Here's what I came up with.
Assumptions:
- I graphed snow blower HP required in 15" @ 3.5 mph for a given unit (let's say a 36" unit). I assumed it required 14 hp @ 3600 rpm and was linear.
- Engine 1 is my engine with 12.5 hp @ 3600 rpm, based on my complete swag at what the HP and torque curve might look like.
- Engine 2 is a more modern single cylinder OHV engine with approx 65% of the displacement of mine, putting out the same 12.5 hp @ 3600 rpm.
Right away I accomplished what I wanted to show. Look at this graph.
snow thrower HP vs engines.png
So say we have our 36" thrower and are moving forward in 15" of snow at 3.5 mph, full swath. As I said above, I guessed this would require 14 hp @ 3600 rpm. Neither engine has that. So follow the graph down to see what happens.
With engine 1, as the engine drops in rpm and power, the blower requirements also drop, until they match in the range of 2400-2900 rpm. So the engine will bog down under WOT (and the speed will also drop since it is all related), and things will continue at this lower speed and capability. You won't have to change the swath amount or your speed setting (as it will slow down with the engine).
However, with engine 2, there is no overlap at all. If you head into that snow at 3.5 mph, the engine is going to stall. There is no way around it.
Of course if you head into the snow at a lesser speed or take a smaller cut, to allow the thrower to require exactly 12.5 hp @ 3600 rpm, BOTH engines will perform EXACTLY the same. However, again, as you over load both engines and they bog down, the one with more torque will handle it better, but is still suboptimal. More torque just translates to more lower RPM HP and this is just the way it works in car and truck engines.
Theoretically you want to utilize all attachments while maintaining the engine at or very near peak HP rpm, to get the most work done. Which is why HP is important. But lower rpm HP is also important in real world conditions where it may be difficult to maintain the load at exactly what you want; the engine will be more tolerant of variations.