Help with PTO RPM calculation

[MHarryE]

Your calculations are right so the speed will be correct, but realize available power will be only a fraction of what you have at rated engine speed. For example, the chart for the engine on my L5740 says 57 HP at rated and 30 HP at 1500 rpm. That, of course, is before parasitics. If you tractor will handle it at the lower speed, fine. Our Ford 7200 has such a ePTO position but it can't be used for things like running our MoCo disc mower conditioner because of not enough power. It works fine for the tedder which uses a tiny fraction of the 80 available horsepower.

 

[Rock knocker]

Think again. Lots of tractors have multi-speed PTO gear boxes in them. My Yanmar 4220 had a 4 speed box, my LS has a 3 speed box. I think many tractors made outside of the USA and sold in Europe and other overseas countries have multi-speed PTO gear boxes.

I have been wrong in the past, so this wouldn't be the first.

 

[paulfun9]

Don't think so

:confused3:

 

[Rock knocker]

What's there to be confused about? I have already been corrected that these machines have a three speed PTO output.

I've stated I was wrong.

I now apologize and will take any more lumps.

 

[vsteel]

I don't agree that the same amount of fuel is used when reducing engine speed when doing the same amount of work. If the engine is running 1950 under almost no load and I reduce it to 1500 still under almost no load, there has to be an improvement in fuel consumption. This would be similar to a car shifting to OD when at cruise speed. The same work is being done but at reduced RPM so fuel is saved. Also there is less wear on the motor at reduced speed.

Cars are a different beast, they are very concerned about noise levels and vibration levels. Yes they are very concerned about fuel use and that is why they take into account things that can get them another .1 mpg. Also don't forget that almost all cars in the US are gasoline. Gas has a much smaller air fuel ratio window for combustion so it is less flexible to deal with the extremes in the power requirement.

Think of it this way, you have to use a certain amount of energy to get your work done. Fuel going into your engine is using that energy to do work. Anything you are doing at the PTO is still requiring the same amount of work so the only change energy consumption wise is at your tractor. You are still pulling the same load moving the same speed so that energy is constant. The only difference is how fast the engine is turning. What gains do you see with a lower RPM, less parasitic drag of the accessories but you are also farther away from your ideal engine RPM where it is most efficient. Every tractor is going to be different based on the torque curves and the gearing to get the 540 PTO speed. Go ahead and try it but don't expect miracles.

You will get a little less wear on the engine, but with engines rated at many thousands of hours, the economy setting it more about not having to listen to an engine drone as loud.