Torque is leverage, measured in Newton-metre, pound-foot etc. For example, when you tighten the
bolt using spanner, torque that you applied is your applied force x the spanner length. It is independent of speed.
Horsepower is another name for power which is energy expenditure per unit time. measured in
joules per sec i.e. Watts
The above 2 concepts are related.
Torque x rotational speed = power (kW) or horsepower (hp)
(one horsepower = 0.746 kW)
So in the spanner example above, power depends on how fast you turn the spanner, even if the torque remains the same.
Yes torque determines how much you can accelerate the car, and so is horsepower which not only
accelerates but at what speed at that time. They are not really independent stuff, just what
kind of measurements are involved. Horsepower depends on torque AND speed at any one time.
TECHNICAL STUFF:
Torque of 4G13 engine is 109 Nm @ 4000 rpm (measured at crankshaft).
1st gear ratio = 3.363, final drive gear ratio = 4.322
The gearbox thus reduces the 4000 rpm to 275 rpm while increasing torque to 1584 Nm.
Radius of tire 175/70R13 = 0.288m,
Since torque = force x radius arm, you can calculate the pushing force to be
1584 / 0.288 = 5509 N which is equivalent to 561 kg force.
This means a force equivalent to 561 kg is pushing your car forward in gear 1 at 4000 rpm.
The power that generated at the engine = Torque x rotational speed
= 109 x 4000 x 2 x 3.142 /60 W = 45,664W = 45.664 kW = 61 hp approx.
This is the amount of energy extracted from burning petrol per sec and translated to engine
shaft output.
The power mentioned here is the same thing as in your household appliance like 2000W kettle,
50W lamp etc.
Torque can be increased or decreased by way of the gearbox. Power remains nearly same, i.e.
reduced slightly by frictional losses passing throught the drive chain.
At gear 1 & 4000 rpm, the speed is 30 km/h. The road friction & wind resistance is about
17.8kg, so the balance from the 561-17.8 = 543.2 kilos of force suppled at the wheel is to
accelerate the car.