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| Decamber | To make the wheel camber more negative. |
| Deck | Generally the rear most upper body panel of a car, but not present in all cars. |
| Deck Lid | The access door into the volume (often "trunk) beneath a deck. |
| Differential | A gear assembly, physically separate from the transmission, whose purpose is to reduce the rotational velocity transmitted from the engine/ gearbox, while providing a division of driving force to two (2) wheels. |
| Differential Housing | The housing in which the differential (final drive) gears are mounted. |
| Disc Brake | A braking system which relies on the friction between a suitable material in the form of a "pad' and a rotating disc to supply the braking force at a wheel. |
| Discriminator Valve | A check valve designed to install on the vent line of a fuel cell, allowing vapors to vent while retaining liquid. |
| Dish | A concave piston crown. |
| Displacement (Engine) | Reciprocating engine: the swept volume of one (1) cylinder times the number of cylinders. Rotary engine: the difference between the largest and smallest volumes of the working chamber, times the number of lobes, times the number of rotors. |
| Distributor Cap | An ignition system distributor component which contains the high voltage distribution contacts and means for securing the high voltage wires. |
| Dome | A convex piston crown. |
| Door Panel | The inner shell of a door which normally supports the trim. |
| Dowel | A tubular or cylindrical pin, the sole purpose of which is to make positive location of two assembled components possible. |
| Drive Belt | A continuous flexible reinforced elastomer band which provides the driving force for engine accessories, when attached by pulley to a rotating part of the engine, such as the crankshaft. |
| Drive Shaft | The mechanical drive train coupling between transmission and differential, which may allow an angular displacement of the driving and driven axes by the use of universal, constant velocity, or flex joints. |
| Drive Train | Those components in a car which produce and convey the driving power to the ground, and the housings containing these parts. |
| Dry Break Coupling | An attachment to an on-board fuel cell/tank filler neck/hose which is designed to prevent the spillage of fuel during refueling operations. |
| Dry Sump | An engine lubrication system in which the residual lubricant is pumped I
external storage tank by a "scavenge pump," and an additional pump or pumps return a supply of pressurized lubricant to the engine from the storage tank. |
| Dry Tire | A race tire, often with grooveless tread, intended strictly for use in competition under dry conditions. |
| Dryer (AC) | A component of an automotive air conditioning system which is intended to remove water from the refrigerant. |
| Duct/Ducting | A tube or passage for conveying a material, usually air |
| Dust Shield | A cover intended to protect disc brake components from mud, dirt, etc. |
| Eccentric Shaft | The analog of a crankshaft in a rotary engine, the shaft driven by the actions of the rotor |
| EGR Valve | An engine pollution control device which channels a portion of the I gases back into the combustion regions of the engine. |
| End Plate | An air control panel mounted at each end and perpendicular to a wing, intended to maximize the efficiency of the wing by preventing spillage of flowing air at the ends. |
| Engine | The primary power plant of a car, including all physically attached ancillary components necessary for power production. |
| Engine Air Box | An induction system attachment, generally part of the bodywork, which ducts air from an opening protruding into the airstream to the induction system intake(s). |
| Engine Case | See rotor housing and/or block. |
| Engine Compartment | The loosely defined volume, nominally enclosed by panels on top and sides, which is the normal location of the engine in a car |
| Engine Steady Bar (Torque suppressor) |
A constraining beam or rod intended to resist the tendency of an engine to rotate on its mounts in reaction to torque forces. |
| Epitrocoidal Curve | The contour of the interior surface of a rotary engine rotor housing, which, with the rotor, determines the volume of the working chambers at any point in the rotation of the rotor |
| Evaporator (AC) | That portion of an automotive air conditioning system in which the transition from liquid phase to vapor phase occurs. |
| Exhaust Pipe | A duct of unspecified dimensions, whose function is to convey exhaust products toward the rear of a car and away from the driver |
| Exhaust Port | The duct within a cylinder head or rotor housing through which the exhaust gases pass from the exhaust valve(s) to the outer flange of the head. |
| Exhaust System | A passive system, whose components serve to convey the exhaust of an engine past the driver and away from the car. |
| Expansion Tank | A container, often operating at system pressures, which is designed to contain engine coolant on expansion at operating temperatures. |
| Extension | An external modification resulting in more material on the outside of the component than originally existed. |
| Fairing | A covering intended to divert airflow in a specific region of a car, to reduce air drag. |
| Fan | A rotating bladed device intended to provide a cooling flow of air to a heat exchanger. |
| Fan Belt | A flexible drive belt which is used to drive a water radiator cooling fan, and, often simultaneously, furnish drive to one (1) or more other rotating attachments to the engine. |
| Fender | The body panel covering a road wheel assembly. |
| Fender Flare | An attachment to an existing fender which extends the fender outward so as to more completely cover the tire within. |
| Fender Skirt | A removable fender extension which partially closes the wheel opening, smoothing the air flow in this region. |
| Filler Cap | A closure which prevents the loss of fuel from the filler neck/hose when the car is in use, but which may be removed for refueling. |
| Filler Neck/Hose | The attachment to a fuel cell/tank through which fuel is supplied from a
source external to the car |
| Final Drive Housing | See Rear Axle Housing. |
| Final Drive Ratio | The ratio of input to output shaft motions in a final drive or differential. |
| Fire Extinguisher | An on-board container of specified capacity charged with approved fire extinguishing material which provides the driver or others with the capability to control small fires. See GCR Section 12. |
| Fire System | An on-board fire extinguishing system designed to be activated in the event of fire, whose purpose is to extinguish or retard the fire, thus providing a measure of protection for driver and car See GOR Section 12. |
| Firewall | A vertical (plus or minus ten (10) degrees) metal panel separating and protecting the driver/passenger compartment from the engine compartment, preventing the passage of flame and debris. Metal ducts may penetrate the firewall, but must begin and end outside of the driver/passenger ~ compartment. No intakes are allowed in the firewall. |
| Firing Order | The order in which the cylinders in a reciprocating engine produce power under normal conditions. |
| Flare (Verb) | 1. To extend by extrusion or attachment a fender so as to more completely cover the tire mounted within (Noun) - 2. Extruded end of a pipe or tube. |
| Flat Bottom | A race car constwction in which the underside of the car is nominally flat and contains no "ground effects" shaping or ducting. |
| Flex Joint | A coupling designed to fulfill the function of a universal joint, but employing flexible materials to achieve changes in the drive axis. |
| Float | A carburetor component which, with an associated valve, controls the fuel level in the reservoir supplying the carburetor jet(s). |
| Float Chamber | The carburetor component which contains the reservoir of fuel I supplying the jet(s). |
| Float Valve | The shutoff valve actuated by a carburetor float, which controls the maximum level of the fuel in the float chamber |
| Floor Pan | The section(s) of a car normally used as a supporting platform for 5 seats
and to physically separate the interior (cockpit) area from the underside of the car |
| Fluid | Any material which readily flows at the specified temperature, e.g., liquids and gases at room temperature. |
| Flywheel | An engine attachment whose normal functions are to provide a gear appropriate for starter engagement, to provide a friction drive surface and attachment points for a clutch pressure plate, and to smooth the flow of power |
| Frame | The minimal configuration of a car necessary to contain all running gear and to provide support for the body. Not present on "f rameless" or "unibody' cars. |
| Fuel | The chemical mixture which, when mixed with air, is burned in an engine to produce power |
| Fuel Cell | A crash-resistant container for the on-board fuel supply of a car |
| Fuel Distribution Unit | A fuel injection induction system component which accomplishes the distribution of fuel to the injection nozzles. |
| Fuel Injection | A system, including mechanical and/or electrical components, whose function is to provide fuel, via pressurized nozzles, to the engine in lieu of carburetion. |
| Fuel Line | A hose or tube which conveys fuel from one point to another |
| Fuel Metering Unit | A component of a fuel injection system which, under external control, determines the quantity of fuel supplied to the engine at any given time. |
| Fuel Pickup | The attachment to a fuel tank or fuel cell at which point the supply line(s) leading to the fuel pump(s) are attached. |
| Fuel Pump | A pump, mechanical or electromechanical, whose function is to cause the transport of fuel from the fuel cell or tank to the induction system. |
| Fuel Tank | A conventional OEM container, not of the safety fuel cell type, for the on-board fuel supply of a car |
| Gas Cap | See Filler Cap. |
| Gasket | A sealing component of unspecified composition which is intended to prevent the leakage of a fluid (air, water oil, etc.) at the interface between two demountable assemblies. |
| Gauges | Mechanical or electronic readouts of automotive parameters. |
| Gear | A toothed drive train component used, in mesh with another gear, for the transmission of rotational force. |
| Generator | An engine-driven attachment which produces direct current to replenish an on-board storage battery. |
| Girdle | An engine component whose purpose is the structural reinforcement of the bottom end of an engine block by the replacement of the main bearing caps with a continuous block of material containing equivalent bearing mountings. |
| Grille | The decorative covering for the grille opening. |
| Grille Opening | The opening in the front of a car, through which cooling air is ducted to the radiator(s), and in some cases, to other accessories, or to the engine. |
| Ground Effects | A temi for a car design in which airflow produces a significant pressure differential between the upper and lower portions of the body/ chassis, creating downforce on the assembly. |
| Gudgeon Pin | English term for piston wrist pin. |
| Gusset | A brace generally formed by attaching, by welding, a plate at or near the junction of two structural beams or tubes, providing reinforcement particularly in the plane including the tubes and the plate. |
| H.D. | Heavy duty. |
| H.T. | High tension. English term for spark plug voltage in regard to ignition components. |
| Hand Brake | A braking system component causing a braking action on one (1) or mare wheels, or on another pad of the drive train, which may be actuated and locked in the engaged position by the driver |
| Deck Height | The distance between the top of the piston at its outer edge and the machined surface which forms the head/block interface of the block. |
| Engine Mount | A passive mechanical coupling used to support the weight of an engine at its attachment points to the structure of a car. |
| Hardtop | A removable rigid substitute for a convertible or roadster top. |
| Hatchback | A hinged body component containing the rear window which, in the open position, gives access to the interior of a car from the rear |
| Head Rest | See Head Restraint. |
| Head Restraint | A cushioned, fixed restraining object intended to protect the driver |
| Header | A multibranch exhaust system assembly, whose function is to convey the exhaust products from more than one cylinder to one or more exhaust pipes. |
| Header Tank | A component of an engine cooling system, generally at the top or above the radiator, which is often used as the filling point for the system. |
| Headlight Cover | A protective cover for headlight(s) which is part of the original configuration of the body design. |
| Heat Riser Tube | An attachment to an induction system which provides a source of warmed air, generally from the exhaust system, as an aid to cold running. |
| Heat Sink | A part of a system used to convey and dissipate heat from another part of the system. |
| Helicail | A commercial repair for internal threads. |
| Homalagation | A system whereby the manufacturer/competitor certifies that a Formula or Sports Racing car, as produced, complies with all of the applicable specifications. |
| Hood | The panel or assembly of panels which cover the engine compartment. |
| Horn | The audible signaling device with which highway cars are equipped. |
| Hat Terminal | The terminal of a storage battery which is not connected to the frame or chassis of the car. |
| Hub | A component to which a road wheel is attached, which provides support for the wheel, and has the capability, via attached internal bearings to rotate on a fixed shaft. |
| Hub Caps | Decorative removable attachments to the central area of road wheels. |
| Hub Carrier | A suspension component which provides the means for mounting a rotating wheel hub, and for attachment of suspension components and stabilizers. |
| Idler Shaft | A shaft which rotates, or supports another component which rotates, without itself transmitting the rotational force. |
| Ignition System | A system which converts on-board storage battery supply voltage into a timed sequence of high voltage pulses suitable for igniting engine combustion mixtures in a controlled manner. |
| Independent Suspension | A suspension system in which either wheel on the referenced end of the car can undergo its normal vertical motions without directly influencing the motions of the other wheel. |
| Induction System | Those engine components directly associated with the creation and conveyance of the combustible mixture, and any functional associated attachments thereto. |
| Injection Nozzle | The fuel induction system component through which fuel is forced under pressure to form a combustible mixture with air |
| Inlet Port | The cylinder head duct leading to intake valve(s). |
| Insert (Strut) | The replaceable portion of a suspension strut, basically a tubular shock absorber with the necessary fastening element(s) for the upper strut mounting point. |
| Instrument | An indicator or readout which, when active, contains information about some aspect of car operation for driver reference. |
| Instrument Panel | A panel, located within the cockpit of a car, and in a position convenient for drivervisibility, which may provide a mounting area for various gauges and controls. |
| Intake | An opening through which fluid/air enters an enclosure. |
| Intercooler | A heat exchanger associated with a turbocharging or super-charging system, which is intended to reduce the temperature of the incoming air or air/fuel mixture, and is located in ducting between the turbo/super-charger and the engine. |
| IR | Individual runners. (No balance pipe, no plenum) |
| Jack Points | Locations on the underside of a car suitable for the application of a lifting jack. |
| Jack Shaft | A shaft which transfers a driving force from one element of an engine to another, such as the drive for an oil pump and/or distributor, taken from an overhead camshaft. |
| Jet | A carburetor aperture component which is used to meter air and/or fuel flowing into the mixing region of the carburetor by presenting restriction to the flow. |
| Kill Switch | See Master Switch. |
| L.T. | Low tension. English term for battery voltage in regard to ignition components. |
| Limited Slip Differential | A differential which is designed in such a way as to overcome the normal action of a differential to apply most of the available torque to the least loaded wheel, and instead to apply a significant portion of the torque to the most loaded wheel. |
| Linkage | A link or system of links (cables, rods, etc.) which convey a mechanical force from one location to another |
| Lip-Type Rear Spoiler | A directly attached aerodynamic device which generates downforce from the action of air flowing over a single surface, creating a turbulent depression away from the direction of motion. |
| Lobe Center | The angular position of a camshaft, defined as that position in the rotation at which the lift of an associated tappet will be greatest. |
| Locked Differential | A variation of the limited slip differential in which no relative slippage of the two driven wheels is permitted under any conditions. |
| Lubricant | A substance which, when interposed between components moving with respect
to each other, reduces friction and promotes durability. (see 17.36) |
| Luggage Compartment | The region within the bodywork of a car which is designated as being intended for the carrying of luggage. |
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