the specs on my JD 850J with 6090 Powertech shows max hp at 1800 rpm and max torque at 1500 rpm. The operator's manual says to operate at 'high idle' (I call this WOT) which is almost 2400 rpm. Why run engine at rpms past your peak outputs?
My guess would be it requires the amount of fuel the pump is putting out at peak RPM to achieve those max. parameters...But again, that's just a guess
Rule #1. Horsepower can't be measured. It is a calculation derived from torque and RPM. 2400 RPM is called high idle because it is just that - idle. The engine will not be making much torque at 2400 RPM. As you apply load to the engine, the RPM will begin to fall and the torque will begin to rise until the RPM gets to 1800. This is peak horsepower. If more load is applied to the engine, the RPM will fall further and torque will increase (this is what's known as "torque rise", felt as the engine's ability to "keep on lugging") but because of the relationship between torque and RPM, horsepower will decrease. Once the RPM gets down to 1500, any more load will pull the engine down to stall.
Cmark, this was one of the clearest explanations of the concept I have ever seen. It makes me want to print it out and keep copies in my truck to hand out.
Thanks for the wonderful and concise explanation!
Ah, the awesome beauty of torque rise. What a pleasure it was to drive the old beasts with 40-50% torque rise curves. Could pull the pits of hell, inside out, with a long enough chain.
I bought a bunch of Matlack trucks when they went out, only 300 hp but the maxi-torque version. Would absolutely pull hell off the hinges, slowly.
Is that for a 3406 series engine? The literature looks older based on the logo styling, but I'm not sure what model this would have been.
Late 90’s 3406E
Old mechanical L10s wouid hang on forever as well. Most engines now are like a 12.7. Sees a hill and starts slowing down.
When I made my ignorant reply to the op I knew somebody would have the answer....but I wasn't expecting it to be Einstein.... I've always wondered what the relation was between HP and torque, You summed it up in terms even I can understand, Thanks.
I didn't like the L10 in equipment. It usually ended up in something like an excavator needing lots of constant torque and they then would make a ton of blow by and slobber all over everything. That valve cover was the worst. The problem carried over to the M11 models. Eventually they disappeared in the Japanese excavators and wheel loaders. They were an example of high horsepower numbers without the ability to carry the required amount of constant torque.
If you're doing lighter work, there's no problem to run it at 1,800-2,000 RPM. Something like a truck or old tractor, with a light load you can run at 1,500 where the peak torque is, the engine doesn't need torque rise because it has more "pedal" to make the torque, as long as you downshift before you lug it if you run into more load than anticipated.
No question is dumb, until it has been asked 25 times by the same person........
IMO, the L10 had no place in a variable load application except a truck. They did ok in tractors, but a 855 would still have been a better option. I never had a problem driving any truck with one. Better fuel economy than any 290 or 330, and you had more room in the cab for your feet.
The M11 in my dump truck is remarkably easy on fuel.