Frequently Asked Questions
What is a dynamometer?
A dynamometer, or dyno as it's normally called, is a machine used for testing of vehicles in exacting and repeatable conditions. With a dyno you can run a motorcycle at nearly any speed and measure the computed horsepower by how hard or fast it spins the drum inside the dyno.
What is tuning?
An engine runs best with a correct ratio of air to fuel called stoichmiometric mixture. That mixture is generally between 13.2 through 14.7 parts air to 1 part fuel. When the motorcycle is running on the dyno the exhaust gas is analyzed to determine if the mixture is correct. Too much fuel and the mixture is "rich" and too much air and the mixture is "lean". A motorcycle can be lean at some RPMs and /or throttle positions and too rich in others. Changes are then made to the motorcycle's fuel injection or carburetors to correct the fuel ratio and thus obtain the most potential from the engine.
How is the motorcycle tuned?
On a carburetor, changes are made by replacing or adjusting parts of the carb. Parts like jets and needles that control the flow of fuel can be replaced or modified with a "jet kit". Fuel injected bikes can be modified with a Power Commander or by reprogramming or replacing the stock computer.
How does a Power Commander work?
Inside the computer of fuel injected motorcycles is a "fuel map". At given throttle positions, RPMs and other factors like air density and temperature the computer uses the fuel map to tell the fuel injectors how much fuel to spray into the engine. When changes are made to the motorcycle that effect the amount of air the engine uses (like an aftermarket exhaust or air filter) then changes to the fuel map need to also be made. A Power Commander intercepts the signal going from the computer to the injector and modifies it to add or subtract the right amount of fuel to make the appropriate air / fuel ratio.
What is Tuning Link and how does it work?
Tuning Link is a software program developed by Dynojet for use with their dynos to tune their Power Commanders. While the bike is being run on the dyno at different RPMs and throttle positions the air / fuel ratio is constantly being computed. Changes to the Power Commander are made automatically by the Tuning Link software while the bike is running! Before Tuning Link the motorcycle would be run through the RPM range on the dyno at a given throttle position. Then the air / fuel ratio is calculated by the dyno operator at different RPMs of the run. Those calculations are then entered by hand into the Power Commander. Another run is then done at the same throttle position and differences noted. That cycle continues until the dyno operator is satisfied with the "tune". Tuning Link is a quicker and more exacting tune!
Do I need a custom map?
There are a lot of downloadable Power Commander maps. Just as off-the-rack clothing of the same size may not fit just right, custom tailored clothing is made exactly to your size. Every bike is a bit different so not every map fits every bike. Even with a map that was made on the same bike with the same equipment there is always room for improvement.
Does dynoing hurt the motorcycle?
No more than riding it on the road does.
Why are dyno readings between dynos different?
Horsepower is a computed figure based upon how much torque an engine produces. The torque of the motor is measured on a dyno by how quickly it can rotate a drum of a given weight. Several variables like bearing wear, lubrication, temperature, etc can effect how easily or hard the drum can be rotated thus skewing the torque reading of different dynos or even the same dyno on different days. An eddy current dyno produces more repeatable and consistent results by controlling the speed of the drum that the motorcycle is turning. The DynoJet 250i also samples air pressure, temerature and humidity within the room. It uses this data to apply a "correction factor" to the computed data. Since engines generally run better in cooler air with less humidity the motorcycle run at different times could show different output readings. The correction factor ensure that the operator is comparing "apples to apples" when looking at runs from different times.
How do you read a dyno sheet?
We normally have 3 lines on our dyno sheet: horsepower, torque and air/fuel ratio.
This sheet shows three dyno runs from the same motorcycle. The motorcycle was run in 4th gear at 100% throttle position.
The taller line in the upper chart indicates horsepower (upper left vertical scale) at given RPMs (across the bottom scale). This is commonly called the "power curve".
The other line in the same graph is torque measured in foot / pounds at given RPMs.
The lower graph shows the air/fuel ratio as the motorcycle goes through the RPM range. The red dotted line indicates a target air/fuel ratio of 13.2 to 1. Below the line indicates a rich condition and above the line a lean condition.
In this graph you can see that at 100% throttle the bike is rich between 7,000 and 11,000 RPMs. Compare the power curve to the air/fuel ratio and you can actually see the relation between areas of proper air/fuel ratio and areas that can be improved through tuning. |
