Gross HP vs PTO HP - HST vs Gear

[bmclernon]

I've always heard that HST cost +/- 2 HP. How does this affect the specs on lets say a 4110 which claims 20 Gross HP and 17 PTO HP? My 2210, which is HST, claims 23 gross HP and 17.7 PTO HP.

Is it possible to correlate these specs or are we in apple and orange country. In other words will a 4110 with HST have over-stated HP specs.

 

[cowboydoc]

Gross and pto hp are figured before anything external to the tractor is applied. When you consider hst, cabs, and other hydraulics and alternator drains it's all going to cost gross pto hp. A gear tractor will have more pto hp when applied than an hst tractor. The reason being that it's going to take more hp to run an hst over a gear tractor. To sum it all up say you buy a rototiller that needs 17.7 hp. You say ok I'll be alright my tractor can handle that. Well now get that tractor going at max pto and max work for the tiller in the ground and all of sudden your tractor starts to bog down and heat up. You wonder what the heck is going on. Well because of the hst and anything else running it's going to drain your pto hp. So now you are only making say 15 hp and you are 2hp deficient. You won't have overstated specs. Your tractor will run the 17 pto hp if put on a dyno but when you run the hydro it will cost you hp.

 

[JackIL]

Boyd,

The Society of Automotive Engineers (SAE) Standards on engine testing and reporting provide for 2 different conditions to specify Horsepower--Gross and Net. Gross is with all "accessories" removed from the engine. These include air intake and exhaust systems AND the cooling system so the number reported is extremely artificial and basically meaningless. However it is reported for the "brag" or advertising value because it is a larger number than the actual horsepower delivered at the flywheel of a fully functional operating engine. That would be the Net horsepower. This still does not account for supplementary pumps such as hydraulics or tractor accessories such as air conditioning on larger tractors. Note that both Gross and Net horsepowers relate to the engine only--the testing is done with the engine on a dynamometer with no tractor being involved.

The much more meaningful number to compare various tractors is PTO horsepower. It is the closest thing you will find to an "apples to apples test." This is measured at the PTO shaft of a complete STATIONARY tractor. Note that whatever hydraulic pumps are on the tractor are operating during the PTO power test (you can't shut them off), but they are in "stand-by" and not steering the wheels or lifting any loads. Even so these pumps require some power just to run.

Now in almost all tractors except tractors with hydrostatic transmissions, PTO horsepower is approximately 85 % of NET (flywheel) horsepower. For hydrostatic tractors it is usually around 83 % of Net. The reason is that it takes power to drive the hydrostatic pump even if the tractor is not moving. For tractor operations involving a lot of direction changing or needing very precise control of ground speeds, the hydro provides an excellent solution, but at a slight horsepower loss. Most current full-sized tractors that operate at steady field speeds don't need a hydro so a gear drive provides a better approach there. However, the infinitely variable transmission is now being introduced by almost all full-sized tractor manufacturers. It is a combination of gear and hydro elements. There is a slight power loss, but this is more than compensated for by the ability to get any travel speed desired to precisely match field conditions.

Now, getting back to your specific examples, if you go to the specs for the 4110 you will find that there are 2 different numbers quoted. For the collar shift transmission version, the gross horsepower is 20 and pto is 17 (85% of gross in this case.) However, for the Hydro version, the gross horsepower is 21! There has been some tweaking done, but they don't say how the extra power was generated. The PTO is still 17 (81% of gross). Finally for the 2210, the gross horsepower is 23 and the PTO horsepower is 17.7 (77% of gross). The NET horsepower is not included in the specs in the Operators Manual on line.

Both a Gear and a Hydro 4110 are rated at 17 PTO hp which is 0.7 PTO hp less than your 2210. I doubt that anyone would be able to tell the difference in real world conditions.

JackIL

 

[kennyd]

</font><font color="blue" class="small">( lets say a 4110 which claims 20 Gross HP and 17 PTO HP? My 2210, which is HST, claims 23 gross HP and 17.7 PTO HP. )</font>

FYI, in doing my research, I discovered that the 4110 and the 2210 have the same engine, but the RPM at witch the 540 PTO speed in reached is higher on the 2210. Basically they are running the 2210 at full throttle to gain this 3 HP.

Not sure that this helps answer your question,but I found it very interesting.

 

[art]

Cowboy Doc, no offence but I do believe you are off a little with your advice. If the main job for your tractor is PTO work that is where a hydro will out perform a gear drive by about a 10% margin from what I've witnessed over the passed years. If your main work is dead pulling the hydro is at about a ten to 15 percent disadvantage and then if at anytime you will have the troubles Doc is describing. Most compacts are going to have far more PTO work use then hard pulling and they work very well as far as manuvering other then the PTO work. We have found that the hydro's when properly maintained will out live about two to three clutch jobs at a minimum and at least one to two additional set of tires. The fuel used will nearly equal on PTO work but be higher on the hard pull use by about 10 to 15%. They hydro will allow you the comfort of never hearing a gear grind! The hydro's today with the foot petals drives act as a deadman petal so saftey wise they are the best for training drivers. In a nutshell Hydro's were designed for PTO work and have found to be great for tight manuvering.

 

[cowboydoc]

I don't see anything in your post that says I'm off? How can you say that a hydro is going to have more pto hp than a gear tractor? I don't get that at all. You put more power to the pto and the wheels with a gear tractor period. I've got tractors with 10 thousand hours and never had a clutch job. You don't grind gears with a synchro transmission. A non-synchro yes but we're not talking a non-synchro. I am not clear how you are saying you are going to go through more tires either? A hydro will rob a couple pto hp period. Whether that's a big deal or not depends on how close you are to the pto rating of the implement.

 

[art]

You talk of the hydro over heating! If that is the case then why are there no self propelled forage harvesters that are straight gear drives built! How about combines or self propelled mowers. Horsepower loss on the PTO mute when they easily out perform gear drive tractors hooked to the PTO. I'm glad to see you have good clutch life, not all people are that lucky. But then we have some hydro's out that have rolled the tach's a couple of times with no work other then normal maintenence on them too! When comparing identical model farm tractors other then gear vs the hydro's from the seventies the tire life doubled on the hydro's do to the fact of the cushion of the hydraulic fluid in the drive. Besides that if the airways are clean they will not over heat!

 

[Old_Hickory]

My hydro has never overheated and I really really work the tractor.

 

[cowboydoc]

I certainly didn't mean that only a hydro will overheat. ANY tractor, gear or hst, if you work it beyond it's capabilities for pto is going to overheat. Combines and self-propelled mowers are no different. You go too fast through too mcuh heavy hay, downed corn or beans, etc. and you are going to overheat. I also never brought up anything as far as reliability goes. The guy asked about hp loss. Just answer that question. The reality is you are going to lose some pto hp with a hydro over a gear. Jack who's a heck of alot smarter than me on this said the same thing. It isn't alot no. It's a couple hp or a couple percentage points but there is a loss period.

 

[jrlichina]

Cowboydoc is correct. A HST tractor will always have less available PTO horsepower for a given engine rating. You just need to make sure you pick the right sized tractor for your needs. If you think you are on the low end of your needs you should really consider a larger tractor. You don't want to buy a new tractor only to find out it will not run your implements like you expected. Go the next size up and be safe. As for your question, the ratings are what they tell you. You can't say a 20hp engine will yield 17.0 hp so 3 more hp will give you 0.7 more PTO hp when mated to a HST transmission. The actual PTO hp depends on the type of transmission it is connected to and how the PTO is designed into the transmission. Some designs are more efficeint than others. Bottom line, make sure the stated PTO hp is enough for your needs(future needs too!)