It is very easy to calculate dRPM / dt, which is proportionate to torque. However, when doing tuning runs, you want to be able to compare the result after changes (like changes in ignadv).
Analyzing the logged runs, in RPM-bins, in a similar way as lambda, VE and ignadvn is tuned is very helpful. Something like this (except for real data, and colored nicely):
| RPM | 3000 | 3500 | 4000 |
| MAP | 110 | 140 | 170 |
| ignadv | 24 | 25 | 27 |
| EGT(C) | 552 | 603 | 612 |
| lambda | 0.82 | 0.81 | 0.8 |
| torque dRPM/dt | 1600 | 3100 | 3900 |
RPM => power calculation is very simple
Some of the input parameters are often estimated though (a well known such parameter: m=mass, you can measure that too, of course)
- P=F*v
- F=m* (dv/dt + anull) + Fnull
- where anull = g*slopepercent (like g*0.04 for a 4% slope to keep the car climbing without deceleration)
- Fnull = some force to keep the car running without decel even on a 0 slope. Fnull=500N means that 500N * 20m/s = 10kW sounds reasonable below 100km/h (at high speed this climbs as v**2, due to air drag)
- so P=v* (m* (dv/dt+anull) + Fnull)
- v = RPM * const
- where, with audi in gear2: const = 1/2.13/4.11 * wheel_circumference
- wheel_circumference=1.87m (if you measure diameter and calculate 0.6m * pi, you get 1.885m, but remember the tyre is somewhat pressed in)
- so the audi wheelspeed at 7000 RPM and gear2: 7000 / 60 /2.13/4.11 * 1.87 = 24.9 m/s = 89.7 km/h
dRPM/dt => Nm (torque) calculation
So (with the 1600kg audi in gear2) what is the const in the torque=const * dRPM/dt to get the result in Nm ?
- dRPM / dt is given
- as in the upper formula, force on the wheels: F=m* (dv/dt + anull) + Fnull
- wheel torque Mwheel = F / wheelradius
- motor torque Mengine = Mwheel / drivetrain = Mwheel / 2.13/4.11
- v (in m/s) = RPM/60 / 2.13/4.11 * wheel_circumference
- m=1600kg (1400kg + spare tyre + fuel + 2 persons)
- wheelradius = 0.3m
- Fnull = 500N
- anull = 0.03 * 9.81 m/ss