There are two test modes in PerfExpert : Timed Run (elapsed time of car acceleration) and Dyno (power and torque measurement). The Timed Run test mode can be used on any car, and even on a bike, while the Dyno test mode is (for now) designed to be used on an internal combustion engine powered car, equipped with a mechanical gearbox. The reason for the mechanical gearbox is that PerfExpert Dyno needs the ratio between the car speed and the engine speed (rpm) remains constant during the entire measurement. This means the gearbox must allow to keep the same gear when accelerating from low engine rpm to max engine rpm. So a manual gearbox is perfect for dyno testing, but we know that, nowadays, more and more cars are equipped with automatic gearboxes.

Dyno mode is fully compatible with most automatic gearboxes like the DSG (VW), some Tiptronic (Audi), some Steptronic (BMW)... but is not compatible with automatic gearboxes that doesn't have a manual shift mode, or that can't maintain a constant ratio during the entire acceleration (like most CVT gearboxes).

It’s important to know that if your automatic gearbox has a torque converter, power and torque displayed by the app may be distorted when there are variations of the ratio between wheels and engine speeds (torque converter is slipping). Once it’s “locked-up”, this ratio becomes constant and PerfExpert can estimated engine power and torque as for a manual gearbox. You can easily hear when there is slipping at full acceleration (wide open throttle = WOT) at low rpm, remember to not pay attention to power and torque for this part of the measurement, the best would be to increase Minimum rev to not display this part of the measurement on the chart.

Procedure

Here are the three most important things to care about when performing dyno measurements with an automatic gearbox.

1. Make sure to put the gearbox in manual shift mode

The best thing to do is to go into your car’s owner manual to check how to put the gearbox into manual shift mode. Indeed, each car may have different ways to do so. You must select the mode that will allow you to manually engage the gear you selected in the test preparation, and that will allow you to WOT at low rpm, just about 200rpm below the Minimum rev set in the test preparation.

BMW Steptronic gearbox : in D mode, push to the left to set manual sport mode.

2. Make sure to not trigger the Kickdown during measurement

Once you have completely engaged the right gear, car rolling at the right speed to get engine rpm approx 200rpm below the “Minimum rev”, you are ready to WOT. When doing so, make sure that you don't push the "kickdown" button that is at the bottom of the pedal. You must press accelerator to it's maximum but without pushing the "kickdown" button. This is very important to prevent the gearbox to automatically shift down at the beginning of the measurement.

Check this 2003 VW Golf MK4 2.0 Automatic example :

The kickdown button is located at the end of the accelerator pedal travel.

3. Release accelerator pedal at max engine rev

When you reach the maximum rpm, release the accelerator pedal immediately. This will prevent the app from continuing the measurement on the upper gear, in case the gearbox has automatically shifted up.

Here is an example on the BMW 530d Steptronic:

530d Steptronic Dyno measurement. This video also shows the VBox Sport mode, allowing measurements from a rolling start, without the need to mount the phone inside the car.

Hope this document helps you to better use PerfExpert on your automatic car and to understand better your results.

Feel free to ask questions and leave comments!