In Reply to: horsepower comparison posted by GregW on February 20, 2019 at 21:36:57:
Diesel engines have more torque at lower RPM than gas engines so it's a lot harder to lug them down to stall with a load. Using just my butt dyno a 30HP diesel seems to have a lot more power than a 30HP gas engine. Horsepower is horsepower so they should be equal, but the diesel will do more work and burn less fuel doing it. Another maybe more important variable for comparison is physical size and weight. If the compact diesel tractor is much smaller and lighter than the 640 you are used to, it probably will not seem to put the power to work as well. Smaller tires and less weight may not let you use the power effectively. If you can find something approximately the same size and weight, a 20HP diesel may be about equal to a 30HP gas tractor. Again, that is just based on how the tractors feel to me with no scientific calculations.
Sidebar discussion should be tires. Many modern compact tractors are being sold with type R4 tires. These appear to be a compromise between AG tread and Turf Saver. They may appear to be a good compromise but they actually have far less grip than regular AG tread tires. This will greatly affect how much power can be put to the ground with implements. The R4 is harder, wider, rolls smoother, and will last longer than AG tread if you operate mostly on hard pan and pavement.