Bapro is company that make dynos. Next to MAHA it is my favorite machine as this two brands don't use "standard" whp x 1.15 for calculating chp output (for fwd).
Thanks for the link and hint 🆙, I didn't know that company till I read your response. The specific Bapro dyno, you refer always, is it a load controlling or inertia dyno?
In general we see these two technologies, the load controlling brakes can be divided in different technologies: fluid types (water, oil, ...), eddy current and much simpler load suppliers. All those technologies have their purpose and application. But what all divide is the torque sensing system. Inertia dynos are the only one which are not having a force sensing system, they have a measured inertia and from the dyno roller speed change the torque can be calculated. All other systems are load controlled, that means for the moment of time or longer
, there is a force measured, either by a leverarm and a load cell which gives indirectly a torque = leverarm x force. For those load sensing technologies it doesn't matter if it is a eddy current type or a water type engine brake as it just put a resisting torque against the engine torque. At the balance point = no change in engine speed, engine torque (if mounted directly, else drivetrain loss has taken into account) and brake torque are equal, and only in that case the measurement can used like in the equation. If one run a non-constant speed program on the engine dyno the inertia of the dyno and engine increase the uncertainty massively as they are mostly not known, at least for the engine. Thence those engine or drivetrain brakes uses their own inertia, which only can changed in engine speed if an additional torque is supplied, which has to be added or subtracted (acceleration or deceleration) to the measured torque.
The engine inertia is for all measuring techniques, when measuring dynamically (increasing engine speed) neglected therefore dynamic measurements should always as slow as possible, which means at highest possible gear. And now I come to my point. Thence, and with what I've wrote above, all dynamic measurements for flywheel based calculations measure the a part of the inertia and the total of the friction by the run out measurement (gear in, clutch open, NO NEUTRAL!). From that we can calculate the engine speed related friction torque and a part of the inertia of the drivetrain.
My recommendation is measuring torque always stationary, which is the most accurate on the engine dyno and wheel horse power calculations. Anything else has always a neglected part of the inertia, which causes uncertainty. The guys who measure in 2nd or 3rd gear on the dyno to increase their flywheel based power figures know why they do it, but mostly you see it at VTEC, the torque jump is unreal high and short, just an oscillation of the roll, inducing a higher roll speed change, causing a overshooting torque at VTEC. OE's do power figures always stationary on the engine dyno, tune maybe on the chassis and street (idle can't be tuned on the engine dyno properly) to adapt the real system finally. That has a cause.
I was responsible for the uncertainties at the dyno, among other tasks, at the oldest engine company on earth. I introduced a process according DIN 1319 - the mother of all norms regarding uncertainty of measurements - for control of uncertainties in measurement, introduced torque sensing flange techniques as the water brakes and generator are too huge in their uncertainties, dynamically and stationary. The approach I developed, was rolled out for the hole company, which has over 30 test benches (1.2-2.5 million Euro each) all over the world. Every test bench cost 3000-10000 Euro (biggest engine has 13,600 flwhp) a day in fuel and supplies, definitely worth to focus on some essential sensors at a cost of a few 1000 Euro/year for recalibration. How does this look like in the tuner scene 😆? But I understand, they all need to feed their families. That is the cause I tune 99 % on street, the street has it's own rules, but as you know it, the street supplies a very good brake, and that is what tuning needs. The measurement is just last step for number and maybe IGT confirmation, but for most tuning tasks you don't need the dyno. Beside that, it is too expensive for many, last step = tuning, last money dried out before tuning, tuning budget = wifes annual present, which is declined for that year
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