Talk Morgan Forums Thread Like Summary - Performance measurement e.g. 4/4

Here is an article in German that is quite clear and well written, so a Google translation should provide understandable results. It is not too scientific but also not too superficial in its description of what to look out for when measuring performance on the chassis dynamometer.

Here is the link to the article
https://www.auto-motor-und-sport.de/technik/die-technik-moderner-leistungspruefstaende/

I noticed one sentence:

„The terms wheel power and drag power always cause confusion: Many people see the measured wheel power and therefore believe that this is the power at the wheel, but this is wrong. Vehicle and test bench form a single unit: if you remove the car from the test bench, the losses and masses are also removed from the test bench. For this reason, the wheel power on the dyno is lower - therefore the drag power must be measured in order to add it up“

If I understand correctly, the measurement is carried out by first accelerating and then measuring the force of the motor. But it is not only the friction losses in the drive train etc. that are involved, i.e. "in the car", but also the inertia of the rollers with their electromagnetic resistances etc. is also measured. As soon as the maximum power or the highest speed is reached, the clutch is disengaged and the friction is measured during coasting. This amount is added at the end to determine a plausible power value at the wheel. If I understand correctly, the 58 hp drag on the 4/4 is not the same as the effective power at the wheel on the road, which is higher?

Interesting question Heinz .... I've had cause to use rolling roads a fair bit but you can overthink it ... I use the same dyno with the same operator (Damien at Daytuner in Ripley for my racer 🙂)... absolute accuracy against some benchmark? ... whether there's a tiny difference in drag between one gear in a box or the next? .... I've just been interested in the comparison between what I had and what I've got after a remap after some 'improvement' I've made .... just a comparison to see if what I did put more power to the road or less ... the graphs are also useful for deciding optimum shift points and setting shift lights (and where to set your rev limiter to not lose anyrhing useful).

I've never needed to look that closely at absolutes ... if, as you say, they just lump the drag of the dyno in with the drag of the car parts then that would go a long way to explaining the variation between different power runs on different dynos (though I assumed there would be some process for identifying the drag of a particular dyno over a period of time and factoring that out of the final graph??) ... glad I'm only interested in comparative figures from one given dyno/operator ... I suspect there's a big can of technical worms waiting to cloud the issue if it's absolutes we seek 🙂

K

Ps ... and that's before we get into the understandable Human desire for a shop who fits go faster goodies to give the punter a graph that makes them happy 🙂

It's the opposite, a beam axle is more efficient than an independent rear end because there are no UJs/CV joints.