Air Bag: The air bag, also known as a Supplemental Inflatable Restraint System, is a passive safety device, supplemental to safety belts, that inflates to provide a cushion to absorb impact forces during moderate to severe frontal collisions. This system can help to lessen the chance of contact with the steering wheel, instrument panel and windshield. The air bag is actuated automatically by sensors located in the front of the vehicle. To maximize effectiveness, seat and shoulder belts must always be used in conjunction with this system.
Airfoil: An aerodynamic device designed to improve traction by increasing the downforce on the car. The use of airfoils (also called spoliers or wings) increases the cornering capability and improves stability at speed, but often at the expense of additional aerodynamic drag.
Air Injection: A system that injects air into the exhaust ports of the engine for combustion of unburned hydrocarbons in the exhaust gases, thus producing “cleaner” exhaust emissions.
Alignment: Generally refers to wheel alignment, which is the proper adjustment of the car’s front and rear suspension for camber, toe, caster and ride height.
A-Pillar: In the side view, the foremost roof support of a vehicle, located in most instances between the outer edge of the windshield and the leading edge of the front door upper. Also known as an A-Post.
Alloy Wheels: A generic term used to describe any non-steel road wheel. The most common alloy wheels are cast aluminum. Technically, an alloy is a mixture of two or more metals. These wheels are known for their light weight and strength.
All-Wheel Drive: Often confused with Four-Wheel Drive (4WD), this drive system features four, full-time active drive wheels to reduce wheel slippage and provide greater driver control over the vehicle. All-Wheel Drive automatically splits engine torque between the front and rear wheels as needed, improving on-road traction in unfavorable road conditions. Unlike Four-Wheel Drive, All-Wheel Drive is an on-road system and is not designed for off-road use. AWD does not require the driver to actively engage the system. It is operational at all times, and requires no switches, lights or visor instructions for system operation.
Anti-Lock Brake System (ABS): On a vehicle equipped with Anti-Lock Brakes, the wheels are equipped with speed sensors. When a sensor determines that a wheel is decelerating so rapidly that lockup may occur, the electro-Hydraulic Control Unit (EHCU) is activated. The EHCU then modulates the brake pressure in the appropriate brake lines by means of the solenoid-operated valves. This is intended to prevent wheel lockup and help the vehicle maintain directional stability during potentially hazardous braking situations. (See also: Rear-Wheel Anti-Lock and Four-Wheel Anti-Lock.)
Automatic Locking Front Hubs: Found in some four-wheel drive vehicles, this allows the driver to engage, or “lock,” the front axle hubs without leaving the vehicle.
Axle Ratio: The ratio between the rotational speed (RPM) of the drive shaft and that of the driven wheel. Gear reduction in final drive is determined by dividing the number of teeth on the ring gear by the number of teeth on the pinion gear.
B-Pillar: The roof support between a vehicle’s front door window and rear side window, if there is one.
Balance Shaft: A shaft designed so that, as it turns, it counter rotates the rotational direction of the engine crankshaft in a manner that reduces or cancels out some of the vibration produced by the engine.
Ball Joint: A flexible joint consisting of a ball within a socket. Ball joints act as pivots which allow turning of the front wheels and compensate for changes in the wheel and steering geometries that occur while driving.
Base Coat/Clear Coat: A paint system that adds a final clear-coat paint layer over primer and color coats to provide a deep, “wet-look” shine that resists fading.
Belted Radial Tires: A reinforcing bank, normally textile, fiberglass or steel, running around the circumference of a tire and strengthening the tread area. The most common type of tire available today.
Bias-Ply Tires: A type of tire in which the plies or layers of cord in the tire casing are laid diagonally, criss-crossing one another at an angle of 30 to 40 degrees. Often the original type of tires found on muscle cars.
Body-On-Frame Construction: A type of automobile construction in which the body structure is attached to a separate frame. Common on cars until the 1970’s when car companies switched to uni-body construction on most cars (but not on trucks and some SUVs).
Boost: The amount of extra air (compressed air) pumped into the intake manifold by a supercharger or turbocharger. Usually measured in psi (pounds per square inch), inches of mercury, or bar.
Bore: The diameter of an engine cylinder or bearing. Used in determining engine displacement.
Brake Fade: A condition brought about by repeated brake applications, resulting in build-up of heat that causes a temporary reduction or fading of braking effectiveness.
Brake Horsepower (bhp): The actual horsepower of an engine, measured by a brake attached to the driving shaft and recorded by a dynamometer.
Brake Linings: The replaceable friction material which contacts the brake drum in a drum brake system to slow or stop the car.
Brake Master Cylinder: A cylinder containing a movable piston activated by pressure on the brake pedal. The piston produces hydraulic pressure that pushes fluid through the lines and wheel cylinders. This forces the brake lining or pad against the drum or disc to slow or stop the car.
Brake Pads: In a disc system, they are the replaceable flat segments consisting of a rigid backing plate plus frictional lining that takes the place of the shoe and lining in a drum brake. Brake pads are sometimes referred to as brake pucks.
Brake Shoe: The arc-shaped carrier to which the brake linings are mounted in a drum brake. They also force the lining against the rotating drum during braking.
Brakes, Disc: A type of braking system in which brake shoes, in a vise-like caliper, grip a revolving disk mounted on a wheel to slow or stop disc and wheel rotation for braking. Properly called “Caliper Disc Brakes,” they are used on most modern cars.
Brakes, Drum: A type of braking system that utilizes a metal drum mounted on a wheel to form the outer shell of a brake. The brake shoes press against the drum to slow or stop drum and wheel rotation for braking. Common on vehicles in the ’60s and ’70s, Drum brakes are only used on some vehicles rear wheels today.
Burned Piston: When a cylinder runs lean (too much air in the air-to-fuel mixture) and excessive heat burns or melts the piston.
C-Pillar: The roof support between a vehicle’s rearmost side window and its rear window. Also known as a C-Post. On a vehicle with four side pillars, the rearmost roof support may be called a D-pillar.
CAFE: The acronym for Corporate Average Fuel Economy. This single mileage figure is determined by taking a sales weighted average of the fuel consumption for all models produced by a manufacturer. The minimum required figure is an established U. S. government standard. Manufacturers which do not meet the minimum standard are fined.
Caliper: In a disk brake, a housing for cylinder, pistons and brake shoes, connected to the hydraulic system. The caliper holds the brake shoes so they straddle the brake disc.
Camber: The angle along the vertical axis of the tire/wheel when looking at the car directly from the front or the rear. Positive camber results when the top of the tire tilts out further than its bottom. Negative camber is vice-versa, and a little bit of negative camber may actually improve handling. The adjustment of this setting affects both tire wear and vehicle handling.
Cam Gear / Adjustable Cam Gear: The cam gear is connected to the end of the camshaft. The timing belt connects the cam gear to the crank. An adjustable cam gear allows you to adjust the cam without removing the timing belt.
Cam Profile: The shape of each lobe on a camshaft.
Camshaft: The shaft in the engine which is driven by gears, belts or chain from the crankshaft. The camshaft has a series of cams that opens and closes intake and exhaust valves as it turns.
Caster Angle: The forward or backward tilt of the steering axis as viewed from the side. If the point of load is ahead of the point of contact, the caster angle is positive. The caster angle tends to keep wheels in a straight line. Proper caster adjustment improves both tire wear and fuel economy.
Catalytic Converter: Often simply called a “catalyst”, this is a stainless steel canister that is part of a vehicle’s exhaust system and contains a thin layer of catalytic material spread over a large area of inert supports. It induces chemical reactions that convert an engine’s exhaust emissions into less harmful products prior to entering the environment. Made required for all vehicles sold in the U.S. starting in 1978. A car equiped with a catalytic converter cannot use leaded fuel, as it will damage the Catalytic converter.
Center of Gravity: Point where the weight of a vehicle appears to be concentrated and if suspended at that point would balance front and rear.
Closed Crankcase Ventilation (CCV): A system in which crankcase vapors are discharged into the engine intake system (usually via the intake manifold) where they are burned during the combustion process rather than being discharged into the atmosphere.
Clutch Can: The bell-shaped housing, or bellhousing, used to encase the clutch and flywheel.
Clutch Dust: Carbon dust created when the surface of the clutch discs wear as they slide together during the clutch-lockup process.
Clutch Lock-Up: The progression of clutch-disc engagement controlled by an air-timer management system.
Coefficient of Drag (cd) or Drag Coefficient: A measure of the aerodynamic sleekness of an object. The lower the number, the greater the aerodynamic efficiency. The higher the drag coefficient, the more a car’s engine must work to keep a given road speed.
Cold Cranking Amps (CCA): A rating, measured in amperes. Used for comparing cranking strength of automotive batteries during extremely cold (0 F or lower) weather. The higher the CCA, the better.
Combustion Chamber: The volume of space at the top of the cylinder where burning of the air/fuel mixture begins.
Composite Headlamps: Usually manufactured with replaceable halogen bulbs and separate hard acrylic or glass lenses. This type of lamp provides superior illumination compared to the long-conventional sealed beam unit.
Compression Ratio: The volume of the combustion chamber and cylinder when the piston is at the bottom of its stroke, divided by the volume of the combustion chamber and cylinder when the piston is at the top of its stroke. Higher compression ratios tend to increase engine efficiency.
Compressor (Air Conditioning): The machinism is an air conditioner that pumps vaporized refrigerant out of the evaporator, compresses it to a relatively high pressure, and then delivers it to the condenser.
Condenser: A device for storing electrical energy. In A/C application, an air conditioning component used to remove heat from the inside of a vehicle.
Connecting Rod: The metal rod that connects a piston to the crankshaft.
Contact Patch: The area of a tire’s tread that is in contact with the ground.
Control Arm: A suspension element that has one joint at one end and two joints at the other end, typically on the chassis side. Also known as a wishbone or an A-arm.
Coolant: The mixture of water and anti-freeze that picks up heat from the engine and transfers it to the air passing through the radiator. This transfer of heat keeps the engine operating within its optimum temperature rant preventing premature engine wear.
Cooling System: The system that removes heat from the engine by the forced circulation of coolant and thereby prevents engine overheating. In a liquid-cooled engine, it includes the water jackets, water pump, radiator, and thermostat.
Crankcase: A case that encloses the crankshaft. In most engines, the oil pan and the lower portion of the cylinder block form the crankcase.
Crankshaft: A shaft with one or more cranks, or “throws,” that are coupled by connecting rods to the engine’s pistons. The combustion process creates reciprocating motion in the rods and pistons which in turn is converted to a rotating motion by the crankshaft.
Crossmember: One of several horizontal members in a vehicle frame which join the side members and add to overall strength and stability.
CV Joint: Constant Velocity Joint — a type of universal joint used in the transaxle. They ensure that the input and output shafts are rotating at the same rate.
Cylinder Block: The basic part of the engine to which other engine parts are attached. It is usually a casting and includes engine cylinders and the upper part of the crankcase.
Cylinder Head: The removable part of the engine that attaches to the cylinder block directly above the cylinders. The head is cast from aluminum or iron and houses the combustion chambers, the intake and exhaust ports, spark plugs and much or all of the valve train. It has oil and water passages for cooling and lubrication.
D-Pillar or D-Post: The vertical or sometimes diagonal roof supporting member located at the extreme rear of the roof or greenhouse structure on station wagons and some sedan models.
Detonation: Occurs when hot spots (caused by engine deposits) in the combustion chamber ignites the air and fuel mixture prematurely. Also occurs after combustion if any unburned fuel is left in the combustion chamber. Also known as engine knock. Places great stress on the engine and leads to the destruction of the engine if ignored.
Diesel Engine: A diesel engine uses heavier weight components than gas engines to handle higher compression ratios. Typically, diesel engines run with greater efficiency and higher torque than similar size gas engines. These attributes lead to better fuel economy and towing performance. Diesel engines do not have spark plugs or carburetors. Instead glow plugs are used to preheat air in the cylinders to ensure easy starts. Once the engine is started, compression heats the fuel in the cylinders for combustion.
Dieseling: A condition in which gasoline continues to fire after the ignition has been shut off. In late-model engines, dieseling, or run-on, is caused by heat and the unusually high manifold pressure that result from retarding the spark at idle. In fuel-injected cars when the engine is turned off, fuel is automatically shut off, eliminating dieseling.
Differential: The gear assembly connected to the drive shaft that permits the wheels to turn at different speeds when going around a corner, while transmitting power from the drive shaft to the wheel axles.
Differential, Locking: The same attributes of a standard differential, except that when one wheel is slipping, the most torque is supplied to the wheel with best traction. A locking differential reduces the possibility of a vehicle becoming immobile when one driving wheel loses traction.
Directional Stability: A vehicle’s ability to maintain a true course of travel despite bumps, crosswinds, uneven road surfaces.
Displacement: In an engine, the total volume of air or air-fuel mixture an engine is theoretically capable of drawing into all cylinders during one operating cycle. Generally expressed in liters or cubic inches. Engine displacement is equal to the engine bore x stroke x number of pistons.
Distributor: A component of the ignition system, usually driven by the camshaft that directs high-voltage surges to the spark plugs in the proper sequence.
Double Wishbone Suspension (“A” Arm Suspension): A system of independent suspension in which each wheel is located on a “knuckle” that is connected by ball joints to an upper A arm and a lower A arm. Usually, the lower A arms are longer. This system provides minimal changes in track and camber when the suspension is under load, as when going over bumps or in hard cornering.
Drive Shaft: The shaft that transmits power from the transmission to the differential in a rear-drive power train.
Drive Train: The power-transmitting components in a car, including clutch, gearbox (or automatic transmission), driveshaft, universal joints, differential and axle shafts.
Dropped Cylinder: When a cylinder becomes too rich (too much fuel in the air-to-fuel mixture) and prevents the spark plug(s) from firing.
Dual Overhead Camshafts (DOHC): A DOHC engine has two camshafts in each cylinder head; one camshaft actuates intake valves and the other actuates exhaust valves. The camshafts act directly on the valves, eliminating pushrods and rocker arms. This reduced reciprocating mass of the valve train enables the engine to build RPM more quickly. DOHC designs are typically high-performance, four valve per cylinder engines. (A four valve per cylinder two intake and two exhaust design helps the engine “breathe” more freely for increased performance.)
Dynometer: A device which absorbs and measures the power derived by an internal combustion engine.
Electrolyte: Any solution that conducts an electrical current, such as a mixture of sulfuric acid and distilled water found in automotive batteries.
Electronic Control Unit (ECU): The computer that receives signals from various sensors and determines how much fuel to inject into the engine under various conditions.
Electronic Fuel Injection (EFI): A system that injects fuel into the engine and includes an electronic control unit to time and meter the fuel flow. The standard in all vehicles since the late 1980’s, but was available on 1950’s Corvettes.
Electronic Ignition System: An ignition system that uses transistors and other semiconductor devices as an electronic switch to turn the primary current on and off.
EPA Fuel Economy Rating: Comparative mileage figures generated from laboratory fuel-economy tests administered by the federal Environmental Protection Agency (EPA) using simulated weight and drag to approximate real driving conditions.
Exhaust Gas Recirculation (EGR): An exhaust-emission control system in which a portion of the exhaust gas is picked up from the exhaust manifold and sent back to the intake manifold to be reburned in the engine. Mixing exhaust gases with the fresh air/fuel mixture lowers the combustion temperature and reduces the formation of oxides of nitrogen in the exhaust.
Exhaust Manifold: The network of passages that gathers the exhaust gases from the various exhaust ports and routes them toward the catalyst, the muffler and the exhaust system.
Factory Equipment: The combination of original standard equipment and production options installed at the factory that make up the equipment of a vehicle. Does not include any accessories installed by a dealer.
Fifth Wheel: Load supporting plate mounted to the frame of a vehicle. Pivot mounted, it contains provision for accepting and holding the kingpin of a trailer, providing a flexible connection between the tractor and the trailer. Center of the fifth wheel should always be located ahead of the centerline of the rear axle.
Final Drive Ratio: A fluid coupling consists of two fan-like impellers in a sealed, oil-filled housing. The input “fan” churns the oil, and the churning oil, in turn, twirls the output “fan.” Such a coupling allows some speed difference between its input and output shafts. The automatic transmission’s torque converter is based on the fluid coupling principle.
Flywheel: A large, heavy disc that is attached to the end of the crankshaft. It adds inertia to the engine which results in smoother power flow.
Forced Induction: Any method used to force more air into the combustion chamber. Nitrous, turbo, supercharger, and everything in between.
Four Wheel Drive (4WD): In a Four Wheel Drive system, a secondary transmission assembly, called a transfer case, is driven from the main transmission. The transfer case distributes power to both axles to drive all four wheels. It is the heart of the Four-Wheel Drive system. Four-Wheel Drive can be full-time, in which power is delivered to both axles at all times or part-time, where the driver selects two or four wheel drive. Four wheel drive is often combined with independent suspension systems and off-road type tires to enhance driveability on rough, off-road terrain, or on-road driveability in unfavorable driving conditions.
Four Wheel Independent Suspension: A type of suspension in which all wheels are mounted to separate suspension members with no rigid axle connecting them. Therefore a disturbance affecting one wheel has no effect on the opposite wheel. Four wheel independent suspension reduces the un-sprung weight, improves ride and handling over rough surfaces and permits room for a larger trunk.
Front Wheel Drive: A drive system where the engine and transaxle components apply the driving force to the front wheels rather than the rear wheels. Benefits of Front-Wheel drive include: Maximized passenger space, enhanced cargo area, greater fuel efficiency and better drive traction; particularly on wet or slippery surfaces, since the drive is through the front wheels, which carry a heavier load.
Fuel Injection: A fuel-delivery system that replaces conventional carburetion. Fuel injection delivers fuel under pressure directly into the combustion chamber or indirectly through the airflow chamber.
Fuel Pump: A mechanical or electrical device that draws fuel from the fuel tank and delivers it to the carburetor or injectors.
Galvanized Steel: A specially zinc-coated steel used on many major painted panels and in key unpainted areas of a vehicle to help prevent rust and corrosion.
Gas Filled Shock Absorbers: A nitrogen gas chamber is used to pressurize the shock absorber in place of the traditional air/oil combination. Gas filled shock absorbers provide more stable damping in a variety of conditions and thus improves ride and road contact.
Gear Ratio: The number of revolutions a driving (pinion) gear requires to turn a driven (ring) gear through one complete revolution. For a pair of gears, the ratio is found by dividing the number of teeth on the driven gear by the number of teeth on the driving pinion gear.
Generator: A device that converts mechanical energy into electrical energy. It can produce either AC or DC electricity. Seldom used in automotive applications, it has been replaced by the alternator.
Halogen Headlamp: A sealed-beam headlamp with a small inner bulb filled with halogen which surrounds a tungsten filament. Halogen headlamps may increase luminous intensity at the road surface by 50 to 80 percent, as compared to the long-conventional sealed-beam headlamp systems. Many halogen headlamp systems incorporate high-beam and low-beam in one element, enhancing their serviceability.
Headers: Fine-tuned exhaust system that routes exhaust from the engine. Replaces conventional exhaust manifolds.
Heads Up Display: The digital projection of pertinent instrument data onto the lower portion of the windshield on the driver’s side. The driver does not have to take his eyes off the road to read his instrument panel.
Heel and Toe: A technique used by racing drivers that involves the use of all three pedals in a manual transmission equipped automobile. During shifting, the toe of the right foot controls the brake, while the heel of the same foot depresses the gas pedal. The left foot, of course, depresses the clutch. When executed properly, the effect is a smooth and efficient transfer of power between shifts.
Hemi: A hemi engine has a hemispherically shaped cylinder-head combustion chamber, like a ball cut in half.
Horsepower (also Brake Horsepower): A unit of measure used in representing the amount of energy or power produced by a device — one horsepower is equal to the energy required (work) to move a 550 pound object one foot in one second. Also equivalent to 746 watts.
Hydraulic: When a cylinder fills with too much fuel, thus prohibiting compression by the cylinder and causing a mechanical malfunction, usually an explosive one.
Independent Suspension: A term used to refer to any type of suspension system that allows each of the two wheels of a given axle to move up and down independently of each other.
Intake Charge: The mixture of air and fuel that flows into the intake manifold.
Lean Condition: Refers to an air/fuel mixture that has more air than fuel – which may lead to detonation.
Limited Slip Differential: A specially designed differential that not only allows the left and right axles to spin independently, but also has the ability to distribute the power to each axle even if one is slipping due to the loss of traction. A Limited Slip Differential ensures that some torque is always distributed to both wheels, even when one is on a very slipper surface.
Lockup Differential: A differential that locks the two outputs (axles) together, so there is no differential action giving you maximum traction. Generally used for drag racing where no steering is needed.
Lock Up Torque Converter: A torque converter that contains a special clutch that forms a solid connection between the engine output shaft and the transmission input shaft when a certain, pre-set speed is attained. This reduces transmission friction losses and increases efficiency.
MacPherson Strut: A suspension system that consists of a combination coil spring and shock absorber in one compact unit at each wheel. With this “independent” suspension design, road shocks at one wheel are not transferred to the opposite wheel. MacPherson struts use fewer parts, meaning a reduction on weight and fewer elements that could wear out.
Main Bearings: The bearings in the engine block that supports the crankshaft.
MAP Sensor: Manifold Absolute Pressure sensor
Multi-Port Fuel Injection (MFI): Multi-Port Fuel Injection uses individual fuel injectors to spray fuel into each intake port, bypassing the intake manifold.