You may be familiar with power (usually called horsepower), but you may not know what that other rating means – the torque. Power is simple – the more you have of it, the faster you’ll go. But that only tells you one side of the story. Torque is a better indicator of how an engine will feel in use.
What is Horsepower
When the fuel mixture inside an engine explodes, it generates enormous amounts of pressure. This pushes the piston downward and the power by which is getting pushed downward is known as Indicated Horse Power. This is the maximum power which you can get practically. But the engine is never friction-free. When it moves, the pistons rubs against the cylinder wall, the connecting rod and the piston pin create friction and there are various other parts which generate friction force on movement. When you add all of these(frictional horse power) and subtract it from the indicative horse power, you are left with brake horse power; the power which is available at the end of the crankshaft.
Power is how rapidly work is accomplished. Eighteenth-century Scottish inventor James Watt gave us this handy equivalency: one horsepower is the power required to lift 33,000 pounds exactly one foot in one minute. Honoring that contribution, the SI measurement unit for power is the kilowatt.
What is Torque
The easiest way to think about it is – if horsepower tells you how fast the car can ultimately go, then torque tells you how hard it can push you there. Torque matters as much, if not more so, than horsepower because it’s the force you feel when you accelerate. If you regularly tow a trailer or tourer, or frequently carry a fully-loaded car, then having plenty of torque is important because it helps you pull your load onwards.
The best analogy to describe torque is to compare it to turning a nut with a spanner. Say your spanner is a meter long and you apply one newton of force to the end of it – you’re turning the nut with one newton-meter of force. Double the length of the wrench or the weight applied to its end and you double the torque being applied to the nut. In the UK, torque is typically measured in imperial foot-pounds rather than metric standard newton-meters – one Nm is equivalent to 0.738lb ft.
Torque is a rotating force produced by an engine’s crankshaft. The more torque an engine produces, the greater its ability to perform work. The measurement is the same as work, but slightly different. Since torque is a vector (acting in a certain direction), it’s quantified by the units pound-feet and newton-meters.
How it Works
Back to Berra’s theorem, torque is the capacity to do work, while power is how quickly some strenuous task can be accomplished. In other words, power is the rate of completing work (or applying torque) in a given amount of time. Mathematically, horsepower equals torque multiplied by rpm. H = T x rpm/5252, where H is horsepower, T is pound-feet, rpm is how fast the engine is spinning, and 5252 is a constant that makes the units jibe. So, to make more power an engine needs to generate more torque, operate at higher rpm, or both.
Another issue is accurately quantifying the power and torque from a spinning crankshaft. The tool for this task is an engine dynamometer. While that word means “power measurement device,” in practice the engine’s torque and rpm are measured and its power is calculated using the formula cited above.
The perfect engine produces ample torque at low rpm and sustains that output to the redline. The amount of torque produced is directly proportional to the air flowing through the engine. Large engines pump more air and, therefore, produce more torque. Boosters—superchargers, turbochargers—deliver additional air to help small engines act large. Of course, appropriate amounts of fuel must be supplied to the combustion chambers, but that’s the easy part, especially with electronically controlled injection.
Making up for the ease of injecting the right amount of fuel, engine designers face several difficult tasks. One is making all the components tough enough to handle the loads they’re subjected to by combustion pressure and, in the case of moving parts, their own inertia. Cooling and lubrication needs are roughly proportional to the power produced. And pumping air into, through, and out of any engine at ultra-high rpm is where engineering becomes an art form. Factor fuel efficiency and exhaust cleanliness into the development equation and it’s clear why engine wizards rarely hang out at the water cooler.
At this point of the discussion, it should be clear that torque and horsepower are like estranged siblings; they’re closely related but don’t have much in common.
Well, in short; in a baseball game, if torque is analogous to the catcher, then horsepower is the pitcher. Both are necessary to play ball, but the pitcher’s responsibilities—determining the speed and path of every ball thrown—rule the game. Torque is vital to every engine’s operation, but horsepower is what distinguishes a great engine from a good one.