• Frequently Asked Questions

    If you can't find your answer here, feel free to contact us

    Do I need to connect PerfExpert to my car ?

    How PerfExpert can estimate my engine power and torque ?

    How does PerfExpert know the engine rev, as it's not connected to the car ?

    Does PerfExpert manage the influence of atmospheric condition on engine performance ?

    What result accuracy can I expect from PerfExpert ?

    Does PerfExpert can be used on a motorbike?

    My car has an automatic gearbox, can I dyno it with PerfExpert?

  • Do I need to connect PerfExpert to my car ?

    No, you don't need to connect your phone to your car to use PerfExpert.

     

    By default, PerfExpert relies on the internal sensors of your phone or tablet to measure your car acceleration. This requires that your phone is firmly mounted inside your car, and that each measurement is started from complete halt (0 Mph).

     

    There is an option allowing to connect PerfExpert to some specific external GPS. It can be enabled on Android from the Account screen (by pressing the "Upgrade to Pro" button) and on iOS from the Settings screen (by enabling the "Use VBox Sport" tooggle). With this feature, measurement procedure is simplified:

    • Dyno measurement car be performed from a rolling start
    • The phone doesn't need to be mounted in a specific position in the car
    • The Pitch parameters from the car profile is ignored, so it doesn't need to be adjusted

    This is perfect for intensive users!

     

    Currently the compatible devices are the following:

    More hardware will be supported in the future like some specific OBD2 dongles and other external GPS. External device connection is a paid option that require a time-based subscription.

  • How PerfExpert can estimate my engine power and torque?

    PerfExpert prompts you to provide some of your car characteristics in a 'car profile'. Then, from both the measured acceleration and the car profile, PerfExpert can estimate power and torque thanks to our physical model.


    This model takes into account losses between engine and the wheels (transmission, rotary inertia), and also losses due to the external environment (air resistance, rolling resistance). PerfExpert therefore performs a realistic estimation of all these losses to retrieve flywheel (crank) and wheel power from the power actually measured.
     

    To be accurate, the model needs to know the following characteristics of the measured car, at the time of measurement :

    • Total weight (app helps you to take into account fuel level and passengers weights easily)
    • Engine displacement
    • Tire sizes
    • Drag area (app provides you a way to estimate it from the drag coefficient)
    • Car speed at 1000rpm on the measurement gear
    • Car suspension stiffness

  • How does PerfExpert know the engine rev, as it's not connected to the car?

    From the information you entered in the car profile, PerfExpert know the overall ratio of your car transmission. So from the car speed, PerfExpert can compute back the engine rev.

  • Does PerfExpert manage the influence of atmospheric condition on engine performance?

    Yes, PerfExpert applies a correction ratio to power, based on the weather conditions at the time of measurement, in order to to bring back the power of your engine to the power it would produce in normalized atmospheric conditions. You can use one of five international standards currently in use by car manufacturers : DIN 70020, SAE J1349, CEE/E, JIS D 1001, and ISO 1585.

  • What result accuracy can I expect from PerfExpert?

    This accuracy not only depends on PerfExpert or the smartphone used, but also on how rigorous you are while performing the measurement procedure. It also depends on the in-car phone mounting quality when using the default internal sensors mode, and on the number of connected satellites when using the VBox Sport feature (iOS only, optional). Following perfectly the measurement procedure, results accuracy can reach 0.5% for Timed runs and 2% for dyno tests.

    You can see some examples of PerfExpert dyno results compared to chassis dynamometers here.

  • Does PerfExpert can be used on a motorbike?

    PerfExpert has been designed to be primarily used on cars. As a result, we will not provide support to help you using it on a motorcycle.

    However, if you managed to properly mount your phone on a motorbike, you will most likely be able to use the Timed Run test mode without any issue. Also the Dyno test mode could be usable too, providing realistic horsepower and torque curves shapes, but the values could be inaccurate.

  • My car has an automatic gearbox, can I dyno it with PerfExpert?

    There are two test modes in PerfExpert : Timed Run (elapsed time of car acceleration) and Dyno (power and torque). The Timed Run test mode can be used on any car, and even on a bike, while the Dyno test mode is designed to be used on an internal combustion engine powered car, equipped with a mechanical gearbox. PerfExpert Dyno needs that the ratio between the car speed and the engine speed (rpm) remains constant during the whole measurement. This means that the gearbox must allow to keep the same gear when accelerating from low engine rpm to max engine rpm.

    Dyno mode is compatible with most automatic gearboxes like the DSG (VW), Tiptronic (Audi), 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 (like most CVT gearboxes).

     

    See this article about PerfExpert dyno testing with automatic gearbox for more details.

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