What is meant by torque of an engine?

Question

For torque we need to specify the radius.So what is the radius parameter in an engine?How is this torque calculated?

Answer 1

The torque of an engine is the "rotational force" that the pistons transmit to the crankshaft. It is what the engine is designed to produce. Powerful engines produce high torque. The product of the torque T and angular speed w gives you the power P of the engine:

                                    P= wT

When the torque is reduced by the gearbox the speed is increased thereby keeping power constant.

Answer 2

Torque is the measurement of rotational energy the engine supplies. Since this energy is transferred from the engine to the transmission, it makes sense to use the radius of the flywheel in calculations.

Answer 3

Torque is a measure of power output per unit speed.

Using Imperial units:

Torque (lb.ft) = (Shaft HP) / (Shaft RPM) * 5252

Using metric units:

Torque (N.m) = (Shaft kW) / (Shaft RPM) * 5195

No radius required.

Answer 4

Force applied over a radius produces torque.  In an internal combustion engine the force is generated from the expanding products of combustion applied over the surface area of the piston.  This load is transmitted down the connecting rod and into the crankshaft.  The radius that the force is applied is the length of the throw of the crankshaft (the distance from the crankshaft main journal centerline to the centerline of the crank's rod journal).