Without the complication of a dyno hat and exhaust gas temperature sensors, the testing an
All too often a dyno is inaccurate, not by design, but due to improper installation in the test cell, the air exchange capability, and/or the electrical and water supply, along with a host of other factors. The best made dyno can provide falsely optimistic or pessimistic data due to operator or installation error. There is much more to dyno testing than just buying the unit. This is why we felt it important to provide this primer prior to our dyno test of our 467 Mule engine.
RaceKrafters employs a Model 800 Stuska brand water brake that was modified by Depac. It’s integrated with the latest Depac control system and data acquisition. The brake has the ability to hold 2,000 hp, and uses a water supply that enjoys 90 psi of pressure with the load valve closed and about 55-60 psi during a full power pull. A general rule is 10 gallons per minute of water are required for each 100 hp absorbed. A 1,000hp dyno would require about 100 gallons of water per minute at a flow of around 60-70 psi. A 300-gallon tank holds the water for testing and is sent to the brake with a large centrifugal pump. The water is not recycled, so cooling is not a concern. When the water is reused, it then needs to be cooled to allow accurate control of the resistance created by the brake.
The engine is mounted on a stand called a dyno cart and is attached from the flywheel to the water brake with a coupling. The brake has two water lines going to it: an inlet and an outlet. In simple terms, it can be thought of as a water torque converter that causes resistance against the engine. A strain gauge is employed to measure engine torque, which is mathematically converted to horsepower. The equation is:
Horsepower = torque x rpm/5,252
Horsepower is a calculation that was derived a few hundred years back by James Watt to sell steam engines. With any engine, both horsepower and torque are equal at 5,252 rpm. This is due to the numerator and the denominator being the same and thus, becoming one. If you do not believe this, then get out your calculator and using the dyno sheet from the tuning story that follows, compute the horsepower from the torque and rpm.
A simple way to look at a dyno is the water brake loads the engine until it is pulled down to a certain rpm, and then the torque is read. This procedure can be controlled by the operator with a load (water) valve or though a control system, such as the Depac employed at RaceKrafters. There are a number of companies that make dyno control systems, Depac being one of them. Over the years, most load control manufacturers also integrated data collection, making the PC-based system very accurate and able to provide finite readings.
In contrast, in the good old days the dyno would be operated manually with a load (water) control valve and it would require at least two other people: one to watch the torque meter, while the other watched the tachometer. A pull would be made and then each would report the numbers they saw and the power would be calculated using the equation supplied in this primer.