Why are tractors so under-powered?

[adventure bob]

Seems to be some confusion about duty cycle and WOT. WOT is not 100% duty cycle.

Duty cycle for an engine doing work is the amount of time it can spend at a rated HP. Remember that HP is simply torque (ft-lbs) Times RPM divided by 5252. HP ells us rate of work over time.
The duty cycle can either be varied by time or by work output. A 100hp engine rated for an 80% DC could be near constant use at 80HP or 100HP utilized 80% over the same period of time. The second would involve a series of use-rest cycles. In your POV, you are rarely at duty cycle, the difference being "drive cycle."

100% duty cycle engine is one designed to be run constantly at its rated HP (producing x amount of work per time). The figures you see in the pickup ads are the "max measured HP" Great for HP wars, not really effective at getting to how hard you can use it. Whats missing in the ads is rated HP not max HP.

In tractors and commercial rigs, the drive cycle and the duty cycle are closer together than n passenger cars and trucks.

 

[dodge man]

A good example of WOT and 100% duty cycle would be my Bx. If I'm driving down the road going as fast as I can I'm at WOT but the governor isn't wide open. When I'm mowing with the 60" MMM in heavy grass I'm also at WOT but the engine is also making near its maximum power because the governor is also wide open. You can also see this on the temp gauge, it will overheat if the radiator isn't clean.

 

[4570Man]

I can put my tractor at 100 percent power at WOT trying to pull a hill in high range.

 

[DavesTractor]

When can put a tractor on a dyno (we dyno all new tractors before delivery) and turn it to max PTO HP and it will run that way steady without overheating and without issue. Generally we test a tractor for 30 minutes, although we will normally lower the HP to about 75% of load. It is really rare for even a tractor to be truly at 100% load for any length of time.

I suspect if you took a new diesel pickup with 400 HP and did the same thing the cooling system could not keep up and you would probably burn through gallons and gallons of diesel.

 

[SteveM70]

When can put a tractor on a dyno (we dyno all new tractors before delivery) and turn it to max PTO HP and it will run that way steady without overheating and without issue. Generally we test a tractor for 30 minutes, although we will normally lower the HP to about 75% of load. It is really rare for even a tractor to be truly at 100% load for any length of time.

I suspect if you took a new diesel pickup with 400 HP and did the same thing the cooling system could not keep up and you would probably burn through gallons and gallons of diesel.

Interesting that you submit a new tractor to this. Have you had any engine failures as a result? As you are well aware there are different mfg. suggested break in methods and even more personal opinions on the subject.

 

[ishiboo]

Interesting that you submit a new tractor to this. Have you had any engine failures as a result? As you are well aware there are different mfg. suggested break in methods and even more personal opinions on the subject.

New engines run on dynos all the time... great way to break them in, tune them, etc. You don't put it on there and run it for 7 hours.

 

[SteveM70]

New engines run on dynos all the time... great way to break them in, tune them, etc. You don't put it on there and run it for 7 hours.

But isn't any amount of time spent over half throttle for the first 50 hours against some mfg. recommendations? At least it would have been on my Kubota.

 

[TomSeller]

But isn't any amount of time spent over half throttle for the first 50 hours against some mfg. recommendations? At least it would have been on my Kubota.

It may not be against manufacturer's recommendations but I wouldn't do it. Too old school I guess.

 

[DavesTractor]

New engines run on dynos all the time... great way to break them in, tune them, etc. You don't put it on there and run it for 7 hours.

Agreed. But Steve's point above is well taken. The point I was making was about putting a full 100% load on a tractor vs a pickup and how a tractor will handle a pretty heavy duty cycle. So I mixed that concept in with the comment that we dyno all our new tractors and I can see why there are questions. On a new tractor, we do not place a 100% load and just leave it, nor do we do a steady 75%. There is a warm up, then a varying load, a short time of heavy load, then back to a light load, a cool down etc. But I didn't want to muddy the thread with details that were off topic. I hope that helps clarify.

 

[adventure bob]

What Daves info tells us is that the HP rating of your tractor is its rated HP, not its max. I would think, knowing what I know about electronic engine control, that the ECU makes sure you never get anywhere near the peak HP. In a tractor the work I can do over time (HP) within its duty cycle is the measure of merit, not maximum HP achievable. So, the topic of this is "Why are tractors underpowered?" they may not be, they may just be using rated HP vice Peak HP which is what the OP compared the output to. The 60HP tractor in my barn may be rated at 60HP and electronically may not be able to go any higher, but it can run at 60HP all day long. My dodge truck peak HP is at 395, but could only realistically do that for about 10-15 minutes before bad things happened. Who knows, the trucks duty cycle may be closer to 100HP; Dodge however doesn't publish that data nor do the average consumers of trucks care. Tractor geeks care about how much HP over time can I sustain to accomplish work? Can I mow with a 15 foot batwing mower at 6 MPH and not overload my tractor for 4-6 hours of work at that level? Very different info than whats the max HP can my truck generate instantaneously?