Virtual dyno - perfexpert
 

Hi
I bought and i'm testing a virtual dyno for the android platform - perfexpert-app.com
It was about 15usd and the results seem credible so far.

Does anyone have experience with it ?

I assume you do a flat road run?

Yes, that's the idea.

I am sure that the app works as accurately as the 'accelerometer' fitted to the 'phone which I don't suppose is fantastic but probably good enough.

The ad for this app suggests that they 'measure' horsepower and torque which is clearly incorrect.

Horsepower for example cannot be measured it can only be calculated from torque and speed.

Torque can be measured by torquemeters of the type used in very sophisticated dynos.

Chassis dynos tend use either a lever arm and load cell or calculate torque from the acceleration of the drum.

The problem with any of these calculating devices is that all use Bulgarian Constants to allow for losses and arrive at flywheel horsepower.

Unhappily there is no such thing as a 'Horsepower Standard' so even the best dynos can only be calibrated against torque and speed measurement which is why it is difficult to compare values gained on different makes of dyno. Lack of standardised corrections is the real issue which makes it difficult.

If you accept the basic premise that horsepower is directly related to peak acceleration then using accelerometers is a great way to compare changes and tremendous value.

I believe that the numbers derived, whilst not accurate, will be repeatable to within a very small percentage error and the entire concept is great, just don't compare horsepower figures with those obtained in other ways as they will tend not to agree.

We bought an accurate accelerometer about 5 years ago and have used if successfully for comparative testing.

My main purpose is to compare numbers before and after some mods i'm embarking on, so i guess for that it will be useful.

Bosch had something similar "Light em up" for iPhone but does not seem to be around anymore...

This seems more "scientific"... you have to input gear ratios, tire size, CdA, weight,...

By fiddling around with these numbers you can fudge the figures to 'improve' the HP.

If you only use the system for comparison then just select sensible numbers and accept that HP figures can be out by up to 10%.

Very few of these system, for example, compensate for wheel slip which at maximum grip is around 3%.

It is interesting to use accelerometers to compare HP on hot days and cold days.