edumacate me on horse power

[john_bud]

So you are saying, I could put a 21 hp gas engine in my tractor with the same gearing and same hydraulics with no difference in work produced?

I don't think so!

Yes HP is HP, it's just a number. The difference is how the HP is made. Which is stronger ?, something hitting a 33,000lb object up 1ft over a period of 1 min or something pushing 33,000lb all the way up to 1ft in the same 1 min.

Here is a link about where the formula came from.
What is Horsepower?

You don't think so? If you get a gasoline fueled spark combustion engine that makes the same HP at the same rpms as the current diesel engine, it will do the same amount of work. (Assuming that you match the weights of the engines)

I don't know how old you are, but in the 50's, 60's and 70's you could buy tractors of the same model with gas or diesel engines. Heck, you used to be able to get LP powered, gas and diesel all in the same exact model of tractor.

For example, 1963 Ford 4000 tractor could be bought with a 172 CID Gas engine or a 172 CID Diesel engine. Both 4 cyl - 3.60 stroke - 3.90 bore. Same basic block, head, crank, rods etc. Changes were made to accomodate the diesel with combustion chambers, compression ratios etc. But they were the same basic engine. They both were governed to the same RPM's even.

Here's the big question; Which one was able to produce more work?

I assume from your previous statements, that your answer would be the diesel, right? If so, WRONG! The gas engine made more HP and more torque across the entire RPM range. I can dig up a Ford dyno curve of both engines, but the ratings are 56.3 hp at 2200 rpm for the diesel and 62.6 hp at 2200 rpm for the gas. That basic difference was the same at all rpms.
The diesel was (and is) more efficient due to the increased compression ratio. Gas is 7.50:1 and the Diesel is 16.8:1.


jb

 

[RobertN]

So you are saying, I could put a 21 hp gas engine in my tractor with the same gearing and same hydraulics with no difference in work produced?

I don't think so!

Yes, you could and it would. We could pull your engine, and put the 21hp engine from my Farmall-A in it. You would have equivilant hp and torque. However, the Farmall engine is 113ci, your 21hp engine is probably 60ci or so. And, it would use more fuel. It is not that hard to build a good gas torque engine; all the tractors had them before diesel became economically feasible.

You could put a 21hp gas lawnmower engine it too. Here, the difference is, the toque and hp are at a definite "peak". If you are not at that exact rpm for that power peak, you lug like crazy. But, at the torque peak rpm, you'll have the same power.

Look at the venerable old Farmall Cub. It is still a popular mowing machine. It only has something like 10 or 12 hp GAS engine. It will pull a plow, disk, planter, mower... You can toss a finish mower on it, cut through grass easier than these 20hp lawn tractors, and if needed drag a lawn tractor around a field in a tug of war.

The Cub, like a Deere LA or other similar tractor, will have more displacement and use more fuel than a diesel. However, the engine is designed for torque, and definitely makes it.

 

[Champy]

The real issue being debated here is not true HP, but the application of that horsepower.

A diesel engine has much larger displacement and stroke characteristics that contribute to delivering a much differently SHAPED torque curve (powerband) for providing useful application of the HP being generated. Gas engines are smaller, lighter, and have significantly different torque curves that are optimized to provide a blend of high speed and reduced torque ratings.

A 25 HP gas engine will not provide the same output as a 25 HP diesel engine UNLESS their torque curves are exactly identical (along with gearing, transmissions, etc...). For that matter, this is why some 25HP diesel engines don't come close to other 25HP diesel engines - their output curves and delivery "systems" are not exactly matched for slope, peak, or durations.

 

[RobertN]

The real issue being debated here is not true HP, but the application of that horsepower.

A diesel engine has much larger displacement and stroke characteristics that contribute to delivering a much differently SHAPED torque curve (powerband) for providing useful application of the HP being generated. Gas engines are smaller, lighter, and have significantly different torque curves that are optimized to provide a blend of high speed and reduced torque ratings.

A 25 HP gas engine will not provide the same output as a 25 HP diesel engine UNLESS their torque curves are exactly identical (along with gearing, transmissions, etc...). For that matter, this is why some 25HP diesel engines don't come close to other 25HP diesel engines - their output curves and delivery "systems" are not exactly matched for slope, peak, or durations.

There are too many variables...

A diesel engine does not necessarily have a larger displacement. My Farmall-A makes similar power to my Kubota B8200. My Farmall is TWICE the displacement. It is a low rpm gas engine built for torque. It would have no problem pulling a plow or disc that my B8200 could pull.

Some gas engines, like the one in a lawn tractor are smaller and lighter. They also "peak" like a 125cc motocross bike; thier power band is very samll. If you fall out of the power band, you lose all power.

I would agree though, that comparing apples to apples has similar results, but most comparisons in this topic are apples to mangos

the beauty of the working power of a diesel is it delivers more power for less fuel per work unit, and delivers power across a wide range of rpm(typically; still there are purpose built engines)

 

[workinallthetime]

Im not going to get into this great debate over gas vs diesel or how to define horsepower. I will say get a 10 speed bike and ride up a hill in the highest gear then ride up that hill in the lowest gear. you will understand gearing and power to the ground after that. Power to the ground is all that matters anyway because thats where the work is getting done. My bx23 (23 hp) would not pull a maple tree out of the ground but my 300 hp gmc in reverse (lower gear) and in 4x4 low pulled it out, granted my neighbors thought i was crazy but the tree is gone. I always looked at things like this if you want to go fast get something with lots of hp if you want to work get something with lots of torque. Ill never own a diesel pickup truck and ill never own a gas tractor !!!
just my 2 cents probably not worth 1/2 that to some of ya.

 

[tallyho8]

My best friend owned a lawn tractor dealership for 38 years. He ordered some 17 hp lawn tractors from the factory. He received 15 hp lawn tractors. He phoned up and complained. They mailed him some 17 hp decals to put on the tractors and told him this was the only difference,

 

[john_bud]

I always looked at things like this if you want to go fast get something with lots of hp if you want to work get something with lots of torque. Ill never own a diesel pickup truck and ill never own a gas tractor !!!
just my 2 cents probably not worth 1/2 that to some of ya.

Huh? My 3/4 ton 4x4 diesel pickup has more than 300 hp, more than 500 ft-lb torque and gets more than 22 mpg at 70 mph on the freeway (empty). It has towed two trailers one 2000# and the other loaded between 8000-10,000 pounds for 43% of it's miles and has averaged 17.59 mpg since new. It replaced a 1/2 ton 4x4 gas truck with 290 hp, 300 ft-lb that got 18.5 on the freeway (empty). It towed the same two trailers for 28% of it's miles and averaged 16.48 mpg since new.

My truck and both tractors are diesel...
jb

 

[scott_vt]

I don't know how old you are, but in the 50's, 60's and 70's you could buy tractors of the same model with gas or diesel engines. Heck, you used to be able to get LP powered, gas and diesel all in the same exact model of tractor.

jb

Afternoon John,
Yea forgot distillate !

 

[638]

Something that has not been discussed is bore and stroke.

A long stroke engine will have more torque than a short stroke engine with the same displacement. A short stroke engine can turn at a higher RPM than a long stroke engine. Both engines may have the same horse power, but the torque curve will not even be close. The under square engine (longer stroke, smaller bore) will get off the line quicker, but the over square engine (bigger bore, shorter stroke) engine will rev higher between gear changes and generaly out run the stroker. This was my experience on motorcycles back in the 50s.

ron

 

[TrippleT]

Just for humor sake, horse power can be deceptive. Take a 25 horse Sears mower tractor, and hook a big mule or horse to it and see which one pulls the other off. As to engines there is not an explosion in the cylinders. The fuel burns and expands pushing the pistons down. If it exploded that is what it would do. Yes, is a very rapid process but technically that is what happens.