Dyno testing turbo cars

[Brian Renegar]

>If I have recorded data for my car (RPM, Driveshaft, G-meter) how can I
>calculate the Torque and HP curves given this data.
>
>Does anyone know the formulas and physics involved?

Torque = (g force * weight * rolling radius) / (trans gear ratio * axle
gear ratio)

Rolling radius is the "effective" radius of the tire when mounted, and
loaded on the car.  This is NOT the same as the advertised diameter divided
by two.  One way to determine the rolling radius, is to park the car on a
flat level surface.  Mark the tire and pavement exactly where they meet.
Then push the car forward until the tire has made one exact revolution.
Mark the pavement again, and measure the length.  This is the
circumference.  Radius = Circumference / (2 * PI)

This will get your torque at the wheels.  For flywheel torque, divide by
the drivetrain efficiency.  If you want to know HP, then use the following
formula:

HP = RPM * Torque / 5252

Keep in mind though, that these formulas do not take into account rolling
resistances, wind drag, weather conditions, and other things that can
affect a "street dyno run".  So in actuality, real HP might be higher than
what you observe.  "Your mileage may vary", though.  :)

Brian

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