Glossary of terms

AERODYNAMICS - The study of the behavior of the airflow as it passes around a moving object and the forces exerted by the air on the object. In car design the positive and negative lift of the airflow is studied in wind tunnels. Negative lift is preferred to press the vehicle closer to the ground. Car air resistance is also studied.

AUTOMATIC TRANSMISSION - A transmission that shifts its own gears according to the prevailing speed, load, and road condition. Also called automatic gearbox. Operation can be electrical or hydraulic.

BELT DRIVE - A system where the final drive from gearbox to wheels is by leather or rubber belts that are contained on pulleys. Today many of the engine-driven auxiliaries use belt drives.

BORE - The diameter of a gasoline or steam reciprocating engine cylinder. The displacement can be increased by increasing the diameter (reboring).

BRAKE HORSEPOWER - The measure of an engine's horsepower without the loss in power caused by the gearbox, generator, differential, water pump and other auxiliaries. The actual horsepower delivered to the driving wheels is less.

CAM - An eccentric (off-center) lobe or projection on a rotating shaft; used to transmit a motion at a predetermined time during the rotation of the shaft.

CAMSHAFT - A rotating shaft with a number of cams or eccentric lobes used to operate the engine valves, usually via pushrods and rocker arms.

CARBURETOR - A device through which air and fuel are atomized and drawn into the engine. It meters the proper proportions of fuel and air to form a combustible mixture and varies the ratio according to the engine operation.

CHAIN DRIVE - The driving of one shaft by another by means of a toothed wheel on each shaft, with the wheels connected by an endless chain with special links engaging the teeth.

CHASSIS - The basic-strength auto frame including the engine, suspension, wheels, brakes and drive train. A car without its body or coachwork. In monocoque or unit construction it is integral with the body.

CHOKE - A temporary restriction in a carburetor throat that reduces the flow of air and enriches the fuel-air mixture to aid in starting the engine.

CLUTCH - A friction device used to connect the engine to the drive train. Used when changing gear ratios during acceleration. Can connect or disconnect the engine and the drive train at driver's will.

COACHWORK - The automobile body: especially the comfort and luxury appointments as distinguished from the operational chassis.

COMBUSTION CHAMBER - The space remaining at the top of the cylinder when the piston is at the top dead center position. Where the fuel-air mixture begins to burn.

COMPRESSION - In internal-combustion reciprocating engines, the squeezing of the fuel-air mixture in the cylinder of a spark-ignition engine or the squeezing of the air in a diesel engine. Compression makes combustion more effective and increases engine efficiency.

COMPRESSION RATIO - The ratio of the cylinder volume with the piston at bottom dead center to the cylinder volume with the piston at top dead center.

CONNECTING ROD - The arm that connects the piston to the crankshaft and converts the reciprocating motion into rotary motion.

CONVERTIBLE - Any car with a folding roof. Term used in U.S. since the 1930s. In the 1950s, the "hardtop convertible" was developed to look like a convertible but had a fixed roof that did not fold. Also called a drophead coupé.

CONVERTIBLE SEDAN - The conventional body has 4 doors and a folding top with roll-up windows.

COUPE - Originally meant a vehicle "cut" by a glass partition behind the front seats that enabled the rear passengers to ride enclosed and the driver exposed. Today, a two-to-five-seater with smaller interior than a sedan. Usually a sporty type.

COWL - That part of a car's body between the engine compartment and the driver.

CRANKCASE - A pan or box that encloses the bottom of the engine, supports the crankshaft, and contains the oil for the engine.

CRANKSHAFT - The main shaft of an engine with a U-shaped offset at each cylinder to which the connecting rod is attached. It delivers rotary motion taken from the reciprocating pistons and connecting rods.

CUBIC CAPACITY - The volume of the cylinder between the piston top dead center and bottom dead center. Expressed in cubic centimeters or cubic inches.

CUBIC CENTIMETER (cc) - European, metric, and competition measure of engine displacement: 1,000 cc = 1 liter, which equals about 61 cubic inches.

CUBIC INCH (cu. in.) - U.S. measure of engine displacement: 1 cubic inch = 16.387 cc.

CUSTOM CAR - An automobile that has been restyled, or an all-new body fitted on an existing chassis.

CYCLE-CAR - A term used to describe the very light production autos made prior to 1922. Usually made from motorcycle parts and generally powered by single- or twin-cylinder engines. Disappeared when genuine light cars appeared.

CYLINDER - The hollow tubular cavity in the cylinder block in which the piston travels and in which combustion takes place.

CYLINDER HEAD - The detachable part of the top of the cylinder block that contains the spark plugs and valves. It seals the cylinder and forms the top of the combustion chamber.

DIESEL ENGINE - An internal-combustion engine in which the fuel is injected into the cylinder near the end of the compression stroke and is ignited by the heat of the compressed air in the cylinder. No spark plug or carburetor is needed.

DIFFERENTIAL GEARS - The gears that convey engine power to the driving axles and are arranged so as to permit the rear wheels to turn at different speeds as required when the vehicle is negotiating a turn.

DISC BRAKE - A type of brake in which two friction pads grip a steel disc that is attached to the wheel, with one pad on each side. Used on race cars, sports cars, and better passenger cars.

DISTRIBUTOR - The moving part of the internal-combustion engine ignition system that directs the high-voltage current from the coil to the spark plugs in the proper firing order.

DRIVE TRAIN - That combination of gears, clutches, shafts, etc., that transmits the engine power to the wheels.

ELECTRICAL SYSTEM - In electric ignition internal-combustion engines, those components required to convert the electricity produced by the generator into a high-voltage spark for the plugs. Includes: generator or alternator, points, condenser, coil, distributor and spark plugs plus wiring.

ENGINE TYPES - F-Head Side exhaust valve and overhead inlet valve. L-Head Both valves on one side of the cylinder. T-Head Exhaust valve on one side and inlet valve on the other side of the cylinder. (Twin-camshafts). I-Head Both valves located directly over the piston. Also called valve--in-head or overhead valve engine. SOHC Single overhead camshaft. DOHC Double overhead camshafts.

EPICYCLIC GEARBOX - A form of gear used by Benz in which small pinions revolve around a central or sun gear and mesh with an outer ring gear called the annulus. Type used in the Ford Model T. Also called planetary gears, sun-and-planet gears.

EXHAUST - The system of exhausting the burned gases from an internal-combustion engine consisting of piping or tubing, silencers, and, at times, resonators.

FASTBACK - A car that has an unbroken curved line from the top of the roof to the rear bumper as opposed to a drop in the line for a near-vertical rear window. In a fastback design the rear window slope follows the unbroken roof line and is often at less than a 45 degree angle.

FIBERGLASS - A very tough and durable plastic material with fibers running through the plastic. Used for race car bodies, many sports car bodies, and also enjoys considerable acceptance for passenger car bodies.

FLYWHEEL - A large, heavy iron or steel disc attached to the rear of an engine crankshaft in order to provide sufficient centrifugal force to smooth the power impulses from the cylinders.

FOUR-STROKE CYCLE - An internal-combustion engine that requires two revolutions per cylinder or four piston strokes to achieve a power stroke: internal stroke, compression stroke, power stroke, exhaust stroke. More efficient than the two-stroke-cycle engine. Also called Otto cycle.

FRAME - A bridge-like, structural base of a car that supports and positions the body and major mechanical items.

FUEL INJECTION - On internal-combustion engines, a system that injects a precisely measured amount of fuel into the cylinder at exactly the right moment. Dispenses with the carburetor and increases engine efficiency.

GAS TURBINE - An internal-combustion rotating engine with one main moving part: the rotor with pinwheel-like blades attached. Air is compressed by the first rows of blades and delivered to the combustion chambers, from which the exhaust is directed to pass the remaining blades and to generate the power. Power is extremely smooth due to the absence of explosions and reciprocating parts.

GEARS - Wheels with meshing teeth to transmit power between rotating shafts. When the gear wheels are of different sizes, a change in speed ratio occurs. Gears are made of hard steel.

G.T./ GRAND TOURING - From the Italian Gran Turismo. A car combining sedan and sports car features in which engineering is the dominant feature. Combines excellent road handling qualities with relative comfort. Made in two- and four-seaters with the rear seats always cramped.

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HALF SHAFT - A rotating shaft that transmits power from the final drive unit (differential) to a power wheel. Used in independent rear suspension and front-wheel drive. Two are required; one for each side.

HAND CRANK - A crank handle for manually starting internal combustion engines. Used till about 1930. Now obsolete.

HELICAL GEAR - 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.

HEMI - Slang term for an engine with hemispherical combustion chambers which allow for larger and less shrouded valves. Used in many sports and racing cars.

HEMI-HEAD - 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.

HOOD - The removable or lift-up part of an auto body that covers the engine and allows access to it. (Bonnet in U.K.)

HORSEPOWER - The unit for measuring the power output of an engine. One horsepower is defined as lifting 33,000 pounds one foot per minute.

HOT ROD - A production auto that has been modified by the owner for outstanding speed and acceleration through extensive changes to the engine, chassis, and body.

HYDRAULIC - 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.

HYDRAULIC VALVE LIFTER - Valve lifter using hydraulic oil pressure to operate and capable of maintaining zero clearance between metal parts. Thus, valve noise and wear are considerably reduced as are the periodic valve adjustments.

HYPOID GEARS - A type of differential final drive using a spiral bevel gear on the drive shaft, allowing it to be located below the center of the ring gear on the axle. This makes possible a lower floor in the car.

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INDEPENDENT SUSPENSION - Suspension in which each wheel is sprung individually so that any disturbance on the wheel has no effect on the opposite wheel.

INLINE ENGINE - An engine having the cylinders in a straight line, one after the other. Also called a "straight" engine.

INTERNAL-COMBUSTION ENGINE - Any engine, either reciprocating or rotary, in which the fuel is consumed in the interior of the engine rather than outside of the engine.

KNOCK-OFF A single wing nut for fastening a wheel to the hub. Easily removed and replaced, it is struck (knocked off) with a mallet on the wings.

LACQUER A fast-drying pyroxylin paint often used to finish automobile bodies.

LAMINATED WINDSHIELD A windshield consisting of a thin layer of rubbery plastic sandwiched between two sheets of glass. When struck by the head in an accident, it bows out without puncturing, and the plastic holds the glass to prevent it from splintering.

LEAF SPRINGS A number of slightly curved, flexible steel plates of varying lengths, mounted one atop the other. The ends are attached to the chassis, and the middle is fixed to the axle. Also called semi-elliptic springs.

LIMITED SLIP DIFFERENTIAL A differential that uses cone or disc clutches to lock the two separate axle shafts. This forces both driving wheels to transmit the same drive torque regardless of the traction available. It still allows differential action under normal driving conditions but improves traction in mud and snow.

LIMOUSINE A closed, chauffeur-driven automobile in which the driver is separated from the passengers by a glass partition.

LIVE AXLE An axle that transmits power either by separate half shafts or by side chains, as opposed to a dead axle.

LOUVER A slatted air intake or air outlet. Slats used to capture and control the air flow.

MANUAL TRANSMISSION A mechanism in the drive train with gears to vary the power and torque delivered to the driven wheels. It consists of a lever that the driver operates in conjunction with the clutch to change from one gear to another.

NORMALLY ASPIRATED - An engine that intakes air or "breathes" without the assistance of a supercharger or turbocharger.

OIL PUMP - An engine-driven pump that delivers oil, under pressure, to the engine's moving parts.

OIL RING - The lowermost piston ring that scrapes off excess oil from the cylinder walls and returns it to the oil pan via vents in the ring and piston.

OVERDRIVE - A small auxiliary gearbox that provides an additional gear ratio. It causes the drive shaft to turn faster than the engine crankshaft or "overdrive" it. It is engaged manually when under way and reduces fuel consumption

PINION - A small diameter gear with a small number of teeth designed to mesh with a much larger gear wheel or a toothed rod (rack). Used in rack-and-pinion steering and for speed reduction with an increase in power.

PISTON - A partly hollow, cylindrical metal engine part that is closed at one end and fits into the engine cylinder. Connected to the crankshaft via the connecting rod and usually fitted with rings to seal it in the cylinder.

PNEUMATIC TIRE - A circular tube of rubber or synthetic rubber and fabric, and sometimes also steel, attached to the rim of the car's wheel, having resilience due to its containing air under pressure.

PRE-SELECTOR GEARBOX - An arrangement that enables the driver to select a gear speed before he needs it and then depress the clutch pedal when he desires to use the selected gear.

PROTOTYPE - The test model of a new car design that is intended to be produced in quantity.

PUSHROD - A metal rod connecting the valve lifter or camshaft with the valve rocker arm on overhead-valve engines.

RACK-AND-PINION STEERING - A steering system having a pinion gear at the lower end of the steering column that engages a rack or a toothed rod that connects to the wheel steering arms.

RADIAL PLY - A tire in which the fabric cords run radially in a line from the wheel hub or straight out from the bead or around the tubular shape of the tire. Annular belts of fabric or steel mesh add rigidity. Advantages of this design are: more flexible side walls with a relatively stiff tread area and a larger and more consistent footprint on the road under all driving conditions.

RECIPROCATING - Motion of an object between two limiting positions. Applied to piston engines because of the limited up and down motion of the pistons.

RING GEAR - One of the gears in the rear axle that transmits power to the differential from the drive shaft.

ROCKER ARM - A pivoted lever that transmits the action of the pushrod to the valve stem. (Pushrod upward action is converted to downward push on the valve stem.)

RUNNING BOARD - A long flat board under the car doors that acts as a footstep for the passengers.

S.A.E. Society of Automotive Engineers. - A group known for publishing research papers and defining various standards of measurement.

SEALED BEAM - A one-piece, hermetically sealed headlight in which the filament is an integral part of the unit, and the lens itself is the bulb.

SEDAN - A closed car for four or more passengers with either two or four doors. (Called saloon in U.K.)

SELECTIVE TRANSMISSION - The conventional manual transmission of today in which any gear may be selected at will as opposed to the very early progressive transmission in which the gears had to be selected in order.

SHOCK ABSORBERS - A term used for what are really dampers. Fittings used to absorb the energy that the wheels convey to the springs. The dampers keep the springs from continuously rebounding. The majority of shock absorbers are hydraulic.

SLEEVE VALVE - Consists of metal sleeves located between the piston and cylinder wall. When moved up and down, holes in the sleeves coincide with inlet and exhaust parts to provide passage for the gases at the right time.

SPARK PLUG - A device inserted into the combustion chamber of a cylinder on an internal-combustion engine that provides the electrical gap across which the high-tension voltage jumps. This creates a spark that ignites the compressed fuel-air mixture.

STROKE - The back-and-forth motion of the piston. The length of the motion of the piston from top dead center to bottom dead center.

SUPERCHARGER - An air compressor fitted to an internal combustion engine to force the fuel-air mixture into the cylinders at a pressure greater than that of the atmosphere. Boosts the power of the engine.

SUSPENSION - The assembly of springs, shock absorbers, torsion bars, joints, arms, etc., that cushions the shock of bumps on the road and serves to keep the wheels in constant contact with the road, thereby improving control and traction.

SWING AXLE - Type of independent rear suspension using half shafts that have universal joints only at their inboard ends on both sides of the differential. This causes a camber angle change of the wheel with up-and-down wheel movements.

TACHOMETER - An instrument that indicates the number of revolutions per minute at which the engine is turning.

TORSION BAR - A rod in the suspension system that, when twisted from a grip at one end, functions like a spring.

TRANSMISSION - The gear-changing or gear-shifting system through which engine power is transferred to the wheels. The purpose of gear-changing is to keep maximum engine power applied to the wheels at all times for all conditions, from start-up to high speeds.

TREAD - Width of a car measured from the center line of the wheels. Sometimes called the track. Also the pattern on the surface of a tire.

TURBOCHARGER - A supercharging device driven by exhaust gases from the engine.

TWO-STROKE CYCLE - An internal-combustion engine that requires only one revolution per cylinder or two piston strokes (up and down) to achieve a power stroke. Rarely used in automobiles.

VALVE Device that opens and closes the combustion chamber of an internal-combustion engine to admit the fuel-air mixture or exhaust the gases.

VEE ENGINE An engine with cylinders arranged in two rows at an angle to the common crankshaft. Has a "V" shape when viewed from the front.

WHEELBASE The distance between the centers of the front and rear wheel axles as viewed from the side of the vehicle.