Those aren't dyno number, just crank numbers. Dyno numbers on most of those cvt shaft driven bikes will probably be close to half that number

 

True, and the ones starting off with a hp handicap also loose power to the wheels, so things do not change as much as you think.

A 680 big bore should really not be sitting at the bottom of the hp list with mid bore displacement ATVs.
But OHV have a rpm disadvantage vs a OHC.

Last I read is the 376cc is 24-25 hp.

 

HP for an engine is measured at the crank on an engine dynamometer; in
a vehicle, it is measured on a chassis dyno.

I wanted to know are TLC's numbers from a maker's statement or some
publication, so I can go and check them, and see if others are also
published, and how they were generated.

 

Well as far as I know, TLC chart is 100% correct when it comes to crank numbers. It's been posted around a lot on the web, I've seen it about 20 times myself. Of course usually people don't cut the rubicons 34 hp number from the chart lol. That a 1 cylinder, 500cc ohv engine putting out the same as a Polaris 500cc SOHC.

 

There was a horsepower chart like that going around supposedly from the California Air Resources Board (CARB) but I went to their website and couldn't find it.