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HP vs PTO implements

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perryjosh64

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I m sure it s a silly question but gonna ask anyway. Tractors have engine hp, drawbar hp and PTO hp ratings. I assume when looking to marry up tractor to a PTO shaft/implement you should be using "PTO hp" rating and not engine. With that said is it a safe assumption that store advertisements show required/recommended hp they are also using PTO hp ratings and not engine? For example I got a 64 Ford 2000 gas 4 cyl tractor w/4 spd trans. Believe it has 48hp engine and 31hp PTO. I should be using the 31hp to choose PTO implements or am I wrong?
 
PTO horsepower should be rated at the nominal PTO speed, 540 rpm in the case of your Ford. Engine horsepower is typically rated at maximum rpm. So the PTO rating will more closely match the implement's requirements than the engine horsepower rating. Does that mean your tractor can't handle a mower that supposedly needs at least 45 hp? Not at all; you can probable still run it but you may need to slow down your ground speed.

BTW, the Nebraska Tractor Test of your Ford says it put out 31 hp at 1900 engine rpm but only 26 hp at nominal PTO speed (540 rpm PTO/1484 engine rpm). Presumably both measurements were made at the PTO.
Ford 2000 Nebraska Tractor Test
 
Yes, the implement manufacturers use PTO HP to rate their implements...

With an asterisk *

* - The HP requirements of implements are almost always the BARE MINIMUM required to make them work.

Engine HP doesn't translate to the PTO the same way from tractor to tractor. Some have more loss in the driveline than others. PTO HP is the "common ground."
 
Just my opinion but I think the mfg's required minimums are high. They don't want to sell you an implement that will overwhelm your tractor and not
get as much work done as they promised. They'd have a dissatisfied customer. You can probably go 30% less than recommended and get by. I pulled my
JD 1207, 45 hp recommended, with a 3 cyl. 2000 and non-live PTO in third gear. It's probably around 28 hp.
 
I m sure I m WAY overthinking this and it s a habit to do so. Reason for questions is I was given an old 3pt post hole digger and the PTO shaft looks like it was assembled with spare parts and worn out so need a new one. Thing is want to get what I need/rated for my tractor/implement vs paying for an expensive PTO shaft rated for higher power.
 
With a post hole digger, your biggest concern will be breaking something when the auger gets jammed. Note that the piece you break might well be the tractor's PTO shaft, although your 2000 probably has an induction-hardened shaft. Picking an appropriate shear pin will protect everything. No grade 8 bolts for shear pins! Grade 5 maybe. Grade 3 bolts will likely fail before anything breaks, but you might find yourself spending more time replacing pins than digging holes.
 
I would not worry to much about the drive shaft on your post hole digger anyway since you are not going to use it at PTO rated speed. If you do you will have it thrashing around something terrible and will be breaking things. Just enough throttle to turn it is enough might better stall the engine than to break things from being wound up to PTO speed. With a bit of practice you will not break things nor stall the engine. By lifting it every so often as you dig it will also not become stuck in the hole as the dirt will sling out to the sides as it lifts. Don't lift completely out of hole and that will take a bit of practice also. just enough so the loose dirt slings off. In wet heavy dirt it might need to be done more than in lighter dirt. Dry dirt will sling off better.
 
You don't run a digger at pto speed anyway. Just off idle for me when using a digger, if there are problems nothing going to be hurt.
 
I have never paid much attention to ratings. The reason is that I own three Farmall M tractors. None have enough horsepower according to the ratings to power
a Land Pride 35-90 finish mower deck. This is the 7 and 1/2 foot wide model (90) inches. All three do a fantastic job at about half throttle. Ellis
 
Engine hp.... is the hp of an engine on a test stand.... with NO water pump, NO fan, NO generator/alternator, NO hydraulic pump, NO power steering pump and NO transmission load. This hp only exists on a test stand as will be less when loaded down in the actual tractor.

PTO hp is a REAL hp actually measured at pto shaft with all normal loads, fluids, and accessories installed at the rated pto rpm. Depending on which rpm its spec at, it could also be the real max hp of the tractor as delivered installed to the customer,,, or could be set at a different rpm for economy. No one plows with the engine on a test stand.
 
A lot would depend on the implement's purpose.

Some implements may require x amount of HP to work under normal usage.

Other implements may be designed to operate at x HP as a maximum for prolonged use without premature failure.
 
> What is the difference between belt and pto hp.

Well, belt hp would be measured off a pulley. Some tractors had the option of a pulley output in place of the shaft PTO. In the case of the four-cylinder Ford 2000, I'm pretty sure the nominal engine rpm when running a belt is higher than for PTO, so the pulley horsepower should be a bit higher than the PTO power..
 
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