Quote:
Originally Posted by 1711Cub
I've never owned the WG600, but the same era Kohlers, which are rated at less HP have more usable torque than many modern engines. The whole HP rating for workhorse engines such as these is pretty useless IMHO.
|
It's not useless, and the modern engines (mostly) have just as much usable torque. Horsepower is a dependent variable of torque and RPM, and since they all run (and are rated) at 3600 RPM, definitionally the more horsepower the more torque at the desired operating speed of the engine.
The difference is the shape of the torque curve and what happens when you start lugging the engine down.
For a small engine in most of these applications, what matters is the torque rise i.e. how quickly the amount of torque increases as a function of decreasing RPM. The engines (at least the Kohler ones) are generally designed to operate well past the peak torque number so that if you get into a situation where the engine has to slow down from it's desired operating speed (3600 RPM), the engine can recover from it with increased torque output and bring the output back up to 3600.
The steeper that curve, the more "grunt" the engine has. A flat curve would mean that you're always putting out the maximum amount of force and the only way for you to maintain the speed you desire once the engine starts to slow is to reduce the amount of load the engine is under (i.e. slow down the work). You can see the commands have decently similar and probably slightly better curves than the K singles (the scale on the graph is different) and better than the D600, at least as long as you don't drag them down past the peak too far.
Here's the CH18/20/22 curve (for the 77mm bore engines). I'd consider these modern engines, as Kohler is still making them today.
For comparison here's from the D600 in the 882/782d/1512/1572:
And here's for the big kohler K series singles:
I've never been able to find solid curves for the M18/M20/KT17/KT19/KT21, but they are fairly similar to the CH18/20 from what I have been able to find, though maybe slightly "peakier". I agree that they would still compare favorably to the modern stuff in terms of power output, but probably not efficiency.
I don't have a graph for the WG600, but the numbers I found says it makes 30 ft lbs peak torque at 2450 RPM. If it's rated at 21 HP at 3600 RPM, that means it'd be making 30.6 ft-lbs of torque there. That's actually negative torque rise. It also means that if the power curve from the CH18 above is correct, the CH18 can actually grunt down and do what the WG600 could do if you had it pegged on the governor all the time and lugged down to 2400 RPM or so. The difference is that the WG600 can keep doing that work happily at 3600 RPM (i.e. more horsepower). You just can't load it down past that or it's gonna not be able to recover unless you back off what you're doing.
This also plays into why I think the diesel cubs are kinda pointless, at least in stock form. Add a turbo and turn them up or whatever and they are better, but they are pretty gutless in stock form.