Just wondering is it possible to calculate a car's wheel horsepower without running on dynos? Say if you are reading tru the ECU? I believe by recording the rpm together with the speed the same time you can find out the power band? But do the ECU log speed or just the speedometer, for non electronic speedo?

So if you reading tru the ECU you won't get the data required to calculate or plot the graph?

Where do you connect this to, the ECU? Is it standard for most cars? What kind of data does it log other than RPM?

The weight of the car can be calculated by measuring the tyre ground area & tyre pressure.

Different countries have different accessories. In Europe Aircon is optional so it would be lighter than Malaysia version.

If you have your engine rpm & speed logged, together with car + driver weight, & aerodynamic drag you can calculate relatively accurate data, not sure how often the dynos are calibrated.

Just a sidenote for dynos where do they plug in the engine to read the rpm?

How do you log the rpm and time it properly with velocity?

I don't think any reader that only monitors acceleration will be accurate as there's no other input to the data.

Important parameter other than acceleration should be time synched rpm. With this 2 data you should be able to tune the engine properly, even if the weight data is not available, just you won't get the real horsepower but good enough for tuning.