Torque is twisting force. A homeowner turning a screw into a board with a screwdriver is generating torque. Torque turns the driveshaft leading into the gearbox of a car or truck, and it affects how well the vehicle does in everyday driving. It's measured in foot-pounds, or the amount of force necessary to lift a 1-pound weight 1 foot in the air.
The engine turns the driveshaft with a measurable amount of force and does it several thousand times a minute. An engine can go very slow or very fast through a range of speed called the power band, which is usually from less than a 1,000 rpm to more than 6,000 rpm in everyday driving.
The torque an engine delivers changes through the power band due to the design of the engine. It might produce 200 foot-pounds when the engine is running at 1,500 rpm and 400 foot-pounds when the engine hits 3,000 rpm. Horsepower is the product of the torque the engine can deliver and the number of times each minute that it can deliver it. An engine will usually measure the greatest torque at the lower part of the power band and the most horsepower at the upper end of the power band. As the engine increases in speed, it delivers less torque, but delivers it more often. For example, an engine might produce 400 foot-pounds of torque at 3,000 rpm and only 300 foot-pounds at 6,000 rpm, but it's delivering it twice as often.
Small sports car engines often have low torque in the lower two-thirds of the power band. The engine must be kept at high speed to develop all of the force available to move the car along. However, in daily driving, the engine rarely goes past the middle of the power band so an engine that has a high torque production early in the power band is more comfortable to drive.
A truck needs a lot of torque when it's towing a boat on the freeway. The engine uses more fuel the faster it goes, and it wears out sooner. A truck that can comfortably travel at 70 miles an hour with the engine turning over at 3,500 rpm will use less fuel than one that has to keep the engine rotating at 5,000 rpm to stay at the same speed. Also, a driver will find it easier to pass slower vehicles if he can simply press on the accelerator and go faster, instead of changing to a lower gear to do the same thing.
General Motors introduced the Generation VI 454 engine in 1996 for use in its truck line. GM made it for five years until replacing it with the Vortec 8100. The stock 454 engine produced 290 horsepower at 4,000 rpm and 410 foot-pounds of torque at 3,200 rpm. For its April 2007 issue, "Chevy High Performance" magazine enhanced a Generation VI 454 engine with performance parts and reported getting 541 foot-pounds of torque at 4,100 rpm.