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Throttle response or vehicle responsiveness is a measure of how quickly a vehicle's prime mover, such as an internal combustion engine, can increase its power output in response to a driver's request for acceleration. Throttles are not used in diesel engines, but the term throttle can be used to refer to any input that modulates the power output of a vehicle's prime mover. Throttle response is often confused with increased power but is more accurately described as time rate of change of power levels.
Formerly, gasoline/petrol engines exhibited better throttle response in general than diesel engines. This results from higher specific power output and higher maximum engine power, as well as the fact that lower-powered diesel engines were disproportionately heavier. Recently some modern diesel engines can outperform similar sized petrol engines. Most naturally aspirated gasoline engines have better responsiveness than supercharged or turbocharged engines for engines with similar peak power outputs. However, a petrol engine may suffer from lackluster throttle response due to bad maintenance, fouled spark plugs, bad injectors, etc. Diesel engines are less likely to develop delays in throttle response, since their power comes from self-igniting fuel; plus older diesel engines have the accelerator pedal directly connected to the injection pump resulting in an instant response. This system often makes driving an older diesel engine car with manual transmission more enjoyable than with a similar petrol engine.
Several tuning factors can have an effect on the responsiveness of an engine. Throttle response in manual cars can be enhanced by dropping to a lower gear before accelerating. This action is often used in smaller cars to aid in overtaking.
Most new cars are equipped with a drive-by-wire system. Throttle response can be negatively affected as drivers feel a noticeable delay when accelerating. This delay may be caused by faulty components, by design (lazy engine developers, decreasing emissions by not allowing an old engine design to do anything harsh), or by emission controls affecting the process. Before car emissions became a general health concern, carburetors had an "accelerating pump" which made the fuel mix richer when the accelerator pedal was depressed suddenly. The resulting hydrocarbon emissions from exhausts are a main reason that emission controls became mandatory, and most petrol-engined cars operate on average in stoichiometric mix mode. Some engine manufacturers are resigned to the fact and offer lackluster performance engines. R&D costs of engines that conform to emission legislation, while still offering desirable throttle response, is one of the many reasons why the number of engine manufacturers for personal cars has drastically shrunk in the past 30 years.
Application of throttle response
Throttle response comes into play in the following situations:
Overtaking/passing requires an increase in speed, which often needs to occur quickly. This is why throttle response plays a crucial role in racing. On a spark-ignition engine, a faulty sensor or ignition may significantly delay throttle response even if the engine power curve stays the same.
- Coming out of a corner
While entering a corner, the requested power output is reduced since the vehicle is coasting or braking. After exiting the corner, a driver will often accelerate back to a previous speed. Fast throttle response allows a vehicle to regain its speed quickly after cornering. Drifting requires very precise and instant throttle response.
- Driving pleasure
Throttle response plays a major role in driving pleasure, as it gives the driver more control over the vehicle's acceleration and deceleration.
Notes and references
- "DIY: Free and Easy 2005+ Mustang Throttle Response Modification". autobglo.com (Auto B Glo). 2007-11-14. Retrieved 2008-01-19.
- Bohacz, Ray. "Eliminate Engine Detonation Without Losing Power and Throttle Response". highperformancepontiac.com. Retrieved 2008-01-19.
- Kowatari, T.; Aono, T. "Throttle-control algorithm for improving engine response based on air-intake model and throttle-response model". IEEE Xplore (IEEE). Retrieved 2008-01-19.