Re: Mini Dyno

[Admin]

Well, all this information is all very nice but again, it’s all theoretical. By those calculations a 3.8 motor with 8.25 gears would go12.15 Kilometersper hour or 7.25 Miles an hour. I’ve had this set up on my WRX before and there is no way it was going anywhere near that fast.

If you wanted to go my theory, I made a dual cell bit charge that has double the voltage going to the motor wich means double the rpms at the motor which means double the speed. So, theoreticaly my WRX goes 24.3 Kilometers per hour or 14.5 Miles an hour? NO WAY, not even close. I’d guess my dual cell bit (which is twice as fast as my regular bit) might hit 4 Miles an hour just by guessing.

The friction of the gears without bearings (just plastic gears over metal shafts), friction of the motor rotor without bearings (just brass bushings), friction of the tires, friction of the axle in the plastic housing (again without bearings), friction of the front wheels without bearings (just plastic wheels over metal axles) all adds up in a BIG WAY. If a full sized human carthat was made without any bearings like these things are and with the sloppy tollerances magnified to larger scale you wouldn’t even be able to push it downhill. If you had a huge engine in it youwould probably only go 20miles an hour and all the points where there should be bearings would all seize up or melt away within minutes. Not to be funny but just to bring some reality to these numbers.

Finally, when the motor rotor decreases in resistancethe RPMs increase but the torque does not. That means the torque to rpm ration decreases. IF this ration stays the same you have a somewhat linear increase in overall power but when this ratio decreases, the friction becomes a greater factor in top speed. This means a car with a 1.0 motor might only go 50% of theoretical speed and a car with a 3.0 motor might only go 40% of theoretical speed (these are guessus of course but you see what I mean)

I’ve been trying to think of a way to make some sort of infared timing devise to set up and drive my cars through at full speed and calculate actual speed. I’m interested to see what actual speeds are.

Anyway, it’s always fun to crunch the numbers, Theoretical or Actual.

-Peter