Why are tractors so under-powered?

[ultrarunner]

I would say it is about balance and being designed for the intended task...

 

[gladehound]

Great title! Guaranteed to get a lot of attention! It's been beat to death at this point but since I'm writing I'll put it in one sentence....

Tractor are powered to maximize engine life for the type of duty cycle tractor engines typically see.

 

[Jim Timber]

And none of you has mentioned torque. :confused3:

Tractor's are tuned for broad torque curves, not peak horsepower. Getting 500hp at WOT and some super high RPM is just plain useless on a tractor if it can't lug a load up to full power. The intakes, exhaust, valves, cams - whole shooting match is tuned for quickly revving to make that HP on a street car because it's just not needed to carry it's weight for 95% of the time. On a tractor, as long as it doesn't take a minute to go from idle to peak power, not too many people care about the HP curve.

If you've ever looked at the Nebraska Tractor Test results, you'll see torque rise numbers, but not HP rise numbers. Torque is where it's at, and tuning an engine for torque is often not conducive to tuning for max HP.

Fuel economy is the other issue. Putting a 150hp engine in a compact tractor frame would mean you'd spin your tires and burn too much fuel. Not enough weight for the power to put it to the ground = wasted money all over. I can spin the tires on my 65hp utility tractor as it is. I don't need more power, I need more traction.

 

[MHarryE]

Comparison of some diesels. Kubota diesels are from the Grand L 60s lowest and highest HP versions. Caterpillar engines are from their web site. Matter of physics for the diesel cycle, more power per unit displacement as engine size grows - within limits. Comparing a small tractor engine vs a pickup sized engine is not a valid comparison. Marine vs industrial - marine applications are based on virtually unlimited cooling ability using the water in which the boat/ship is running. Something larger ag tractors today make use of is a power boost. A New Holland T7.210 for example is rated at 165 engine horsepower but has a 210 horsepower power boost for a short time. Its an equivalent of the marine engine unlimited cooling - through electronics the ag engine can make use of the higher power capability for a short period but the cooling system can't keep up for long periods.

1.8 Kubota 20.5
2.4 Kubota 25.8
4.4 Cat 39.8
7.1 Cat 43.1
9.3 Cat 49.0
7.1 Cat M 70.4 (Marine application, same basic engine as the 7.1 industrial above)

 

[gladehound]

And none of you has mentioned torque. :confused3:
.

I think that's because the OP already pointed out in the original post that the torque per liter (in addition to hp per liter) is also much lower in tractor applications than pick-up trucks.

- HP / torque characteristics are chosen based on a tractors weight and intended use
- engine is chosen that can reliably deliver HP/torque required by tractors weight and intended use
- Marketers then sell several models with slight bumps up in HP and charge big premiums for them because "everyone wants the best".

Interesting to note, that what is considered over powered vrs underpowered is often debated on TBN. Except people usually call overpowered tractors underweight! It all depends on the application. If you want to mow big fields and run the largest mower possible HP is important. If you want to push over a tree, gearing, weight, and torque are important.

This reminds me of a video I did once. My friend had a Toyota Echo (108hp) and thought it would out pull my 19hp tractor due to the superior hp. No chance. Anyway, watch the video if you'd like. Jeep Rubicon vs 19 hp tractor is also on there. It shows that for many tractor tasks, hp doesn't matter. (but for field work, more hp means more speed less time with same implement - I get that)

Kioti LB1914 vs. Toyota Echo and Jeep Wrangler (Tractor Pulling) - YouTube

 

[sd455dan]

I think that's because the OP already pointed out in the original post that the torque per liter (in addition to hp per liter) is also much lower in tractor applications than pick-up trucks.

- HP / torque characteristics are chosen based on a tractors weight and intended use
- engine is chosen that can reliably deliver HP/torque required by tractors weight and intended use
- Marketers then sell several models with slight bumps up in HP and charge big premiums for them because "everyone wants the best".

Interesting to note, that what is considered over powered vrs underpowered is often debated on TBN. Except people usually call overpowered tractors underweight! It all depends on the application. If you want to mow big fields and run the largest mower possible HP is important. If you want to push over a tree, gearing, weight, and torque are important.

This reminds me of a video I did once. My friend had a Toyota Echo (108hp) and thought it would out pull my 19hp tractor due to the superior hp. No chance. Anyway, watch the video if you'd like. Jeep Rubicon vs 19 hp tractor is also on there. It shows that for many tractor tasks, hp doesn't matter. (but for field work, more hp means more speed less time with same implement - I get that)

Kioti LB1914 vs. Toyota Echo and Jeep Wrangler (Tractor Pulling) - YouTube

Reminds me of working on a friends Ford 7.3 long box crew cab 4x4 F 250 that was almost impossible to start due to alternator and glow plug wiring issues, couldn't get it started to move it into the shop and it had been raining heavily for days.
Hooked My 55 Hp Rhino up and thought I would only lightly set the brake so- that it would tow but not freewheel roll. Had the Rhino in 2 wheel drive and just pulled the truck at an idle in 2nd gear from the yard to the garage.

Turned around once at the garage, and looked thinking it wasn't rolling (real) easy and noticed all 4 truck tires had pushed up almost a foot of mud in front of each tire- I hadn't checked closely and the truck was still in gear and in 4 low from loading it on the trailer. The tractors 14.9 28 R1s had not slipped a bit... and the diff was not locked either
Pretty sure the Rhino would also drag my 2003 Cummins powered Ram 3500 4x4 with out to much trouble as well, truck weighs about 8000lbs and the tractor weighs about the same as it was set up on that day.
Large loaded tractor tires and wheel weights with an aggressive tread make a bit of difference to.

 

[Jim Timber]

Not surprising at all Ron. :laughing:

I pushed a 20' bed rollback International (which had my 20' cargo container on it) sideways with my tractor in mud. He got stuck trying to turn around, then couldn't get the stinger to unstuck him, so I just shoved him with the pallet forks and dragged him with a chain. That trucks 9Klbs empty, and the container is 5Klbs. I couldn't lift it, but I can drag and shove it with ease.

 

[IH782]

Great title! Guaranteed to get a lot of attention!

Mission accomplished.

 

[motownbrowne]

If you even attempt to tune, kiss the warranty goodbye. Unless you can get the power to the ground without wheelslip, its pointless having it.

Mother Deere and other have been preaching for years, with these emissions engines it is better to go smaller and run maxxed than bigger that barely works. The emissions systems need maximum temperature to work effectively.

Yes, that's true. I certainly don't recommend that people do that, just that it's very doable.

 

[3930dave]

Comparison of some diesels. Kubota diesels are from the Grand L 60s lowest and highest HP versions. Caterpillar engines are from their web site. Matter of physics for the diesel cycle, more power per unit displacement as engine size grows - within limits. Comparing a small tractor engine vs a pickup sized engine is not a valid comparison. Marine vs industrial - marine applications are based on virtually unlimited cooling ability using the water in which the boat/ship is running. Something larger ag tractors today make use of is a power boost. A New Holland T7.210 for example is rated at 165 engine horsepower but has a 210 horsepower power boost for a short time. Its an equivalent of the marine engine unlimited cooling - through electronics the ag engine can make use of the higher power capability for a short period but the cooling system can't keep up for long periods.

1.8 Kubota 20.5
2.4 Kubota 25.8
4.4 Cat 39.8
7.1 Cat 43.1
9.3 Cat 49.0
7.1 Cat M 70.4 (Marine application, same basic engine as the 7.1 industrial above)

Great point about the thermal issues Harry.....

Rgds, D.