R4041/XR4040 Engine/PTO HP differential

nova3930 · May 22, 2014

GManBart said:
Not exactly. The engine HP rating is at "rated speed" which may be below the maximum RPM the engine can turn. The two are usually pretty close, but not always identical.

I'm wondering if the difference between the 4041 and 4040 is due to the larger displacement engine in the 4041, which could mean it has a flatter power curve...something along those lines.

Take this with a grain of salt because it's based on some guess work and extrapolation but I think that's exactly what's going on. I can't located the exact engine model numbers on either the Mitsubishi or Shibaura websites so I'm guessing on the engines used on both based on series and HP rating. The numbers on the R4041 are an extrapolated de-rate of the R4047 and the Shibaura engine data only went down to 2200 RPM so I had to do an exponential curve fit on the limited data and extrapolate down to 1500 RPM. All that being said, it appears the Mistubishi engines have a power curve that's a lot fatter on the low end, which you'd expect with a larger displacement engine.

BTW can anyone tell work is exceedingly boring today?

kingrace78 · May 22, 2014

Nice Graph. Why are tractors sold by HP not by torque. I would think torque would be more important than the hp.

jaydee325 · May 22, 2014

kingrace78 said:
Nice Graph. Why are tractors sold by HP not by torque. I would think torque would be more important than the hp.

Torque is the twisting force on a shaft. Torque gets a load moving.

HP determines how fast work can be done. Most farmers are concerned with how long it will take to get a field plowed for example.

So while an 18 HP steam engine may be able to pull a 500 hp modern tractor across the lot (I know there are other factors involved but bear with me). Torque (and weight) is a big factor here. The 500 hp tractor is wasting all its HP throwing dirt into the air.

Now hook a properly sized plow to each tractor and plow a 500 acre field. The 500 hp will get that work done in a fraction of the time.

Both specs are important. I also like to see the Hp/torque to RPM graphs as that can tell a lot about the characteristics of an engine.