Naturally Aspirated: Refers to an engine that does not use any form of forced induction to achieve more performance.
Neutral Steering: A condition in which the slip angle of the front and rear wheels are the same.
Nitrous Oxide (NO2): Nitrous oxide is a compound that is made up of two parts oxygen to one part nitrogen. A gas at room temperature and a liquid under pressure. When heated, it breaks down into its two elements. Often used in racing as a source of compressed air that can be forced into the motor for short periods of greater power.
NOS: Brand name/logo for Nitrous Oxide Systems
Octane Rating: A unit of measurement on a scale intended to indicate the tendency of a fuel to detonate or knock based on the percentage of isooctane in the fuel. The higher the rating, the higher the percentage of isooctane and therefore the greater the resistance to detonation offered by the fuel.
Overdrive: A gear set in which the output shaft rotates faster than the input shaft, i.e. the highest gear ratio is less than a one-to-one ratio. The overdrive feature saves fuel and, because the engine runs slower, engine wear and noise are reduced.
Overhead Cam: The type of valve train arrangement in which the engine’s camshaft is mounted above the cylinder head(s). When the camshaft is placed close to the valves, the valve train components can be stiffer and lighter, allowing the valves to open and close more rapidly and the engine to run at a higher RPM. In a single overhead cam (SOHC) layout, one camshaft actuates all of the valves in a cylinder head. In a dual overhead camshaft (DOHC) layout, one camshaft actuates the intake valves, and one camshaft operates the exhaust valves.
Overhead Valve Engine (OHV): An engine with both intake and exhaust valves placed directly over the piston. In this design, the camshaft is located in the block, and the valves are actuated by pushrods and rocker arms.
Oversteer: Where the slip angle of the rear wheels are greater than that of the front wheels. The rear tires lose grip before front tires do. Happens more often in rear wheel drive cars.
Parasitic Drag: Anything that robs power from the engine via pulleys (air conditioners, alternators, power steering, water pump, etc.) and direct connection.
Pearl Paint: A type of paint that is similar to metallic paint, but instead of minute metal particles, it uses mica. Mica is a kind of semi transparent, crystalline mineral that absorbs and reflects light in prismatic fashion. This gives a dramatic, multi-dimensional effect to the paint. Sometimes called “pearl coat.”
Pinion: A gear with a small number of teeth designed to mesh with a larger geared wheel or a rack. Used in rack and pinion steering and the differential ring and pinion.
Pitch: The up and down movement along an imaginary axis between the front and rear of a vehicle. Often during hard braking, the vehicle’s nose will “dive” or pitch down in front. During acceleration the back end will “squat” or pitch down in the rear.
Piston: A partly hollow cylindrical part closed at one end, fitted to each of the engine’s cylinders and attached to the crankshaft by a connecting rod. Each piston moves up and down in its cylinder, transmitting power created by the exploding fuel to the crankshaft via a connecting rod.
Planetary Gears: A gear set, generally found in automatic transmissions, in which all of the gears are in one plane, grouped around each other like planets around the sun. The central gear is called the “sun gear.”
Plies: The layers of cord, fiberglass, steel or structural fabric that make up the tire carcass and reinforcing belts.
Ply Rating: A measure of the strength of tires based upon the strength of a single ply of designated construction. An eight-ply rating does not necessarily mean the tire has eight plies, but rather that the tires has the strength of eight standard plies.
Polishing: Smoothing an engine’s interior surfaces, usually the cylinder heads, to improve flow characteristics and/or to prevent hot spots.
Porting: Resizing an opening so it is matched with a mating surface.
Pound-Feet (lb-ft): A unit of measure used to measure torque, that is equivalent to a twisting force of one pound placed on a one foot long lever. Generated by the engine, torque is the “push” that sets a vehicle into motion and accelerates it. Specifications charts usually include the maximum torque the engine can develop, and the RPM at which it is generated (such as 345 lb.-ft. @ 3200 RPM).
Power: Usually measured in horsepower, power is proportional to torque and rpm.
Power Band: An rpm range where the majority of the engine’s peak power is achieved. Usually starts just below engine’s peak torque and ends just above the engine’s peak power.
Power Shifting: Refers to shifting gears without lifting the foot off the gas pedal. Shifting must be done quickly or the engine will rev too high. Don’t let the engine rev more than 500 rpm between shifts. Not for the uncoordinated!
Powertrain: A name applied to the group of components used to transmit engine power to the driving wheels. It can consist of engine, clutch, transmission, universal joints, drive shaft, differential gear, and axle shafts.
Predetonation: The undesirable “knock” or “ping” that occurs when the ignition of the air-fuel mixture occurs before the ignition spark. Also known as “pre-ignition”.
Progressive Rate Springs: A spring that is designed to be stronger as it is compressed. If it takes 50 pounds of force to compress the spring one inch, it would take more than 100 pounds of force to compress it an additional inch and so on.
PSI: Pounds per square inch — used to measure pressure. Normal atmospheric pressure at sea level is 14.7 psi.
Pushrod: A general term for any rod that transfers force in compression. In a conventional overhead valve layout, pushrods are used to transfer reciprocating motion from the cam followers to a more distant part of a valve train, typically the rocker arms. Pushrods are eliminated in overhead camshaft designs.
Quarter Panel: A sheet metal panel that covers the area from the rear-door opening to the taillight area, and from the bottom of the surface to the base of the roof, or from the headlamp area to the front-door opening, and from the bottom of the surface to the base of the hood.
Quartz Halogen Headlamps: A headlamp bulb having a quartz envelope holding the tungsten filament and filled with an inert gas containing iodine or another of the five halogen gases. The gas serves to remove the tungsten deposits from the bulb wall and redeposit them on the filament, preventing blackening of the bulb surface and reduction of light output. This kind of cycle requires very high filament operation temperatures which necessitates the use of quartz instead of glass. These lamps produce more lighting power per watt of electrical power than standard sealed beam headlamps.
Rack and Pinion Steering: A steering gear in which a pinion on the end of the steering shaft merges with a rack of gear teeth on the major cross member of the steering linkage. When the steering wheel is turned, the pinion gear turns, moving the rack to the left or right, thus steering the wheels.
Redline: The maximum recommended rpms for an engine. Refers to the upper limits of the rpm scale where engine damage will most certainly occur – indicated on the tachometer by a red sector.
Resonator: A small auxiliary muffler that assists the main muffler in reducing exhaust noise.
Rich Condition: Refers to an air/fuel mixture that has more fuel than air – which may cause loss of power.
Ring-and-Pinion Gear: Any gear set consisting of a small gear (the pinion gear) which turns a large-diameter annular gear (the ring gear). Used in rear-drive differentials (rear ends) to transfer power from the driveshaft to the axle and wheels.
Rolling Radius: Tire-rolling radius is the distance from the center of the wheel to the road. Static radium applies when the vehicle is standing still. Dynamic rolling-radius described wheels in motion. The latter is used to measure tire revolutions per mile and is usually slightly higher than static radius.
Rolling Resistance: This is motion resisting force that is present from the instant the wheels begin to turn. On normal road surfaces, rolling resistance decreases with increased tire pressure and increases with vehicle weight. Rolling resistance can also be affected by tire construction and tread design.
RPM: Revolutions per minute, or rpm, is a measure of engine speed as determined by how many full turns the crankshaft makes in a minute.
SAE: Abbreviation for Society of Automotive Engineers, A professional organization that sets standards for measuring horsepower and torque and for many automotive products such as fasteners, lenses, and lubricants.
Sealed Beam Headlamp: A one piece, hermetically sealed headlamp in which the filament is an integral part of the unit and the lens itself is the bulb. Sealed beams are relatively inexpensive and when one burns out or the lens cracks, the whole unit is replaced.
Slider Clutch: A multi-disc clutch designed to slip until a predetermined rpm is reached. Decreases shock load to the drive wheels.
Slip Angle: The difference in angles between the plane of the wheel and the rolling direction of the tire.
SOHC: Single Overhead Cam — engine designed to have one camshaft control both intake and exhaust valves.
Spoiler: An aerodynamic device, normally on the rear of the vehicle, that changes the direction of airflow in order to reduce lift or aerodynamic drag. A spoiler either reduces drag or create a downward force on the car. It is called a spoiler because it “spoils” the normal air flow over the car.
Springs, Torsion Bar: A long straight bar that is fastened to the frame at one end and to a control arm at the other. Spring action is produced by a twisting of the bar.
Steering Ratio: A predetermined ratio of the steering gears. Usually, the lower the steering ratio, the quicker the response.
Stoichiometric Condition: A condition in which you have an ideal mixture of fuel and air – between lean and rich. Correct stoichiometry is reached when you have 14.7 parts of air to 1 part fuel (gasoline). Perfect combustion.
Stroke: The distance the piston travels from bottom dead center to top dead center within the cylinder.
Strut: The main support member in a MacPherson suspension system. The strut also serves as the shock absorber.
Supercharger, Supercharged: A method of forced induction in which air is forced into the intake manifold via a turbine attached to the crank pulley. Although the term supercharger usually describes a device which does the above, it can also be used to describe any method of compressing air into the engine, including turbochargers!
Suspension System : Includes springs, shock absorbers/struts, and linkage used to suspend a vehicle’s frame, body, engine and drivetrain above the wheels.
Tachometer: An instrument for measuring the speed of the engine crankshaft in revolutions per minute (RPM).
TDC: Top Dead Center — when a piston is at the top most position during the compression stroke. TDC can also refer to the top most position of the piston in the exhaust stoke, but “true” TDC is on the compression stroke.
Throttle-Body: Throttle-Body Fuel Injection is a type of Electronic Fuel Injection which positions the injector(s) centrally in a throttle-body housing. This housing contains a valve to regulate the airflow through the intake manifold.
Timing: Timing refers to the crankshaft angles at which the valves open and close and at which time the ignition system fires the spark plugs.
Tire Ratings: Tires are rated by load capacity, size and speed capacity. For example, a P225/50VR16 printed on the side of the tire means:
P = P-Metric (Passenger Type Tire)
255 = Section Width (255mm)
50 = Aspect Ratio (tire height/section width)
V = Speed Rating
R = Type of Ply (Radial)
16 = Wheel Diameter (16 inches)
Tire and wheel dimensions are the first point of information in any discussion of size and capacities. Among the other terms used to describe tires are: tread, shoulder, carcass, sidewall, bead seal, bead seat, tire diameter, aspect ratio, speed rating and section width.
Toe In: The amount by which the front of a front wheel points inward or outward. A slight amount of toe in is usually specified to keep the front wheels running parallel on the road by offsetting other forces that tend to spread the wheels apart.
Torque: A force that produces a twisting or rotating motion.
Torque Converter Clutch: An electronically controlled lockup clutch that is automatically engaged at certain speeds to eliminate the slip between the torque converter’s input and output, thereby improving fuel efficiency and performance.
Torque, Engine: Engine torque is the amount of twisting effort exerted at the crankshaft by an engine expressed in foot-pounds of force. A foot-pound represents the force of one pound acting at the right angle to the rotating crankshaft at distance of one foot in length.
Torque Rating: A measure of the engine’s power capability, whereby the amount of twisting or rotating effort being exerted on the crankshaft is expressed in lb.-ft. of force. Torque is the force that gets the weight of the vehicle moving, making it an important consideration in trailering.
Torque Steer: A tendency for a car to steer to one side when power is applied. A condition that is particular to front wheel drive vehicles.
Torsion Bar: A long straight bar fastened to the frame at one end and to a suspension part at the other. In effect, a torsion bar is merely an uncoiled spring, and spring action is produced by twisting the bar. The main advantage of the torsion bar over the coil spring in the front suspension is the ease of adjusting the front suspension height.
TPS: Throttle Position Sensor. Measures the angle of the throttle plate and sends the information to the ECU.
Traction Control: Traction control helps provide smoother, more controlled acceleration by reducing the amount of wheel spin during reduced traction conditions. Traction control utilizes the vehicle’s anti-lock braking system and is usually activated only at low vehicle speeds.
Trailing Arm: A rear suspension element consisting of a lengthwise member that pivots from the body at its forward end and has a wheel hub rigidly attached to its trailing end.
Transaxle: A transmission and differential combined in one integrated assembly, eliminating the need for a separate connecting drive shaft. This configuration is typical in front-wheel-drive vehicles.
Tuned Intake and Exhaust Systems: Intake and exhaust systems that increase the flow of intake charge into and out of the combustion chambers by varying the length, shape, or diameter of the component.
Tuned-Port Fuel Injection (TPI): Tuned-Port Fuel Injection is almost identical to Multi-Port Fuel Injection, except that tuned runners are used to channel air to the cylinder heads. This results in increased airflow to the cylinders.
Turbo Lag: The time it takes for the turbocharger to spool up and thus start to take effect.
Turbocharger, Turbocharged: A method of forced induction in which air is forced into the intake manifold via a turbine that is powered by the exhaust from the engine.
Understeer: Where the slip angle of the front wheels are greater than that of the rear wheels. The front tires lose grip before rear tires do. The angle of the steering wheel is greater than normal – requires more steering by driver. Happens more often in cars equipped with front wheel drive. Slight understeer is actually a desired condition.
Unibody Construction: A type of body construction that doesn’t require a separate frame to provide structural strength or support for the vehicle’s mechanical components. Also called “unitized.” Common method of building today’s vehicles.
Universal Joint: A joint that transmits rotary motion between two shafts that aren’t in a straight line.
Valve: A device that can be opened or closed to allow or prevent the flow of a liquid or gas from one place to another. Most internal combustion engines use intake and exhaust valves to allow fuel/air mixture into the cylinders and to exhaust burnt gases. Some engines have four valves per cylinder, which increases total valve area for increased efficiency and performance.
Valve Float: When the valves in your engine are no longer controlled by the valve springs – will quickly lead to serious engine damage.
Valve Lifter: The cylindrical component that presses against the lobe of a camshaft and moves up and down as the cam lobe rotates, opening and closing an intake or exhaust valve. Virtually all modern valve lifters are of an hydraulic design that uses a cushion foil to promote quiet operation.
Valve Train: Refers to all the components that operate the valves (including the valves) in the engine’s cylinder head.
VTEC: Variable Valve Timing and Lift Electronic Control — A Honda proprietary system in which cam timing, valve duration and lift is varied according to the needs of the driver – fuel economy (normal driving) and power (pedal to the metal). Each cam has two profiles and rpm determines the shifting from one profile to the other.
Waste Gate: A device that limits the boost in a turbocharger via a valve. The waste gate bypasses the exhaust under certain conditions. Without a waste gate, a turbocharger will destroy an engine by over boosting the intake charge.
Wedge: An engine with a wedge combustion chamber, a combustion chamber resembling a wedge in shape. Need not have parallel intake and exhaust valve stems.
Weight Distribution: That portion of the total weight of a vehicle, including equipment and payload, that will be supported by each axle and tire. Proper distribution of total vehicle weight is critical to the performance handling of the vehicle, as well as the service life of components such as the frame, axles, springs, bearings, and tires.
Weight Transfer: Weight transfer is critical to traction. Vehicles are set up to provide a desired weight transfer to rear wheels. When the vehicle accelerates, the front wheels lift and the weight shifts to the rear wheels, which makes them less likely to spin.
Wheelbase: Distance, center to center, from front axle to rear axle. Wheelbase is important because it indicates available body length and weight distribution between front and rear axles.
Wheelie Bars: Used to prevent excessive front-wheel lift
WOT: Wide Open Throttle – Throttle is open all the way as in pedal to the metal, to let in as much air into the intake manifold as possible.