Automotive dynamometers measure a car’s horsepower and torque, with two main types: engine dynamometers and chassis dynamometers. Chassis dynos are more accurate for real-world power, but may not work for four-wheel drive vehicles. Testing a car on a chassis dyno involves strapping it down, attaching an electronic pickup, and performing three runs to determine average power. Tuners often focus on maximum numbers achieved rather than the average.
Dynamometers, in general, are a category of test devices that measure the power or torque produced by a machine. An automotive dynamometer, more popularly known as a dynamometer, is a specialized machine that calculates how much horsepower and torque a car can generate. The automotive dynamometer is popular with car tuners and mechanics, both as a diagnostic tool and a way to measure the results of performance modifications.
There are two main types of dynos, and the difference between them is whether they test power at the engine or at the wheels. The power applied to the wheels will always be less due to a phenomenon called transmission loss. A dyno that measures power in the engine is known as an engine dynamometer. One that measures power to the wheels is known as a chassis dynamometer. Chassis dynamometers offer a more accurate indicator of real world power, that is, the power that the wheels transmit at speed.
Although not always, engine dynamometers are often simply one element of a larger diagnostic system known as an engine dyno. Used primarily by car and engine manufacturers, these systems also house test devices for things like emissions, fuel efficiency, and general stress capabilities. They are often used to determine the final specification numbers that are issued through official channels when a new car is introduced. A dyno engine works through electronic sensors placed throughout the engine itself, which detect and translate the output into common units of measurement, such as horsepower.
By contrast, the basic setup of a chassis automotive dynamometer consists of a ramp and platform on which a car sits, with rollers under the drive wheels that allow them to turn without the car going anywhere. Most dynamometers only have one pair of these rollers, which means that four or all wheel drive vehicles will not test correctly. For these cars, a special four-wheel dynamometer should be used.
The rollers on a chassis dyno can either exert a resistive force against the wheels to measure power, or instead be built to approximate the forces a vehicle is subjected to when accelerating on a flat surface. These subdesigns are known as brake dynamometers and inertia dynamometers, respectively. However, the process of testing a car with an automotive chassis dyno from any of the stripes is relatively straightforward.
Once placed on the test bench, the car is strapped down and receives a general inspection for obvious defects or faults. An electronic pickup is attached to a spark plug wire to measure engine revolutions per minute (RPM). If it is a two-wheel drive vehicle, chocks are placed in front of the non-drive wheels to ensure they do not move. The car is then started and raised to about 10 miles per hour (22 kph) on the speedometer, to align the rollers. The engine is then brought up to test speed, usually somewhere around third or fourth gear.
The moment of truth comes when the throttle is pressed down to the floor, a position known as wide open throttle (WOT), until the tachometer touches its red line, at which point the pedal is lifted and the wheels slow down. speed naturally. Typically, a test involves three of these runs, with the final power numbers comprising the average of each run. However, a variety of factors can affect the total power in a given series of runs, and tuners invariably highlight the maximum numbers achieved, rather than the average.
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