A lot depends on how you define "horsepower" whether talking SAE or NET or DIN. I remember some ratings that were more marketting than real (wind it tight, throw in the clutch, see how far the Toledo needle swings).
That said I wonder a bit if the Tecumseh (I know but not many posts on the other thread) is fudging a bit. For one thing it and the Chinese motors are both OHV, 3600 rpm, and the same displacement. An old saw in racing is "an engine does not care whose name is on the valve cover".
The other interesting thing I found was that there are no differences in specification published between any of the OH195EA engines whether 5.0, 5.5, 6.0, or 6.5 hp.
Third, both the 5.5 and the 6.0 have the same manufacturer's rating: 4.1KW. Assuming 30% loss this means 2.9KW continuous and a temporary surge (short enough so the flywheel effect is in force) to 3500 is reasonable.
Now without a lot of other specs (compression ratio, carb size, cam profile, valve size, exhaust restriction) but all are designed as fixed speed, long endurance engines so would not expect a lot of difference. All appear to be splash lubed, iron cyl linered aluminum engines so that is not a factor. All run on 87 PON gas so compression is not going to be high. I doubt that there is much difference in the generator IHP since all seem to be direct drive brushless.
In fact the only real difference I see is in the muffler and am working on that.
So before we talk about HP we need to know how it is being measured and by what standard. What I see is that all are the same displacement, same construction, same speed, and run on the same fuel so would expect the output to be about the same. I have not seen any mention of ball or roller bearing cranks, lifters, or high ringed hypereutectic pistons which would make a difference.
