28.1Kgm !!).
So we must always pay attention to any changes to this fundamental parameter that would lead to serious errors in the evaluation of the torque.