Right, there’s a lot of stuff going round about dynos. The power supposedly measured on dyno A vs dyno B…
Allow me to clarify. Power is a function to Torque times rotational velocity. Torque is a function of force times arm. Thus –> Power is a function of the MEASURED force, by means of a load-cell, times the distance of that cell to the driven axle (centre of the dyno roller), times the rotational speed of the dyno rollers measured on the dyno.
Not really clear, right?
Check the image to the right.
A load-bearing dyno is to be considered a tool for a tuner to calibrate the engine management system in such a way that it will perform as intended.
A lot of people expect all dynos to get the same result, they won’t! Due to a heap of differences, the most obvious being: single vs double rollers, type of eddy brake, load cell resolution, roller diameter, tyre slip, atmospheric differences, and so on! This is why VPR-Engineering won’t publish anything but the calculated power and measured torque at the wheels! No correction factor to approximate engine performance. There is no reliable way, except for a coast-down test, to determine drive-train losses.
And even with a coast-down test one could argue big differences due to tyre parameters changing during the test-cycle.
The only real way to measure engine torque (and thus engine power) is to put the engine on an engine-dyno!
It is a reliable way to measure the before and after effects of a tune, a hardware-upgrade, and so on. One does need to be a bit lenient with this as even strapping techniques or tyre pressure will change the measured torque, as it influences tyre deflection and thus effective radius.