How does a dyno work?

[LS1 TA]

I understand you put you drive wheels on a roller that is spun by your tires as your car accelerates. My question is why are some cars dynode in different gears. Also my lillte Vector FX2 toy is telling me my car has 343 peak RWHP @ 78mph and sometimes it gives me a higher number like 358 @ 53Mph. Which number would be closet to the mph on a dyno?

[Performin Norman]

Ultimately, you want to dyno in the gear that gives a 1:1 ratio to the drive axle. In 6M GM cars, that is 4th gear. Sorry, but I can't answer the other questions.

[LS1 TA]

Ultimately, you want to dyno in the gear that gives a 1:1 ratio to the drive axle. In 6M GM cars, that is 4th gear. Sorry, but I can't answer the other questions.

Cool, thanks! that was my biggest question. So i guess my RWHP reading of the FX2 would be inaccurate becuase the gear I am in when it takes the reading isn't a 1:1 ratio.

[ConElite]

From what I know, just like Norm Said, you run it when ur drivetrain is at 1:1. Then what it does it calulates something like the Number of revolutions the drum does to the time it takes to cover that "distance." So as you punch it, the drum picks up speed and the computer calculates that distance traveled in a certain amount of time, BUt I can be comepletely wrong. Yeah 350hp at the wheels sounds kinda high but i dont know.

[benhart21]

"A dynamometer, or "dyno" for short, is a machine used to measure torque and rotational speed (rpm) from which power produced by an engine, motor or other rotating prime mover can be calculated.

A dynamometer can also be used to determine the torque and power required to operate a driven machine such as a pump. In that case, a motoring or driving dynamometer is used. A dynamometer that is designed to be driven is called an absorption dynamometer. A dynamometer that can either drive or absorb is called a universal dynamometer.

In the medical realm, hand dynamometers are used for routine screening of grip strength and initial and ongoing evaluation of patients with hand trauma and dysfunction.



Water brake dynamometer

The water brake dynamometers are very popular, due to their high power capability, controllability, and relatively low cost compared to other types. The schematic shows the most common type of water brake, the variable level type. Water is added until the engine is held at a steady rpm against the load. Water is then kept at that level and replaced by constant draining and refilling, which is needed to carry away the heat created by absorbing the horsepower (which in itself is a measure of power output of the engine). The housing attempts to rotate in response to the torque produced but is restrained by the scale or torque metering cell which measures the torque.

Electric motor/generator dynamometer

Electric motor/generator dynamometers are a specialized type of adjustable-speed drives. The absorption/driver unit can be either an alternating current (AC) motor or a direct current (DC) motor. Either an AC motor or a DC motor can operate as a generator which is driven by the unit under test or a motor which drives the unit under test. When equipped with appropriate control units, electric motor/generator dynamometers can be configured as universal dynamometers. The control unit for an AC motor is a variable-frequency drive and the control unit for a DC motor is a DC drive. In both cases, regenerative control units can transfer power from the unit under test to the electric utility. Where permitted, the operator of the dynamometer can receive payment (or credit) from the utility for the returned power.

In engine testing, universal dynamometers can not only absorb the power of the engine but also, drive the engine for measuring friction, pumping losses and other factors.

Electric motor/generator dynamometers are generally more costly and complex than other types of dynamometers."

When I was rebuilding engines and transmissions in the Marines we used water brake dynos to test everything we rebuilt.