At the college where I retired from we had a Mustang eddy curent engine dyno, with electroic load control, and it would repeat within a couple horsepower if you keep an eye on water and oil temperatures for each run. And I could set the ramp rate to what ever I wanted, and by changing the ramp rate you could change the horsepower and torque readings of the same engine with no changes. And the Mustang was rated to 1,500 horsepower. But the unit at school cost $60,000 I got $15,000 in mine. Like I told the girlfriend, the Dyno is something I just always wanted and it is cheaper than a decent used car. Plus I should be able to sell it and get most of my money back one day.
I sure you know, but the reason the HP and torque change at different ramp rates is because you are using up torque accelerating the metal inside/attached to the engine. One way to get a "true" HP reading is a steady state test. Stopping at each test rpm and take a reading.
About 4 years ago, I was up at Superflow for a class and was complaining about this very issue. Short version is we talked to their engineers and they now have a inertia correction factor. Each engine is different and it's kinda a pain to setup, but when it's set it doesn't matter if the rate is steady state or 100, 300, 600 rpm per sec, the HP and torque give the same results.
Joe
PS so cool you built your own!!!
