If you can get your hands on an AC wall power-meter, in a few minutes you can get a good handle on how much power is going into your engine/cars.
Plug the meter into the wall outlet. Plug the Z-1000 AC power cord into the meter as shown above.
To be absolutely clear, this measures power going INTO the Z-1000. But it can be a hassle and expensive to assemble the instruments/meters to make accurate power measurements of what's going to the track.
With no load on the Z-1000 (nothing on the track), the meter says 8 Watts which is the overhead or idle power. Then I loaded the track with 10 Watts, 20 Watts, 30 Watts...etc. The chart speaks for itself. Reading the power meter Watts gives a good idea of how much power the Z-1000 is delivering to the track.
These power meters have come down in price recently. I got my no-name meter for less than $10 (free shipping from Asia) on eBay. The most recognized name in the US is probably the Kill-A-Watt meter - less than $20 at Home Depot. My public library even has them on-loan so you can check them out like a book!
P.S. A gold star to anyone who suggests the significance of the slope of the line. 
