Glossary

AMG — A Mercedes-Benz subsidiary that transforms the company's standard production cars into high-powered hot rods by extensively modifying the stock engines and bodywork.

Cabriolet — A convertible with a padded, multilayer fabric top that, in effect, makes the car a soft-top coupe. Some enthusiasts call them "cabs." Different from a roadster.

Continuously variable transmission — A belt or chain running between two pulleys transfers power from the engine to the driveshaft. As the pulley driven by the engine slowly expands, the pulley driving the wheels contracts, thus continually varying the ratio between the two.

DOHC — An acronym for dual overhead camshafts, a complex but efficient mechanism to control the opening and closing of an engine's intake and exhaust valves.

Dry sump — A lubrication system found mostly on race cars and the highest-performance sports cars like the Chevrolet Z06. Virtually all passenger-car engines are "wet sump," having a limited amount of lubricating oil in a chamber, or sump, at the bottom of the engine. This makes the oil less effective at cooling the engine and creates some resistance for the crankshaft and connecting rods. Dry-sump race car engines carry a larger quantity of oil in an external tank, where it can also shed some of the engine's heat. This system also allows oil to better circulate and so lubricate the engine during high speeds or sharp turns that otherwise might hamper a wet sump system.

Electronic stability platform — A sophisticated form of traction control that automatically brakes individual wheels to help prevent a car from oversteering ("spinning out") or understeering (sliding straight off the road rather than turning with a corner).

Exotic — Any car made in small production numbers, typically costing $200,000 or more and capable of speeds close to and even in excess of 200 mph. Also, not surprisingly, called supercars.

Manumatic transmission — A fully automatic transmission, but one that gives the driver the option of selecting the speeds manually, with a lever or buttons. Sometimes called "auto-sticks," and not to be confused with sequential manual transmissions.

Power-to-weight ratio — The curb weight of a car divided by its engine's horsepower. For a typical family sedan, the power-to-weight ratio would be around 19. For a 3,400-pound, 500-hp Dodge Viper, it's 6.8, meaning that each "horse" has only 6.8 pounds of car to propel. The lower the number, the better the ratio from a performance standpoint.

Roadster — A two-seat sports car with a relatively simple fabric top or entirely removable metal or fiberglass hardtop. Not to be confused with a cabriolet.

Sequential manual transmission — Sometimes called a "sequential manual," these transmissions have no clutch pedal. The gears are shifted and the clutch operated electro-hydraulically rather than by the driver moving a shifter and depressing a clutch pedal. Buttons or spoon-shaped paddles on the steering wheel or steering-wheel column replace the shift lever.

Specific power — A figure that denotes how much horsepower per unit of displacement an engine makes. For example, the Ferrari F430’s 4.3-liter V8 engine produces 113 hp per liter for a total of 483 hp. Vehicles with specific horsepower this high are few.

Sports sedan — A four-door car with performance-tuned suspension and steering, and a high-performance engine, often equipped with a manual transmission.

Supercharger — An air pump driven by the engine, via a belt or gears. By forcing more air (and thus fuel) into the engine's combustion chambers, it increases horsepower.

Traction control — A system that automatically cuts or reduces the throttle if it senses that a drive wheel is spinning as a result of excessive power application or a slippery surface.

Turbocharger — An air pump to increase horsepower driven by an engine's hot exhaust gases spinning a turbine. The turbine drives a compressor that forces more air (and thus fuel) into the engine's combustion chambers, which increases horsepower.

Wankel engine — An engine that, instead of reciprocating individual pistons inside cylinders, has one or two triangular "rotors" spinning eccentrically inside chambers. The eccentric motion of the rotors continually creates pockets where combustion of the fuel/air mixture takes place, and the explosions keep the rotors — and thus the driveshaft — spinning. See our sidebar on the Mazda RX-8's rotary engine for more information.

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