thanks to transmissions, the torgue is not the deciding factor. "Gears are torque amplifiers"...
A small engine that does 5 hp at 4000 rpms will do the SAME WORK as a larger engine that does 10 hp at 2000 rpms.. even though the larger engine has way more shaft power (TORQUE) at 2000 rpms. A two-to-one reduction gear system will put the smaller engine at the same exact shaft power. So
HP takes into account the total work you can get done in a PERIOD OF TIME with the help of gears.
Higher rpms means you can use gears to get more shaft power than with out the gears but you slow the work down the same ratio that you increase the power.
An engine that put out 2.5 hp at 8000 rpms will do the same work with the correct gears and weight as the engine that does 10hp at 2000 rpm.
Torgue is the shaft power of an engine with NO gears at a given rpm.
So with the correct weight so that the tires dont spin, and the correct gears, the higher hp/rpm ratio tractor will ALWAYS out pull every time.
AGAIN the most hp/rpm ratio will win a drawbar pull contest everytime if you have the correct gears and weight.
However....
higher rpm engines WEAR OUT exponitionally faster that slower rpm engines. if if you double the rpms, you increase wear by 4 times.
higher rpm engine use more fuel per hp. If I double the rpms, fuel usage will always be more than double. When you get above 2000 rpms the fuel usage can triple and quaduple for double the rpms.
higher rpm engines typically are more sensitive to load and will require more gear changes when conditions change.
higher rpm engine will develop much more heat per hp produced.. (see increased wear & increased fuel usage)
And Then,, if the hp is equal!!!!!! then the engine with the most torgue at lower rpms will pull better as the load changes and get better fuel consumption and gernally run cooler and last longer. this is why diesels of the same hp as gas engines will pull better as you increase the load and get better fuel economy. more torgue at lower rpms is the same as saying more hp produced sooner and lower rpms.
Then there is pulling a huge load ALL-DAY-LONG, YEAR-AFTER-YEAR, back to more torque is always better again.
Max fuel economy is achieved just below max torque.. Max hp is always a fuel eater..So for fuel economy more torque is better if hp is the same. In the 70's overdrives were added after the fuel crisis to keep engines nearer the max torque at highway speeds. Remember these engines had way more hp that needed to just drive 70 mph. The accidental result was that engine then lasted longer between overhauls. A gas engine that ran all day at 2200 rpm now started lasting as long as a diesel engine that ran all day at 2200 rpm. And fuel economy increased, oil stayed cleaner. Lower rpms and cleaner oil meant less wear.
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Today's Featured Article - Harvestin Hay: The Early Years (Part 2) - by Pat Browning. The summer of 1950 was the start of a new era in farming for our family. I was thirteen, and Kathy (my oldest sister) was seven. At this age, I believed tractor farming was the only way, hot stuff -- and given a chance I probably would have used the tractor, Dad's first, a 1936 Model "A" John Deere, to go bring in the cows! And I think Dad was ready for some automation too. And so it was that we acquired a good, used J. I. Case, wire tie hay baler. In addition to a person to drive th
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