A throttle valve is a device found on an automobile engine. The flow of fuel and, thereby, the amount of power the engine makes, is directly controlled by this valve. On an engine with a carburetor, the throttle valve is also referred to as the butterfly. As the gas pedal is depressed, the throttle or butterfly valve opens, allowing more air and fuel to enter the combustion chamber and resulting in an increase of power. In a fuel injection system, this valve controls the flow of air only as the vehicle's on-board computer regulates the fuel flow.
The gasoline internal combustion engine is, in reality, an air pump. The more air allowed into the engine, the more air or power is allowed to exit the engine. Much like blowing on a campfire will cause the red coals to burst into a blaze of fire, the throttle valve allows air to ignite the fuel being introduced into the combustion chamber. By introducing more air into the engine, more gasoline can be burned, resulting in an increase in horsepower and torque.
The diesel engine does not have a throttle valve. The engine's power output is not directly affected by the amount of air allowed into the system. The diesel engine's power output is controlled by the amount of fuel that is allowed into the combustion chamber. Therefore, the throttle pedal in a diesel-powered vehicle does not open a butterfly—it regulates a fuel injection pump, which controls the rate of fuel flow into the engine.
While the vast majority of production vehicles use a single throttle valve, there are some high-performance models that utilize an independent throttle valve for every cylinder in the engine. The use of multiple throttle bodies equates to a much faster acceleration rate and, ultimately, more power production. By feeding each individual cylinder on its own, performance can be enhanced by fine tuning and tailoring each cylinder to operate at its maximum potential. This individualized cylinder tuning can make up for poor intake charge as well as variations in exhaust restrictions.
The average throttle pedal controls the butterfly by means of a solid metal linkage rod or a cable. Advances in performance vehicle design have resulted in drive-by wire technology. This system uses an electronic servo that receives a signal from a transmitter located on the throttle pedal to operate a computer-controlled remote control butterfly. In this system, there is no direct link between the driver and the engine. The vehicle's computer interprets what the driver's needs are and performs the function for him.