something to add.
The newer lawn tractor will have compression ratio around 8.5:1 compared to the 8N of 6.7:1
Using proportioning and the 8N as a base case
and the ratio of engine displacements, rated rpm & compression ratios
HP(lawn tractor) = 20 HP (8N) x (49.8/119.7)x
(3800 rpm/2000 rpm) x (8.5/6.7) = 20 HP(lawn tractor)
where 49.9 = lawn tractor engine displacement 119.7 = 8N engine displacement 3800 rpm = rated lawn tractor engine speed 2000 rpm = rated 8N engine speed 8.5 = compression ratio of lawn tractor 6.7 = compression ratio of 8N tractor
Therefore, the lawn tractor measures up to its specs at 20 HP based on the 8N as a base .
If the lawn tractor and 8N are fully loaded that is putting out every thing its has, both machines will do the same amount of work in one hour, assuming the power train efficiency in each machine are equal.
However, in a tractor pull the 8N will pull the lawn tractor all around the barn yard!