Horsepower rating vs pulling power - 3039R vs 3046R

[ovrszd]

It's my belief that you will always notice the difference. Especially if the tractor is marginally under powered.

Is there a noticeable difference between the small V8 and the large V8 in a truck with the same drivetrain??

 

[TSO]

It's my belief that you will always notice the difference. Especially if the tractor is marginally under powered.

Is there a noticeable difference between the small V8 and the large V8 in a truck with the same drivetrain??

I think that's apples to oranges tho. As with the truck scenario, or even a tractor scenario with a gear transmission, those drivelines are putting direct engine power thru the driveline and to the wheels. It's different with a hydraulic driveline... The hydraulic pump and system relief dictate how the power is put to the wheels. I don't think my 1652 HST puts any more power to the ground than my 1648 HST did. And the 1652 has a much larger engine than the 1648 did (3.0 vs 2.2).

 

[ovrszd]

I think that's apples to oranges tho. As with the truck scenario, or even a tractor scenario with a gear transmission, those drivelines are putting direct engine power thru the driveline and to the wheels. It's different with a hydraulic driveline... The hydraulic pump and system relief dictate how the power is put to the wheels. I don't think my 1652 HST puts any more power to the ground than my 1648 HST did. And the 1652 has a much larger engine than the 1648 did (3.0 vs 2.2).

I can't agree. If your theory is true there would be no need for the larger HP engine.

My Brother had a L3240 Kubota HST. All it did was aggravate me. Gutless wonder. Same tractor in the higher HP versions works great.

Let's not complicate the issue by comparing gear drive to HST. That wasn't the original question.

 

[TSO]

Let's not complicate the issue by comparing gear drive to HST. That wasn't the original question.

Well you brought up a truck in the comparison ... I was referring to that.

 

[Ortimber]

My experience tells me that more horsepower will pull more even in a hydro machine. If you push the go pedal all the way to the floor on machines with different power, surely you'd start to stall the lower horsepower machine faster...

 

[ovrszd]

Well you brought up a truck in the comparison ... I was referring to that.

I should have clarified an AT. Figuring there's not one in a humdred members on TBN that daily drive a stick truck.

In regards to HST tractors. Less HP equals slower work when using them at or above 75% capacity. Idling around excluded.

 

[jmc]

All other things, besides POWER, being equal, either model will have the same push FORCE. That's controlled only by tractor weigh and the surface contact factors, like tread, studs, etc.

But more POWER will allow you to apply that same FORCE at a faster rate. One of the formulas for POWER is FORCE times VELOCITY.

So if "plowing better" is how big a pile you can push without slipping, no POWER advantage. If "plowing better" is plowing faster without stalling, more POWER wins.

 

[arlen4720]

There are many different viewpoints and opinions in this thread. I will attempt to explain how I think it actually works. I welcome any challenges to my logic. First some basic hydraulics...
The force exerted by a cylinder is determined by two things and 2 things only:
1) System Pressure
2) The cylinder's area
Not flow in any way, shape, or form. Normally the system pressure is determined by the system relief valve (at least in a gear pump system)

Now on to hydrostatic transmissions...
The OP's HST, like MOST HST tractors, has a variable displacement piston pump driving a FIXED displacement hydraulic motor. Like the pump and cylinder example above, the torque of a hydraulic motor is determined by:
1) System pressure
2) The displacement of the motor (how much volume of oil per revolution)

The notion that backing off on the hydro pedal increases torque or tractive force is false. When you back off on the pedal, you are destroking the pump which moves less oil. Since the characteristics of the motor are fixed, the motor spins slower. You are varying the POWER output of the transmission but the torque is unchanged.
So you can say that the hydro in a John Deere tractor is a constant torque type. The only way to increase max torque is to shift to a lower mechanical range.

Contrast that to Kubota's HST +...In addition to the variable displacement pump, the HST + has a 2 position variable displacement motor. I have not used one, but I can tell from looking at the hydraulic schematic that it would work great (still love my eHydro...How bout an eHydro +).
In the HST + transmission, you would actually get a nice torque boost when you shift the motor to the larger displacement position; just like shifting to a lower mechanical range.

Now that is cleared up, back to the OP.

The 3039r and 3046r all share the same range transmission, system pressure relief valves, and in fact the same eHydro tranny.
I think it is safe to say that the only difference is the engines.
The engine in the 3046r is going to be able to apply more input torque to the tranny, so in theory it should be able output more torque, right?
Not so fast...Chain both tractors to a tree and measure the tractive force, and both HST's will go into relief at the same pressure.
The bigger engine will of course behave better, be less likely to stall, move faster, and be more responsive. I think that would be noticeable for plowing snow.
If you are doing something like pulling out trees, I don't think you would see much difference, since you would be limited by traction. If you had lots of traction, both tractors would hit relief at the same pressure, exerting exactly the same amount of force at the drawbar.
I took the long way around because it seemed that there was some misinformation with the basics.
So what do you think?

 

[TSO]

We are in agreement...

There are many different viewpoints and opinions in this thread. I will attempt to explain how I think it actually works. I welcome any challenges to my logic. First some basic hydraulics...
The force exerted by a cylinder is determined by two things and 2 things only:
1) System Pressure
2) The cylinder's area
Not flow in any way, shape, or form. Normally the system pressure is determined by the system relief valve (at least in a gear pump system)

Now on to hydrostatic transmissions...
The OP's HST, like MOST HST tractors, has a variable displacement piston pump driving a FIXED displacement hydraulic motor. Like the pump and cylinder example above, the torque of a hydraulic motor is determined by:
1) system pressure
2) The displacement of the motor (how much volume of oil per revolution)

The notion that backing off on the hydro pedal increases torque or tractive force is false. When you back off on the pedal, you are destroking the pump which moves less oil. Since the characteristics of the motor are fixed, the motor spins slower. You are varying the POWER output of the transmission but the torque is unchanged.
So you can say that the hydro in a John Deere tractor is a constant torque type. The only way to increase max torque is to shift to a lower mechanical range.

Contrast that to Kubota's HST +...In addition to the variable displacement pump, the HST + has a 2 position variable displacement motor. I have not used one, but I can tell from looking at the hydraulic schematic that it would work great (still love my eHydro...How bout an eHydro +).
In the HST + transmission, you would actually get a nice torque boost when you shift the motor to the larger displacement position; just like shifting to a lower mechanical range.

Now that is cleared up, back to the OP.

The 3039r and 3046r all share the same range transmission, system pressure relief valves, and in fact the same eHydro tranny.
I think it is safe to say that the only difference is the engines.
The engine in the 3046r is going to be able to apply more input torque to the tranny, so in theory it should be able output more torque, right?
Not so fast...chain both tractors to a tree and measure the tractive force, and both HST's will go into relief at the same pressure.
The bigger engine will of course behave better,be less likely to stall, move faster, and be more responsive I wouldthat would be noticeable for plowing snow.
If you are doing something like pulling out trees, I don't think you would see much difference, since you would be limited by traction. If you had lots of traction, both tractors would hit relief at the same pressure, exerting exactly the same amount of force at the drawbar.
I took the long way around because it seemed that there was some misinformation with the basics.
So what do you think?

 

[4570Man]

It boils down to weight and traction. More HP is going to pull faster but has little to do pulling force. I’ll hook my 6 liter gas burner dump truck to a diesel pickup with double or 3 times the hp anytime. I can’t come close to pulling a load up hill as fast but they don’t stand a chance in a tug a war. If they’re not satisfied with loosing once we can try again with my 95 HP backhoe.