half-shaft: an articulating, rotating shaft used in independent-suspension systems to transmit power from a differential to a wheel.
handling: a general term covering all the aspects of a car's behavior that are related to its directional control.
heel-and-toe: 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.
heim joint: 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.
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.
hemi: 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.
horsepower: the common unit of measurement of an engine's power. 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.
Hotchkiss suspension: a live-axle rear suspension in which leaf springs handle both the axle's springing and its location.
hydraulic lifter: a valve lifter that, using simple valving and the engine's oil pressure, can adjust its length slightly: thereby maintaining zero clearance in the valvetrain. Hydraulic lifters reduce valvetrain noise and are maintenance-free.