Torque is a rotational force applied to an object or it can be described as the force used to rotate an object around a central axis (usually the central axis of the object itself).
  Some simple examples of applying torque to an object will be the peddling action when riding a bicycle or using a wrench to tighten or loosen a bolt or nut.
  Torque is calculated using force multiplied by distance. Using the bicycle example you will apply a force using your foot and a bigger gear wheel increases the rotational distance where the force is applied thereby increasing the torque. Using the wrench example holding the wrench further up the handle increases the amount of torque you can apply.
  During the four stroke cycle in the power stroke when the explosion occurs it forces the piston down (or across in a boxer engine) and this force through the connection rod rotates the crankshaft. Increase the power of the explosion and the torque will be increased.
  For vehicles this rotating force cannot be used in its raw form, it must be controlled through the transmission to allow the vehicle to idle, reverse and drive using the same rotational action. High end vehicles further control their application of torque which allows certain all wheel drive and torque vectoring systems along with traction control and stability control to send torque to the wheels that need it most instead of always sharing it equally.
  Torque is measured in either Newton metres (N.m) or pound feet (lb-ft). Newton metres is the metric (SI) documentation and pound feet is the English documentation, think of kilometres and miles to measure distance. Their conversions are 1 N.m = 0.737 lb-ft and 1.356 N.m = 1 lb-ft so a vehicle with 400 lb-ft of torque can also be documented as having 543 N.m.
  Some popular examples:
The Cadillac CTS-V with 551 lb-ft or 747 N.m
The Mercedes Benz E63 AMG with 631 N.m or 465 lb-ft
The Bugatti Veyron 16-4 with 922 lb-ft or 1250 N.m.
  With the power and weight principle diesel engines produce more torque than petrol engines of the same size with a higher top dead center and lower bottom dead center the piston has more distance to move with each explosion. There may be fewer revs but more power with each rev which explains why diesel vehicles have less speed but can carry more load/cargo over longer distances.
  Engines vary in their torque output and torque is a key factor that is used to determine the horsepower of an engine. Two engines of the same horsepower can have different amounts of torque and at different RPMs and this is how the manufacturers intended through research, altering the dimensions of engines and the way they function.
  That is why two engines can have relatively the same rev limit (up to 8000/minute for example) but one engine can have two, three or four times the torque and power than the other. Its just about the knowledge of how to generate more rotational force on each power stroke.
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