Consanguinity between Torque and Power

Consanguinity between Torque and Power

When people think about automotives the first thing that comes to mind is – all the figures and stats of a vehicle. Out of all, maximum eyes search for the numbers of BHP and torque. Most of us know what BHP and Torque are, but what do they exactly do? Let us take a peek inside.

First of all, let’s shed some light on BHP. Brake-horsepower is a unit of power for measuring the rate at which device can perform a mechanical work. Its abbreviation is HP or BHP. One horsepower is defined as the amount of power needed to lift 550 pound-feet per minute. Horsepower is a measurement developed by James Watt, the inventor of the steam engine, using complex mathematical equations showed that a horse is typically capable of a power rate of 32,572 foot-pounds per minute. Whereas, today the SI unit of power is named after Watt, and One Horsepower is equal to approximately 745.6999 watts.

Horsepower is an indication of how fast a car can ultimately accelerate and thus it is a basic mentality that more power leads to more speed and yes, in a perfect world it can be true. There are various units of power, like Horsepower, Brake-horsepower, kW, Cheval-vapeur, Pferdestärke (PS) etcetera and from all these options car-manufacturers can’t agree to one universal unit of measurement.

Moving further, Torque is a twisting or turning force, it is the tendency of a force to rotate an object about its axis. In automobile engines it is a unit of measurement of rotational effort applied on the crankshaft by the piston. The unit of the Torque in SI is Newton-Meter (Nm), whereas the other units to measure torque are Kilogram-meter (Kg-m) and Feet-pound-force (ft-lb) in imperial / British units.

Different engines are built for different and unique purposes, so the torque produced by engines varies upon its applications. Here are some terms, on which the engine torque depends – Compression ratio, Combustion Pressure, RPM and Stroke-Bore ratio. The amount of torque changes according to how much we rev the engine. For example, let us assume a random car which peaks at 4500 RPM, so the maximum torque for this engine is mentioned @4500 RPM. But running the engine at higher RPM does not result in any more torque; as the torque flattens or decreases.

Torque and Horsepower are unquestionably important measurements for any engine and they are also relative to one another. The Torque Band or Torque Curve stands for the pulling capability of the engine, which also determines engine’s drivability and initial push. Torque is a must to rapidly move the vehicle or operate with ease on slopes; while the horsepower dictates the vehicle’s acceleration. So having a good Power-Torque ratio makes a superb fuel consuming machine.

Making an engine with enough torque and horsepower is not the end of the story, it is also important to have an appropriate balance between them. Every designer has to focus on the balance between power and torque. One has to design in a way that the buyer can understand the importance of both, also one has to keep in mind the crucial factor of power versus aerodynamic drag and torque versus weight. The balance between torque and power determines the vehicle’s purpose in the market.

Here are the formulae to calculate the power and torque:
For Horsepower, hp = (torque x RPM) / 5252
For Torque, Torque = (5252 x hp) / RPM


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