Well this is an entertaining read. my belief about different dynos providing different readings, whereby the difference is about 20% or so, I believe boils down to the difference of interpretation of the software engineer that wrote the code.
Power (kW) = Torque (Nm) x Omega (radians/sec^2)
Omega is angular acceleration
Omega = delta anguar velocity / delta time
So on the torque curve versus time the software engineer picks two points on the torque curve, which is never linear, in which to calculate angular acceleration, and this is where you can easily introduce big variation to give a 20% spread of power figures.
Also a good dyno should correct for:
Temperature - easy
Barometric pressure - easy
Moisture content - not so easy, and it makes a noticeable difference to the final power figures.
To measure moisture content correctly is a bit of a trick, and even back in 2001 when I was developing WRC engines, the dyno operators still did it the old fashioned way. I have never seen this done on any kart dyno.
Regarding RPM's dyno, I actually believe its an eddy current dyno, but am open to be corrected, to be honest I stopped paying any attention to RPM dyno figures about a year ago, as they re-calibrate by adding another 0.2hp every 4 to 5 months or so, so talk of motors producing 7.1mean hp does ring alarm bells for me, its probably to just sell more engines, as I haven't seen any lap records obliterated lately
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