Is torque more important than HP?

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Old 08-14-10, 06:21 PM
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Is torque more important than HP?

A number of year sago, I could not believe my ears when I was told that our Farmall C tractor with the car-like inline 4-cyl. engine was only like 18 HP. I could not believe it. But I since do believe that is the case. Now there are lawn tractors, Say by Sears, that are 25 HP and have a 54 inch cut. My tractor by the way has a 60 inch cut.

The Farmall is governed so the rpms are relatively low. The rider tractors, on the other hand, allow you to turn higher rpm's.

Do you really think the 25 HP rider will outperform the Farmall, if apples to apples both are mowing at X miles per hour? I can mow through say 8 inch grass while tractor is in 3rd gear traveling at a good clip. Then again, maybe the Sears could also. Maybe I should have the next door neighbor with the very rider described come over for a cutting competition.

Does the Sears with the higher HP engine also have higher torque than the seemingly large engine Farmall? Or could the Farmal have more torque at the bottom end when rpm's are low?
 
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Old 08-14-10, 07:17 PM
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Originally Posted by ecman51` View Post
A number of year sago, I could not believe my ears when I was told that our Farmall C tractor with the car-like inline 4-cyl. engine was only like 18 HP. I could not believe it. But I since do believe that is the case. Now there are lawn tractors, Say by Sears, that are 25 HP and have a 54 inch cut. My tractor by the way has a 60 inch cut.

The Farmall is governed so the rpms are relatively low. The rider tractors, on the other hand, allow you to turn higher rpm's.

Do you really think the 25 HP rider will outperform the Farmall, if apples to apples both are mowing at X miles per hour? I can mow through say 8 inch grass while tractor is in 3rd gear traveling at a good clip. Then again, maybe the Sears could also. Maybe I should have the next door neighbor with the very rider described come over for a cutting competition.

Does the Sears with the higher HP engine also have higher torque than the seemingly large engine Farmall? Or could the Farmal have more torque at the bottom end when rpm's are low?
If you have a "C" Farmall, the question answers itself, it must be torque since, it has no horsepower and is at least 50 years old and is still working, probably aren't many high hp tractors that can say that. Old Farmall, Case, Allis Chalmers, Lawnboys, no power by todays standards, however they run and get the job done.
 
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Old 08-14-10, 07:44 PM
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Torque and HP are related numbers. Torque is the amount of work that can be done. If is typically measured in foot pounds here in the US. HP is determined by measuring torque at a given RPM. If you want to win a race you need HP or loosely translated the maximum amount of torque at the highest possible rpm. But any way you slice it torque measures your ability to extract work from an engine. If your 18 hp engine has the same maximum measured torque at 1300 rpm that a newer tractor has turning 3600 rpm, the new engine will have more HP. But the older engine will do the same amount of work - just at a slower rpm. Diesel engines are not known for turning a lot of revolutions but that is what goes into large tractors and pickups that are fifth wheel capable. Such engines are usually more fuel efficient under load because they are turning fewer revolutions. There are other reasons why diesels are better with loads - compression ratio of the engine and the fact that diesel has more energy than does gasoline.

A better way to compare that Farmall to a modern tractor is how much fuel was required for each to accomplish the task at hand?

Steve
 
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Old 08-17-10, 09:44 AM
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Today's big HP lawn and garden tractors have their max torque just about at their max RPM. The older farm tractors hit their peak torque before hitting their max RPM and have a longer (flatter) torque curve if plotted out on a graph. What that means is the older engines put out close to max power (torque) over a much wider RPM range than today's engines. Also need to consider the weight of the machines vs. work asked of them. Not so much for cutting grass, but that old Farmall C could pull a 2 bottom plow all day long because of it weight and traction. You can't do that with a 25 HP garden tractor, some of which can pull a single bottom plow, but not 2 and I wouldn't try it for a full day's work.
 
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