| Half Shaft |
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| An articulating, rotating shaft used in independent-suspension systems that transmits power from the final drive unit (differential) to a power wheel. Used in independent rear suspension and front-whe |
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| Hand Crank |
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| A crank handle for manually starting internal combustion engines. Used till about 1930. Now obsolete.
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| Handling |
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| A general term covering all the aspects of a car`s behavior that are related to its directional control.
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| Heavy-duty Vehicle |
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| Vehicle (truck) weighing from 26,001 to 33,001 lbs. Also included off-highway trucks. |
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| Heel-and-Toe |
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| A performance-oriented technique of down-shifting while braking that requires the driver to use all three pedals of a manual-transmission car simultaneously. To perform a heel-and-toe downshift, the driver brakes with the toe of his right foot and: while continuing to brake: uses the heel or the side of the same foot to blip the throttle and raise engine rpm as he downshifts. The left foot operates the clutch pedal in the normal fashion. The sequence is as follows: brake with the right toe; depress the clutch with the left foot; shift to neutral; while continuing to brake, blip the throttle with the side or the heel of the right foot to raise rpm; shift to a lower gear; let the clutch out; release the brakes. The technique is difficult to master, but after practice it can be performed in less than a second. This process is best for smooth power flow and long transmission life. |
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| Heim Joint |
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| An extremely rigid articulating joint, commonly known as a ""spherical rod-end,"" used in any precision linkage. Heim joints are often used in the suspension links of race cars because they locate wheels very precisely |
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| Helical Gear |
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| A gear in which the teeth are cut at an angle to the shaft. The advantage is that there are usually two teeth meshing at all times, making for smoother and quieter operation. Helical Gear A type of gear in which the teeth are cut at a slanting angle to the gear`s circumference. A helical design produces an even, constant tooth loading in a gearset, thereby reducing noise.
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| Hemi |
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| A term used to describe any engine that has hemispherical combustion chambers in its cylinder head. Although a four-valve design is more efficient, a hemi head provides room for a pair of large valves and offers good breathing characteristics. Used in many sports and racing cars |
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| Hemi-Head |
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| A hemispherically shaped combustion chamber at the top of the engine cylinder. The hemispheric shape provides improved efficiency because the forces of the explosion are directed to the piston by the curved surface of the combustion chamber.
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| Horsepower (BHP) |
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| The unit for measuring the power output of an engine. Net horsepower or bhp (brake horsepower) and Kw (kilowatts) are the standard units. Higher horsepower increases vehicle top speed. Equal displacement (size) engines that rev higher often produce more power than lower revving engines, because more air and fuel is burned in a given time. A typical 3.0L 24V V-6 produces 190 bhp @ 6400 RPM. A lower revving 3.0L 12V V-6 produces 160 bhp @ 5000 RPM. The 24-valve V-6 makes 190 bhp because it can rev higher (and breathe better) than the similar 12-valve V-6. One horsepower is defined as lifting 33,000 pounds one foot per minute. One horsepower equals 550 foot-pounds per second, the power needed to lift 550 pounds one foot off the ground in one second: or one pound 550 feet up in the same time |
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| Hydraulic |
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| A mechanical operation based on incompressibility of liquids, generally oil and sometimes water, and their ability to offer resistance when being forced into a small cylinder or through an orifice, thereby transmitting an increase in applied force. Hydraulic brakes and clutches use this principle. |
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