When it has to do with measuring the torque, there are three unique variables within the combustion engine that you must know:
The force produced at a specific RPM: This is the max horsepower of the engine generated at a desired RPM. When an engine accelerates, there is an RPM or horsepower curve. As the engine RPM increases, the horsepower goes up as well, until it approaches a maximum level.
The distance: This is the length of the connecting rod stroke: the longer the stroke, the more torque is produced as we previously explained.
The constant of the torque: This is a mathematical number that is given to all engines, 5252 or the constant RPM where the horsepower and torque are balanced. The number 5252 was gotten from the observation that one horsepower was equivalent to 150 pounds that covered 220 feet in one minute. To express this in foot pounds of torque, a mathematical formula was brought about by James Watt, who invented the first steam engine.
The formula is as follows:
Assume that the force of 150 pounds is applied to one foot of a radius (or circle that’s available inside a combustion engine’s cylinder, for example) you’d have to convert this to foot pounds of torque.
220 feet in one minute has to be extrapolated into revolutions per minute. To perform this, you’d take two times Pi (or 2.141592) which equals 6.282186 feet. Take 220 feet and divide by 6.28 and we get an RPM of 25.014 for each revolution.
Take the 150 feet and multiply times 25.014 and you get 5252.1 – which is our constant that is factored into measuring foot pounds of torque.
How to calculate the torque of a vehicle
The formula for figuring out a torque is torque = horsepower of the engine x 5252, which is then divided by the RPMs.
The issue with torque, however, is that it is measured in two different places: directly from the engine and to the drive wheels. Other mechanical parts then can increase or decrease torque ratings to the wheels include: flywheel size, transmission gear ratios, drive axle gear ratios, and tire/wheel circumference.
In order to figure out the torque to the wheel, all of these items has to be factored into the equation, that is best left to a computerized program included in a performance dyno. On this type of equipment, the vehicle is placed on a rack and the drive tires are placed next to a series of rollers. The engine is plugged into a computer read out that monitors engine RPM, fuel curve, and gear ratios. These numbers are factored with wheel speed, acceleration and shift RPM’s as the car is driven on the dyno for a required length of time.
The calculation of torque of the engine is a lot easier to know. Following the formula above, it’s clear to see how the torque of the engine is proportional to the horsepower and the engines’ RPM as stated in the first article. By using this formula, you can figure out the torque and horsepower ratings at each point of the RPM curve. You must have the engine’s horsepower figures which are generated by the engine manufacturer in order to calculate the torque.