Horsepower is the product of torque and rpm. So if two engines produce the same horsepower at different rpms, then the one that is turning at the slower rpm is producing more torque at rated horsepower. Folks talk about engines with a "lot of torque", but what they really mean is the torque curve: An engine with a flat torque curve will seem to have better pulling capability than one with a peaky curve, even if they're rated at the same horsepower. The reason is the "torquey" engine will continue to pull as the load increases, but at a slower speed, while the "peaky" engine will lose power and have to shift to a lower gear.
Fuel consumption is usually defined as "specific fuel consumption", which is typically described in units of "pounds per horsepower-hour". Two similar engines will have the same specific fuel consumption, even though their displacement is different. If the efficiency of an engine is increased, typically by increasing its compression ratio, its specific fuel consumption will decrease. So if you have two otherwise identical engines, the one with the higher compression ratio will have lower fuel consumption.
Another factor in fuel consumption is engine load. Gasoline engines have greatest efficiency at wide-open throttle, because no power is lost pumping air past the throttle plate. If an engine is lightly loaded, it will typically use more fuel than a smaller engine doing the same task.
In the case of the two tractors you're comparing, I'll bet the H has a much lower compression ratio than the 35. Of course, someone may have installed high-compression pistons in the H, which would make it more powerful and more efficient.
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Today's Featured Article - Grain Threshing in the Early 40's - by Jerry D. Coleman. How many of you can sit there and say that you have plowed with a mule? Well I would say not many, but maybe a few. This story is about the day my Grandfather Brown (true name) decided along with my parents to purchase a new Ford tractor. It wasn't really new except to us. The year was about 1967 and my father found a good used Ford 601 tractor to use on the farm instead of "Bob", our old mule. Now my grandfather had had this mule since the mid 40's and he was getting some age on him. S
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