Dyno results are completely dependent on calibration, just by changing one element of this you could get any HP figure you wanted from any engine. A dyno is only any use as a comparison tool. Even then many dynos will not give consistent results because the software does not edit the observed results properly. This is because in one important way the Honda engine responds differently to most other engines on a Dyno.
Dyno software is written to allow for atmospheric and temperature changes. That's why when you take a good engine out for a blast on a cold crisp morning you often feel like it is more powerful. That's because it is, due to the denser air and so on. Unfortunately, probably because of how it is cooled the Honda engine works in the opposite way, cooler air temp produces less power, hot air more.
So to get accurately consistant results from even one dyno you need one of two things. A temperature controlled dyno cell and or a very good experienced operator.
Next you have different types of Dyno involved. An inertia dyno times how long it takes to accelerate a big flywheel but a torque arm dyno measures how much force is required too slow the engine down. This means that some engine changes will have different effects. For example a heavier flywheel will probably show reduced power on a inertia dyno but more on a torque arm.
When I was first getting to know how different changes effected the Honda GX120, I kept a calibration engine untouched so that I could accurately compare results from different days.
Having said all of the above, if anyone still believes dyno's are all equal, I have a legal Honda GX160 that makes 15hp and I have the graphs to prove it. £3000 anyone!
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