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PCM
Pulse Code Modulation. A digitally encoded radio transmission that uses FM as a carrier method but is far superior to analog FM or AM as it is virtually glitch free.
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Phillips Screwdriver
A four-pointed screw driver. Most common type of screw head in the world.
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Pilot Shaft
A shaft with a hexagonal head with a slot cut rotationally and a large female screw hole on one end and a smaller female screw hole on the other end. The flywheel is then pressed between the engine's drive shaft collet and this pilot shaft where it is held perfectly centered and snuggly secured. The rotational slot is intended as a backing groove for the clutch springs and the smaller female threaded hole on the opposite end is intended to secure the clutch bell assembly onto the end of this pilot shaft. All in all the pilot shaft's responsibility is to provide a centerpiece for the clutch assembly and to secure the flywheel against the tapered collet.
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Piston
Metal cylinder typically made of aluminum alloy that acts as the compression chamber plunger in a combustion engine.
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Pitch
Number of teeth per inch on any gear. Generally, the lower the number, the larger the teeth; the higher, the smaller.
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Polarity
The natural opposition of two equal forces as in electrical current (DC, specifically) or as in a magnet. Electrical current is identified by its polarity of plus (positive) and negative (ground).
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Power Train
The mechanisms that transfer power from the engine to the wheels, including drive shafts, gears, pulleys, belts, differentials, universal drive shafts, dogbones, transmissions (gearboxes), outdrives, etc.
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Preload
The load a spring has on it when it is installed in its shock assembly (coil-over shock is a good example) at it's fully extended position and with no external load. This is commonly done to prevent spring depression from normal weight of vehicle being exerted. By preloading, you can keep suspension stiff and rigid until it comes in contact with a force great enough to overcome the preload factor.
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Pre-Race
Any event that takes place before the actual race. This can include concours events, practice and even qualifiers themselves.
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Programmable
Usually refers to a radio transmitter, but more recently applies to servos. Simply means that user can specify desired parameters that are usually stored electronically.
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