There are always lots of varied opinions when it comes to the use of dynos; which make is best, why the readings may differ, how results should be interpreted, etc.
The best use for a dyno is for tuning and set up, and of course for before and after comparison of any performance changes that were made. Dyno shootouts are fun but it can annoy a lot of people if the dyno doesn’t show the power that they expected or were told by the builder that it should have. Just remember when you enter a dyno shootout, you are comparing one scooter to another scooter on the same dynamometer using the same standards or ‘reference’ and using the same gear. The dyno being used will not read the same as another dyno down the street. It is just a comparison, and your readings will vary.
BHP is not a true figure, but a calculation of the torque versus the revs. Therefore you can make an engine rev high, and get a high BHP reading, but unless the torque is high this power is not transmitted to the road. In fact you need to rev the engine more to achieve the same effect, so big BHP isn’t always big power. Always look at the torque reading, as this gives a more accurate idea of how well the engine is performing.
Also the curve of the graph is of utmost importance. Ideally it should be a steep rise then plateau out, holding the same power through the gears. A graph that rises to a peak and drops off quickly shows that the engine is producing max power only for a very narrow range. For example, different exhausts work better at different rev ranges, so the aim is to get the peak power at the optimum range for the exhaust and to hold that power through the gears speed range.
As stated, it is only fair to compare readouts on the same dyno by the same operator. Different people do things different ways, whether it be the tyre pressure or the use of straps, etc, that will affect the final reading. As long as the same operator performs your ‘before and after’ runs, you can then compare to see if any engine work has improved performance.
The other, and possibly most useful, tool for dynos is the lambda sensor, which will show you the air/fuel ratio at various speeds/revs. This is used to set the carburettor within the safe zone where the engine performs at its best.