</font><font color="blue" class="small">( Anyone have an idea what internal changes were made to up the HP or are 200rpm worth 2hp? )</font>
Here's a quick review of Force, Work, and Power that might help explain what's going on here. Force is a measurement of how much push or pull we're applying. Say you have a really big turkey sitting on your counter, and it weighs 55 pounds, then its pushing against the counter with 55 pounds of force.
Now, if you lift the bird up one foot, you will have performed some work, 55 foot pounds of work to be specific. Now power is a measure of fast we can work. Way back when, James Watt came up with a measurement called Horsepower. His definition is 550 foot pounds per second. So if you lift the 55 pound bird up one foot in one second, you'd be developping 1/10 Horsepower.
Now if you were able to lift 10 of those turkeys up at the same time 1 foot in one second, then you'd be developping 1 horsepower, because you'd be doing 550 foot pounds of work per second.
Now, if your not quite that strong to lift the 550 pounds all at once, you could still develop one horsepower, if you can be fast. To do that, you'd need to lift the 55 pounds up one foot in a tenth of a second.
With engines, we're turning the crankshaft, and the amount of twisting force we get is called torque. In fact, when you add those performance mod.s to your tractor, and then have it dyno'd, the dynamometer is actually measuring torque. Its typically measured in foot pounds, and there's a formula that lets you convert torque to horsepower, its:
Horsepower = torque * revs/minute * 1/5252
So, is 200 rpm worth 2 horsepower? It depends on the torque. Using the formula above, 200 rpm will develop 2 horsepower if the torque is about 52.5 foot pounds. I believe this is in line with the torque numbers for the engines you've listed. I have a diesel car, and it develops 90 horsepower at 3750 rpm. That means I'm getting about 126 foot pounds of torque at that speed. If I could get another 200 rpm at the same 126 foot pounds of torque, I'd get a boost of almost 5 horsepower.
Bottom line, there's something called the torque curve:
I borrowed the image above from
howstuffworks.com. When your idling, you're not making much torque. As you increase the throttle, the RPMs go up, and the the torque goes up. It's pretty rapid at first, but then it flattens out and starts to drop off. If you want to get more horsepower out of the same displacement, you need to try and make that torque curve flat through higher RPMs. To do that, you have to get more fuel into those cylinders. But you have to be careful, because more fuel means more force and more heat. Too much, and you burn a hole in a piston, or you break a connecting rod, etc. So, Kubota must have addressed these issues with their latest engine, and they've kept the torque curve up through higher RPMs
Hope this helps, and Happy Thanksgiving.
