Horsepower

[ford4ever]

QUESTION FOR THE TECHIES

When referring to horsepower in general do we look at pto or drawbar hp.Was looking up horsepower on www.tractordata.com

The site refers to engine power only for some tractors and then shows drawbar/pto for others.Is pto power the same as engine power .

Was getting the models ready for silage competition and looking to match age and hp

F

[fendt-man-matty]

boys a deere thats a quer and handy site been looking for something like that

cheers for putting it up

[powerrabbit]

Most manufacturers give horsepower specifications in the three catagories as engine horsepower is what the engine develops on the testbed at specific revs-per-minute. PTO horsepower is lower as power to the PTO is lost through the drive-train as a certain amount of power from the engine is used to operate the machine connected to the PTO.  Drawbar horsepower is what you have when the power is being put through the drive-train to the rear wheels. The three lots of horsepower quoted is what the tractor will develop as a maximum of each one. Some quote power in Kilowatts and if my memory serves me correct, one horsepower equals 46 Watts. 1000w = 1Kw.

[robbo]

Manufacturers hp ratings can vary wildly as it depends what standard the manufacturer chooses to use. Some take the reading at the initial output at the flywheel, with and without things like the fan, alternator and other ancillaries. Obviously that gives the highest possible readout of their tractor power.

Others use different measurements with ancillaries engaged which gives a lower reading. It gets even more confusing when you start to include features like powerboost which many tractors now have in transport or pto mode.

When you get your tractor dyno tested they are testing the pto output so don't expect it to be the same as the manufacturers rated output, very few, if any, manufacturers use the pto output as their rated maximum power, it can be up to 15% less.

Another interesting site is the Nebraska test lab which was set up many years ago to test the sometimes extravagant claims of the manufacturers

http://tractortestlab.unl.edu/

You might be surprised at the results for your favourite tractor although most of the tractors tested are American and may not be available in the UK

[allis8550]

British and European manufacturers tend to quote engine HP, while US tractors are more often quoted as drawbar or PTO HP. This can give quite a variation in figures for similar or even the same tractors. Add to this the different standards used by different manufacturers, ie. ISO or DIN figures and it becomes quite a minefield.

[britainswomble]

I'm not familiar with the ISO term for horsepower, but Ford's used to quote an S.A.E. and DIN figure. The S.A.E. is the Society of Automotive Engineers rating and is for a bare engine tested to maximum load. The DIN rating is, I think, a European standard for an engine fitted with all the items which may drain power when installed. PTO power is a useful figure to estimate how effectively it will power an implement, and will always be lower than either figure due to mechanical friction losses through the transmission. One of the worst losses was found on the Muir Hill range of tractors. As PTO drive went through a "Dropper" box; nearly 20 HP was lost on its way out the back. You will also notice that PTO horsepower at 1000 rpm will be higher than at 540 rpm for the same reason. 

[NIGEL FORD]

When we ordered our new 6600 in autumn '75 I asked for 2 speed PTO which Jimmy Starnes said we'd never use. But of course we drove a number of light machines much more economically at 540 on the thousand shaft at lower revs (about 1300 from memory) with adapter. After a few years I picked up a 3 metre ROTERRA that had only done 500 acres and still on its original tines for ?500 as no-one else seemed interested as it was 1000 RPM only. The 66 would have struggled to drive it if it was a 540 drivetrain but sang along for years with it no problem at all; well worth the extra ?90 odd quid investment on the new tractor spec. all those years previously.

Subsequently I found a pre-Q cab 7600 (at Wraights, Ashford, Kent) with 2 speed pto and put a new FIONA piggy-back drill on the Roterra for another few years trouble-free work, the 66 then became the loader tractor having swopped the Mil loader from the 4600, the 4000 having been traded in against the 76..... keep up at the back there...