Tachometer
An instrument that indicates the number of revolutions per minute at which the engine is turning. Tappet A pivoting actuator than opens and closes cylinder valves.

Tank-slapper
What happens in rare cases when a motorcycle’s handlebars slap back and forth at high speed, often due to alignment or suspension issues.

Throttle
The throttle regulates the amount of air/fuel mixture that is fed to the engine.

Throttle-body
A housing containing a valve to regulate the airflow through the intake manifold. The throttle-body is usually located between the air cleaner and the intake plenum.

Throttle-body fuel injection
A form of fuel injection in which the injectors are located at the engine's throttle-body, thereby feeding fuel to more than one cylinder. Such an arrangement saves money by using fewer injectors; but because it routes both fuel and air through the intake manifold, it eliminates some of the tuning possibilities offered by port fuel injection.

THROTTLE POSITION SENSOR (TPS)
The throttle position sensor responds to the accelerator pedal movement. This sensor is a kind of potentiometer that transforms the throttle position into output voltage, and emits the voltage signal to the ECM. In addition, the sensor detects the opening and closing speed of the throttle valve and feeds the voltage signal to the ECM. The ECM receiving the signal from the throttle position sensor determines idle position of the throttle valve. This sensor controls engine operation such as fuel cut. On the other hand, the "Wide open and closed throttle position switch", which is built into the throttle position sensor unit, is not used for engine control.

Thumper
A single-cylinder, four-stroke motorcycle engine.

Timing (ignition timing)
Timing refers to when the spark ignites the air/fuel mixture. Timing needs to be set exactly right for an engine to run correctly.

Torque
A unit of measure describing the twisting force, or leverage, an engine can exert on the rear wheel. Typically, an engine with a lot of torque will have the potential to speed up faster at lower rpms. (See also: horsepower)

TORQUE CONVERTER
A fluid coupling used in automatic transmissions to transmit power from the engine to the wheels. The torque converter allows the transmission to be engaged while the vehicle is stopped. The transmission fluid absorbs power and prevents engine stalling. This torque increase, however, is achieved at the expense of rpm and efficiency.

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. Most transmissions have 3-6 ratios or "speeds". The engine (via the crankshaft) spins too fast to drive the wheels. The transmission "reduces" the RPM and allows the engine to drive the wheels. Manual transmissions or "stick shifts" use gears as described above. Automatic transmissions usually employ turbines and a fluid to transmit power to the wheels. The rotational motion of the fluid through the transmission transfers the power from the crankshaft to the wheels. The different transmission ratios are needed to keep the engine operating efficiently. The lower ratios (ex. 1st and 2nd gears) provide the maximum torque (or twisting force) to move the car from a standstill. The higher ratios (ex. 4th and 5th gears) allow lower engine RPM for highway speeds. Generally speaking, the fewer ratios a transmission has, the less efficiently the engine operates.

Tuned intake and exhaust systems
Intake and exhaust systems that, by harnessing the pressure pulses and resonances inside the various passages and chambers of the intake and exhaust manifolds, increase the flow of intake charge into and out of the combustion chambers.

Turbocharger
A supercharging device driven by exhaust gases from the engine. The turbine, driven by hot gases in the exhaust manifold spins the compressor. The compressor increases the intake air density, and combined with additional fuel, produces more power. Turbochargers always use centrifugal-flow compressors, which operate efficiently at the high rotational speeds produced by the exhaust turbine.

Turbo Lag
Within a turbocharger's operating range, lag is the delay between the instant a car's accelerator is depressed and the time the turbocharged engine develops a large fraction of the power available at that point in the engine's power curve.

Twin Cam 88
Twin Cam 88 is the name of the Harley-Davidson engine first introduced in 1999. This engine is a 1450cc V-Twin using twin cams.

Two-stroke engine
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.