DICTIONARY OF AUTOMOTIVE TERMS - "Tw"

TWC:

Acronym for three-way catalyst

Tweak:

1. To adjust a screw or component by making a very slight adjustment.
2. To bend a component to such an extent that it will need to be replaced.

Tween deck:

The space between any two adjacent decks

Twelve:

See v-twelve

Twelve-cylinder engine:

An engine with twelve cylinders, e.g., a V-12

Twelve-valve engine:

A three-cylinder engine with four valves per cylinder (e.g., Daihatsu), or a six-cylinder engine with two valves per cylinder, or a four-cylinder engine with three valves per cylinder, i.e., two inlet valves and one exhaust valve

Twenty Foot Equivalent Unit:

(TEU) A standard for measuring container capacity on ships, railcars, etc. See containers

TWI:

Acronym for tread wear indicators

Twilight sentinel:

A device found on Cadillac cars which controls the headlights so that they remain on for a set period of time after the engine is shut off.

Twin:

To construct a highway in which there are two lanes on each side of the road often with a center median dividing each pair of lanes. The British term is "dual."
Also See:
flat twin
offset twin
parallel twin

Twin A-arm suspension:

See double wishbone suspension

Twin axle:

See tandem axle

Twin barrel carburetor:

A carburetor with two identical barrels to feed two banks of cylinders

Twincam:

An engine with double overhead camshafts.
Also See:
overhead cam
DOHC.

Twin cam engine:

An engine with double overhead camshafts.

Twin camshaft:

An engine with double overhead camshafts.

Twin camshaft engine:

An engine with double overhead camshafts.

Twin carburetors:

(TC) two carburetors on an engine, mechanically coupled and balanced

Twin-choke carburetor:

A carburetor with two identical barrels to feed two banks of cylinders. See double-barrel carburetor

Twin diaphragm pump:

A diaphragm pump with two diaphragms; if one fails the other takes over its function

Twin exhaust system:

An exhaust system with two tailpipes; either a complete exhaust system, as on performance cars and cars with V-engines, or simply two tailpipes emanating from the rear muffler. Also called dual exhaust system

Twin fitment:

See dual mounting.

Twin front pipe:

See Y-pipe

Twin header:

See Y-pipe

Twin headlight:

A headlight arrangement containing two headlights; the outer lights provide the low beams, the inner lights are for high beam

Twin headpipe:

See Y-pipe

Twin ignition system:

A distributor with two sets of contact points, each of which operates with its own coil in a separate primary circuit; the contact points open alternately, each set firing half of the cylinders

Twin I-beam suspension:

Used on most Ford trucks in the last 20 years. This variation does not link the wheels, but uses two long beams, each pivoting on the opposite side of the vehicle. Results in a smoother ride, but creates tire-wear problems.

Twin ignition:

See single-coil twin ignition

Twin overhead camshaft:

See double overhead cam

Twin-piston engine:

An obsolete two-stroke engine design featuring two cylinder barrels plus two pistons per cylinder; the pistons are linked to the crankshaft via a forked con rod or a master/slave con rod assembly

Twin planets:

Two planet gears in mesh; one meshes with the sun gear and the other with the internal gear

Twin-plate clutch:

A clutch with two driven plates separated by an intermediate drive plate; gives higher torque capacity

Twin plug ignition:

See twin ignition system

Twin port:

A cylinder head design in which there are two exhaust ports

Twins:

1. A motorcycle with two cylinders
2. Combination of a tractor and two semitrailers connected in tandem by a converter dolly. Also called "Doubles" or "Twin Trailers"

Twin-spar frame:

A motorcycle frame in which the steering head and the swingarm pivot are connected by two metal (usually alloy) members that wrap around the engine

Twin spark ignition:

See twin ignition system

Twin swirl combustion chamber:

A special design of a four-stroke engine, in which the intake valves are arranged in such a way as to ensure that the gas flow ends in two separate swirls; this design improves swirl and thus enhances combustion of the fuel/air mixture within the cylinder

Twin Trailers:

Combination of a tractor and two semitrailers connected in tandem by a converter dolly. Also called "Twins" or "Doubles"

Twin-tube damper:

See double-tube shock absorber

Twin wheel:

1. A double-rimmed wheel with two independently inflated tires; has good aquaplaning and run-flat properties.
2. Two wheels fitted to one hub

Twist-beam rear axle:

See semi-independent suspension

Twist drill:

A metal cutting drill with spiral flutes (grooves) to permit the exit of chips while cutting.

Twisted frame:

A type of frame damage often encountered as a result of the car rolling over. The left-hand and right-hand frame members are then no longer parallel and on a level when viewed from the side; instead, they are offset as if they had been turned on a horizontal axis at right angles to the frame members

Twist shifter:

A type of shift lever that is twisted to shift the gears such as GripShift models

Twisty bits:

The twisting back roads you can find in almost any state. The two lane roads that bring a sports car to life as you master the turns, curves and switchbacks.

Two bolt main:

A term referring to the number of bolts needed to secure each cap to a crankshaft rod. Most engines come with two bolt main; but racing engines have four. See four bolt main

Two-coat system:

See base and clear system

Two-cycle engine:

See two-stroke engine

Two-door:

A vehicle with one door on each side; a body design typical of all two-seater sports cars (such as roadsters, spiders) and many subcompact cars

Two-door club coupe:

See two-door coupe

Two-door coupe:

Also called the two-door club coupe, the club coupe designation seems to come from club car, describing the lounge (or parlor car) in a railroad train. The early postwar club coupe combined a shorter-than-sedan body structure with the convenience of a full back seat, unlike the single-seat business coupe. That name has been used less frequently in the 1976-86 period, as most notchback two-door models (with trunk rather than hatch) have been referred to as just "coupes." Moreover, the distinction between two-door coupes and two-door sedans has grown fuzzy.

Two-door fastback:

By definition, a fastback is any automobile with a long, moderately curving, downward slope to the rear of the roof. This body style relates to an interest in streamlining and aerodynamics and has gone in and out of fashion at various times. Some (Mustangs for one) have grown quite popular. Others have tended to turn customers off. Certain fastbacks are, technically, two-door sedans or pillared coupes. Four-door fastbacks have also been produced. Many of these (such as Buick's late 1970s four-door Century sedan) lacked sales appeal. Fastbacks may or may not have a rear-opening hatch.

Two-door hatchback coupe:

Originally a small opening in the deck of a sailing ship, the term "hatch" was later applied to airplane doors and to passenger cars with rear liftgates. Various models appeared in the early 1950s, but weather-tightness was a problem. The concept emerged again in the early 1970s, when fuel economy factors began to signal the trend toward compact cars. Technology had remedied the sealing difficulties. By the 1980s, most manufacturers produced one or more hatchback models, though the question of whether to call them "two-door" or "three-door" never was resolved. Their main common feature was the lack of a separate trunk. "Liftback" coupes may have had a different rear-end shape, but the two terms often described essentially the same vehicle.

Two-door hardtop:

The term hardtop, as used for postwar cars up to the mid-1970s, describes an automobile styled to resemble a convertible, but with a rigid metal (or fiberglass) top. In a production sense, this body style evolved after World War II, first called "hardtop convertible." Other generic names have included sports coupe, hardtop coupe, or pillarless coupe. In the face of proposed rollover standards, nearly all automakers turned away from the pillarless design to a pillared version by 1976-77.

Two-door sedan:

The term sedan originally described a conveyance seen only in movies today: a wheelless vehicle for one person, borne on poles by two men, one ahead and one behind. Automakers pirated the word and applied it to cars with a permanent top, seating four to seven (including driver) in a single compartment. The two-door sedan of recent times has sometimes been called a pillared coupe, or plain coupe, depending on the manufacturer's whim. On the other hand, some cars commonly referred to as coupes carry the sedan designation on factory documents.

Two-door station wagon:

Originally defined as a car with an enclosed wooden body of paneled design (with several rows of folding or removable seats behind the driver), the station wagon became a different and much more popular type of vehicle in the postwar years. A recent dictionary states that such models have a larger interior than sedans of the line and seats that can be readily lifted out, or folded down, to facilitate light trucking. In addition, there's usually a tailgate, but no separate luggage compartment. The two-door wagon often has sliding or flip-out rear side windows.

Two-pack filler:

All polyester fillers in use today comprise a basic filler paste and a hardener or catalyst

Two-pack paint:

Paint prepared by mixing two constituents, such as pigment and an acrylic resin

Two-piece alloy wheel:

A wheel which consists of the rim and the wheel disc or spider bolted together. The word "forged" is optional, since multi-piece alloy wheels are always forged and not cast

Two-piece forged alloy wheel:

A wheel which consists of the rim and the wheel disc or spider bolted together. The word "forged" is optional, since multi-piece alloy wheels are always forged and not cast

2+2:

See two plus two.

Two plus two:

See two-plus-two.

Two-plus-two:

(2+2) A two-door car with seating for the driver and a front passenger and only two people in the rear. It differs from a regular two-seater in that generally three people could sit in the rear seat and possibly three in the front. Usually the rear seats are very small and suitable only for children, small pets, or extra luggage.

Two-pole motor:

3600 rpm, 60 Hz electric motor (synchronous speed).

Two second rule:

The minimum gap or distance between two vehicles travelling in the same direction. As the vehicle in front of you passes a particular mark on the road or sign along the road, count two seconds and your vehicle should pass the same mark or sign. If road conditions are poor, the gap should be extended to three seconds or more. If you are following less than two seconds, there is not sufficient time to react to emergency evasive manoeuvres to avoid the possibility of hitting the vehicle in front.

Two-speed:

An electric motor or transmission having two speed settings (e.g., fan, windshield wiper)

Two-speed axle:

Axle having two selective gear ratios.

Two-speed gearbox:

See dual-range gearbox

Two-speed transmission:

An automatic transmission with just two speeds (Drive and Low) such as the GM Powerglide popular in the 1960s

Two-stage carburetor:

A compound carburetor

Two-stage pump:

A centrifugal pump with two impellers and diffusers arranged in series

Two-staged turbo:

Since there is often a lag while a turbine comes up to speed, some performance cars use two (or more) turbo units, large and small, driven by different legs of the exhaust. The smaller turbos speed up quickly giving rapid response, and the larger units provide the volume needed for high power at higher rpm's. Also see turbocharger.

Two stroke cycle:

See two-stroke cycle engine.

Two stroke cycle engine:

See two-stroke cycle engine.

Two-stroke cycle:

The operating principle of an internal combustion engine characterized by the fact that the intake, compression, combustion, and exhaust phases overlap and require only two cycles; used mainly by some motorcycle engines. On cars, the two-stroke engine was never very popular and was never produced in the USA (although Ford is experimenting with the engine); a new two-stroke engine concept with separate lubrication system and a valve system similar to four-stroke engines may combine the benefits of both the 2-stroke and the 4-stroke systems. Two-stroke engines have the advantage of rapid low-end torque (because it gets its power stroke twice as often) while 4-strokes are better at sustained high-speed.

Two-stroke cycle engine:

An engine requiring one complete revolution of the crankshaft to fire each piston once. See two stroke.

Two stroke:

A reciprocating engine cycle in which the piston takes over some of the valve functions in order to obtain a power stroke each revolution of the crankshaft. This involves the use of ports in the cylinders which are covered and uncovered by the movements of the piston. As the piston moves down, it clears these ports so that the exhaust gases can exit and a fresh charge of mixture can enter at the same time. In a typical two-stroke engine the fuel-air mixture enters the crankcase through a reed valve. When the piston is at the bottom of the cylinder a port is uncovered. As prior movement of the piston has compressed the mixture in the crankcase it flows into the cylinder. Further compression in the cylinder starts as soon as the piston reverses and covers the ports. At the same time compression is occurring in the cylinder, movement of the piston has created a vacuum in the crankcase which draws a fresh charge of mixture from the carburetor into the crankcase. The compressed charge is fired as the piston reaches top dead center. As expansion of the burning charge forces the piston downward, the reed valve in the crankcase closes and the mixture in the crankcase is compressed. As the piston uncovers the ports at the bottom of the stroke, compressed mixture from the crankcase enters the cylinder again and is deflected by a baffle on the piston head into the outer end of the cylinder. This incoming fresh mixture then assists in pushing the burned gases out of the cylinder and the cycle is repeated.

Two-stroke:

See two stroke.

Two-temperature valve:

Pressure-opened valve used in suction line on multiple refrigerator installations which maintains evaporators in system at different temperatures.

Two-tone horn:

Two horns whose diaphragms cause a column of air to resonate at two different frequencies

Two-tone paint:

A paint scheme where two different colors or two shades of the same color are used on a vehicle.

Two up:

A term for carrying a passenger on your motorcycle.

Two-valve engine:

An engine with two valves per cylinder

Two-valve head:

A cylinder head with two valves per cylinder

Two-way:

See mobile two-way radio

Two-way catalyst:

See oxidizing catalyst

Two-way catalytic converter:

See oxidizing converter

Two-way hammer:

A hammer used for dual purposes

Two-way radio:

See mobile two-way radio

Two-way system:

A turbocharging system in which, as long as the charging pressure is insufficient, the air is drawn in from a prechamber via a diaphragm valve; with rising charging pressure, the valve closes and the turbocharger delivers air via the surge tank connected to a pressure regulator

Two-way type check valve:

A unit which permits actuation of a brake system by either of the two brake application valves
Also See:
check valve
closed type check valve
open type check valve
residual pressure valve
residual brake pressure type check valve

Two-way valve:

Valve with one inlet port and one outlet port.

Two-wheel ABS:

An anti-lock brake system that operates on only the rear wheels.

Two-wheel drive:

(2WD) A vehicle's drive system in which two of the four wheels (either front or rear) are driven. Compare four-wheel drive

Two-wheel driven:

A vehicle with two-wheel drive; also written "4x2"

Two wheeler:

Trucker slang for Motorcycle as in "We got a two wheeler coming up fast in the left lane."

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