Ever wondered what happens when your tuner puts your car on a dyno? In this article we lift the veil on the black magic of Dyno Tuning.
Types of Dynos
There are three main types of Dynamometers, an Engine Dyno, a Hub Dyno and a Chassis Dyno. Each with its own set of benefits and drawbacks.
An Engine Dyno is great for getting very consistent results in very consistent conditions. The engine is removed from the car or put straight on the engine dyno after being built and connected directly to the dyno load cell (with no gearbox).
The engine dyno’s water cooling supply, fuel system and sometimes ignition system would be connected to the engine and it would be started and ready to tune. This is often a very time consuming task and better suited for engine development programs or an engine that would be modified over several weeks or months.
If you don’t want or need to remove the engine from your car, a Chassis Dyno is a more practical option. A car’s driven straight off the street, strapped down to the rollers and is ready to be tuned.
This is certainly the fastest way to get tuning, but it does have its drawbacks. The car is strapped into the rollers using a method where the harder the car wants to pull forward the more the downwards force increases. This results in the car pulling harder down into the rollers.
This works really well and provides consistent results – up to a point, after which you end up fighting the traction limit of the tyre. This limit is normally around 800-1000hp depending on a car and/or the dyno setup.
The chassis dyno is ideal for getting cars making up to around 800hp on and off quickly with minimal setup time.
Then, we have the Hub Dyno, which is bolted directly to the vehicle’s drive hubs, eliminating the wheels and tyres altogether. This is a great solution for high powered race and street cars and a great “in the middle” solution between Chassis Dynos and Engine Dynos.
You can have accurate, repeatable results in cars that are making well north of 2000hp, or you can fine tune a 400hp street car. The downside is there is a little more setup time involved than in a Chassis Dyno and each vehicle’s stud pattern and rear end length may need a different adaptor to bolt onto the dyno.
How Dyno works
Regardless of the dyno style, it needs to perform the following functions:
• Measure the retarder speed. (from a speed sensor found on the roller shaft)
• Control the rate at which the retarder shaft spins.
• Measure the load at the retarder arm. From a load cell found mounted between the retarder and the dyno chassis. This mechanical connection is the only thing stopping the retarder from pivoting forward, and the only thing that’s measuring how hard the retarder is being forced against the dyno chassis.
In order to control the rate of acceleration of the roller, or to hold a particular roller speed there is an “Eddy Current Retarder” attached the end of the common shaft that the car is sitting in. There is typically one or two for each bed, more retarders means more muscle to hold more power! Our particular dyno has one retarder per bed.
The eddy current retarder is commonly found in roller coasters and train brakes and works by applying a specific amount of electrical energy into the unit in order to provide the required amount of resistance or braking force. The result of this effort is heat, which the retarder disperses with its own internal fan like design in order to keep the retarder core temperature to a minimum.
Because we know the roller speed and we know the force being applied to the load cell we can calculate the amount of Horsepower generated using a fancy formula which is:
So what does it all mean? On our Chassis dyno it means we can hold a car at any consistent road speed and any engine load in order to measure the power output and adjust the engine management system until the engine is making the most power at that point – this is known as “Steady State Tuning”
We can also do a ramp test allowing the engine to go from 2000RPM to 7000RPM over 15 seconds, essentially choosing how many meters or feet per second the dyno will allow the engine to accelerate at. This is known as a “Power Run”
With the Steady State Tuning done, we can then adjust the engine management parameters at all load and RPM sites in order to make the most power at each RPM and Engine load.