How the Chassis Dyno Relates to the Engine Dyno

Using a dyno allows the car tuner to measure the effectiveness of car modifications.

To measure a car's horsepower and torque, car tuners use a device called a dynamometer, or dyno for short. Dynos have two main types: the engine dyno and the chassis dyno. They are different in their mode of operation but perform the same basic function.

Engine Dyno Operation

For testing on an engine dyno, remove the motor from the car. Hook the engine up to one of several different types of machines that measure power created at the engine's crankshaft by causing the engine to operate an external machine. The most common of these devices is the water brake dyno, which uses a fluid coupling to perform work on a pump used in measuring engine power.

Chassis Dyno Operation

A chassis dyno measures the actual amount of power the car is putting to the ground at the wheels. You do this by putting the car on rollers, which spin in the opposite direction of the car's wheels, keeping the car in place. The rollers measure how much torque a given rpm creates in a given gear. The vehicle's horsepower is calculated from the torque measurement. The main advantage here is that the dyno run can happen while the engine is still in the car.

Power Measurement Differences

Engine and chassis dynos return different power numbers because the chassis dyno must also compensate for the power lost through the car's transmission and other drivetrain components. Engine dynos are said to measure power "at the crank," or "at the flywheel." For a chassis dyno, power is measured "at the wheels." The wheel horsepower figure will always be lower, though the exact percentage varies car to car, and dyno to dyno.

References

• Circle Track: Dyno Tech - Technology Transfer, Part V
• Car Craft: Drivetrain Power Loss - The Brutal Truth
• Steve's DIY Dyno: Dynamometers