Figure shows the power and torque characteristic of a reciprocating internal combustion engine.
Apart from the characteristic, the fuel consumption map (next slide) is an important basis for matching the combustion engine, converter characteristic and motor vehicle. In this case the mean effective pressure pme is plotted as a function of the engine speed nMot.
Considering the torque over speed: 
The minimum speed nmin is required. In the context of the characteristic curve:
The induced mean pressure pmi (and hence the power) in case of the Otto engine depend on the cylinder's degree of filling.
An increased vacuum in the intake manifold improves with speed.
Heat losses (e.g. on the cylinder wall, ...), leakage losses (e.g. piston rings, ...) become smaller.
With higher speeds the degree of filling decreases as a result of rising flow losses in the inlet and outlet ports (throttle losses), apart from mechanical losses which also increase.
The mean effective pressure pme reaches its peak value at the medium speed range and thus a maximum for the engine moment. The product of M with n results in the characteristic of P over n.