Dyno usage

Category: Dyno usage

CVTs normally consist of a set of two pulleys that can change their width and a belt that can travel from a closer position in the drive pulley (and a more open position in the driven pulley) which works as a first gear, to a wider position in the drive pulley as the drive pulley becomes compressed (by centrifugal rollers or other mechanisms) which work as a high gear. An important feature of CVTs is that it exists infinite positions between the “low” position to the “high” position, which gives also multiple combinations for the ratio value which change during the test, thus it is NOT possible to perform a standard ratio calibration for CVTs.

There are two ways to test a vehicle with a CVT (Continuous Variable Transmission)

Testing the CVT on its normal way of operation.

  • Set Fixed Ratio = 1.000 (as the ratio changes during the whole acceleration phase) and
  • use the starting and ending points referenced to speed. Note that it is also possible to start from a standstill either using manual start or setting the starting speed to 1 km/h
  • The resulting test should be displayed as HP (wheel) vs Speed.
  • Aux Torque can be used to get the Linear Force (thrust), but not ETQ
  • Remarks:
    • It is not possible to get the engine HP and the graphs vs actual the RPM (and makes not much sense). As the clutch is centrifugal in most cases the only way to disengage it is LIFTING the wheel and blocking the wheel, but this is a complicated and risky maneouver
    • Also, it is not possible to get the actual engine TQ, it is better to use the second method (blocked CVT)

Testing the CVT with the pulley blocked in the “high gear”

This is the method to get the most information from the Engine, almost the same as a vehicle with a manual gearbox (with the limitation of the centrifugal clutch)

  • Depending on the type of CVT, the pulley with the rollers may be set in a fixed position using washers, then the CVT will act as a fixed gear (high gear)
  • When this modification has been performed, it is necessary to start the engine carefully as the clutch will start the vehicle in the high gear. The recording at full throttle shouldn’t start until the clutch is totally engaged. For instance if the vehicle normally gets the clutch totally engaged at 15 km/h, it is possible that with this modification this happens at 30 km/h
  • When a test is recorded in this way, WHP and ETQ (uncorrected) channels are available vs actual Engine RPM, but EHP and corrected TQ are still not available due to the fact that the cetrifugal clutch is quite complex to be disengaged at top speed.

Displaying graphs vs actual Engine RPM

The X-Y graph can be used to display the graphs vs actual RPM (if the Engine RPM channel has enough quality), but in our opinion the resulting graph can be very confusing compared with the graphs-vs-speed, because indeed the purpose of the CVT is to keep the RPM almost constant during the widest (speed) range as possible

Press CTRL+F3 to enter the X-Y graph, and choose the 0x31-Engine RPM for the X axis

Category: Dyno usage

In an inertial dyno RAW power (power observed at rollers) is basically the same as the Wheel power (power that is available at wheels), with the only exception of the power lost at bearings, which can be ignored.

But in a braked dyno using air-cooled eddy current brakes, part of the power is used in the air-pump work in the brake rotors, specially for roller/brake speeds over 2000 RPM.


The power wasted by the brake in the air-pump effect could me measured doing a high speed coast down test, but this is a complicated test due to the speeds and power levels involved.

Category: Dyno usage

Inertial tests: it is common that the longer the test (higher gear) the more power that the engine can develop, this happens for two reasons: 

  1. Engine Inertia (which is unknown) causes that part of the power is used for accelerating the engine itself. For higher gears the most of the power is used to accelerate the rollers, and as the gear becomes lower the amount of power for accelerating the engine is higher. This maximum happens at first gear (in some engines it could be even about 50%), and of course at Neutral position it is 100%
  2. If it is a turbocharged engine, the time that the turbo has for reaching its top pressure is lower in lower gears than it higher gears

Braked tests: Both issues are considerably attenuated when performing braked tests of a same duration.

Additionally, In twin roller dynos there is also another source of differences, which is the tyre deformation: normally the lower the gear the higher the pressure that the tyre does against the front roller and the higher the losses, but these losses cannot be measured in the coast down phase. Then my recommendation is using the higher gear possible in these dynos, and even increase the tyre pressure to reduce the deformation (but if you see that slippage increases then you should reach a balance)

example of tyre deformation

Category: Dyno usage

In most cases we need to know an estimation of the Power at Engine, which implies to record the coast down phase: friction losses from tyre losses and air-pump losses from brake mainly. This coast down phase must be recorded with the clutch pressed or the Neutral position selected

  • Open Gauges Window
  • Configure the test:
    • Enter data: Vehicle and Customer.
    • Mode: Inertial or ramp,
    • Starting RPM and ending RPM (for instance 2000 to 6000 RPM), also test duration for ramp test (for instance 10 to 15 sec). Important the ending RPM must be slighly lower than actual value, for instance if the engine reaches 7500 we could set 7000 as top rpm, and the SW will allow us to continue up to 7500 if we want to.
    • Stopping mode: normally “Stop When Lower” mode, so the CLUTCH message is shown and the coast down phase is recorded
  • Calibrate the ratio: (check the Ratio calibration topic)
  • Press “continue” or the start/stop button to enter the semaphore window
  • Prepare the vehicle at a speed below the starting RPM
  • Open full throttle. If in ramp mode, wait until the pre-load and stabilisation ends
  • The test will start automatically
  • When ending RPM is reached, the clutch message will be displayed, but the user can continue accelerating if the engine top speed has not been reached
  • Press the clutch / Enter Neutral and wait until the recording ends
  • The test will stop automatically when speed is below the point set at configuration (by default 50% between starting speed and ending speed)
Category: Dyno usage

Important: the software only uses the Roller Channel for all calculations related to the engine (Transformation from Roller Engine scale to Torque at Engine, and Calc RPM for Graph’s Engine RPM axis). This is done in this way for two reasons:

  1. because some engines cannot always provide Engine RPM readings, for instance diesel engines or engines based on pressured air, or others, and
  2. because the engine RPM Channel is often a problematic channel, specially in multi-cylinder engines. Only when the Engine RPM channel is read from an ECU the data can be 100% reliable For this reason the software is based on the calibration of Ratio value, which is the relationship between Engine RPM / Roller RPM. For instance if the engine is running at 3000 rpm while the rollers are running at 1000 rpm then the ratio will be 3.0

How to calibrate the ratio:

There are five options:

  • Using RPM clamp, when using any of the clamps, or in general the Engine RPM TTL input (for instance from the ECU) the software will be updating the ratio value while the vehicle accelerates at the Gauges Window, or also after the first run.

How to use it:

  1. the user should engage the gear that is going to be used for the test,
  2. then accelerate progressively and the SW will be updating the ratio value while the acceleration persists,
  3. then when the ratio value is stable, the ”Update” button can be disabled to block this value, or the mode can be set to Fixed Ratio, so it does not change anymore.
  4. Then the test can be started as usual either using the start and stop RPM values (this works for inertial and ramp tests).

On the other hand, if the ratio was not calibrated before starting the test, even despite that SW can calculate the correct Ratio value after the test is done, the starting and ending RPM values shouldn’t be used because they will cause random starting and ending points. Alternatives:

    • Use either manual start/stop (only for inertial)
    • Use start and stop referenced to SPEED
  • Use OBDII, ECU or XDS data. This method works in the same way that the option 1 (clamp): the SW updates the ratio while the vehicle accelerates at the Gauges window, but the main difference is that the source of Engine RPM value is not the Engine RPM Channel (0x31) but the OBDII/CAN/ECU channel 0x91. The rest of the operation is the same. This external source can be also used at the Manual Calibration Window.
  • Fixed Ratio. This is not an actual calibration method, but a mode to keep the latest determined value fixed once it has been determined by other methods
  • Manual Ratio Calibration. When there is no way to measure the actual RPM, or the user don’t want to spend time connecting clamps, interfaces or whatever, the SW still is able to find the ratio using the vehicle’s tacho in a visual way. The procedure is simple:
    • Open the Ratio Calibration Window (button or CTRL+F7)
    • Set a RPM reference. Typically aprox of top rpm /2, for a diesel engine a typical value would be 2000 rpm, and for a petrol engine 3000-4000 rpm depending on the engine
    • Accelerate using the gear which will be used for the test until the engine reaches the previously set reference (2000, 3000, 4000…)
    • and then click on “Continue” or use the start/stop switch (when it is installed). The software will use the reference and the current roller speed to determine the ratio. For instance reference is 3000 rpm and roller is 1000 rpm, the ratio = 3.0

Note that the OBDII/CAN data can be used here too, the main difference is that the user will not need to be so accurate to set the engine to the exact speed that the reference points, because the reference will be updating in real time, thus if the engine is running at 3050 rpm instead of 3000 rpm it will not be important because the reference will be also 3050.

  • Ratio manual calculation, based on gearbox and transmission calculations