RPM based Horsepower calculation

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RPM based Horsepower calculation

Postby Querlenker » Mon May 01, 2017 8:20 pm

Hi Harry,

I drive a classic sportscar with a modified engine and am looking for a solution to evaluate changes made to the engine.

For this, I would like a solution that generates hp and torque vs. rpm graphs.
I believe that GPS-based acceleration is not accurate enough for this, plus I wouldn't have the rpm information.
Using a complete vehicle model combined with all required parameters and an accurate rpm vs. time signal should give very accurate results.

From what I read in one of the other posts, I think you have this vehicle model.
What I haven't understood yet: do you use the method described above when a OBD dongle is connected?

Second question: is there way to get rpm info into your app on an old car without OBD?

I actual own an old device that does exactly this, called a Road Dyno (http://www.dynoplus.co.uk/roaddyno.shtml), but would much prefer a modern solution.

Thanks for your time, I love my Laptimer app and would love even more to be able to use Dyno with rpm vs. time without OBD.


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Re: RPM based Horsepower calculation

Postby Harry » Wed May 03, 2017 9:03 pm


LapTimer uses several OBD parameters plus the vehicle configuration to derive power and torque developed. This means LapTimer derives these values bottom up using a "engine simulation". Without OBD, Dyno will deliver acceleration times only. The only option to get the parameters required ist Autosport Labs RaceCapture solution. But this requires you to wire individual sensors - which is considerable effort.

It is possible to derive power from acceleration, vehicle mass etc, this mode is not supported by Dyno / LapTimer currently.


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