Underdrive pulleys

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Underdrive means to slow the rate of rotation in a system. Underdrive is achieved by either making te crank/main (drive) pulley smaller or the accessory (driven) pulley larger than the original diameter pulleys.

Underdrive pulleys increase engine output by reducing the draw of the engine's accessories by slowing them down and reducing the HP they use. Horsepower gains from underdrive pulleys can vary by vehicle, engine, number of accessories and the amount of underdrive (Improvements of up to 5-15 HP at the wheels have been seen). Additional and significant performance improvements can be seen by reducing the weight of the pulley versus the original pulley. Gains can range from 3-6 HP per pound of weight reduced.

Horsepower unit of power

Horsepower (hp) is a unit of measurement of power, or the rate at which work is done. There are many different standards and types of horsepower. Two common definitions being used today are the mechanical horsepower, which is about 745.7 watts, and the metric horsepower, which is approximately 735.5 watts.

Poorly engineered underdrive pulleys can cause unwanted side effects; this is due to not spinning the alternator, power steering, and/or air conditioning fast enough. This leads to low alternator voltage, weak/no power steering assist, and weak/no air conditioning effectiveness, especially at idle/low RPM. The most commonly seen result is lighting may dim, or the stereo may cut out. Too much underdrive for a race car is not much of a concern due to the high RPMs they run at, but for daily driven vehicles it can lead to a dead battery if too much time is spent at idle or low RPM. Additionally, an underdrive pulley will not reduce the power consumed by the alternator, as the alternator's load is automatically adjusted by its control circuit to match the electrical load regardless of input speed.

Air conditioning Process of altering the properties of air to more favourable conditions

Air conditioning is the process of removing heat and moisture from the interior of an occupied space, to improve the comfort of occupants. Air conditioning can be used in both domestic and commercial environments. This process is most commonly used to achieve a more comfortable interior environment, typically for humans and other animals; however, air conditioning is also used to cool/dehumidify rooms filled with heat-producing electronic devices, such as computer servers, power amplifiers, and even to display and store some delicate products, such as artwork.

Changing the original crankshaft pulley can also have negative effects if the replacement pulley is not manufactured properly. A crankshaft or accessory pulley not machined or balanced properly can cause severe damage leading to thousands of dollars in repairs.

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