HST Power ?

[Hilbilly]

I recently traded my open station 47 hp Powershift tractor for a 49 hp HST tractor with cab. I love this thing but find there seems to be less power available. For most things so far it hasn't been an issue but yesterday I was using the boxblade to smooth out the driveway and thought there was a significant difference between the power of the gear tractor and the HST. The bottom of our driveway is about 15% grade and on the way down I could pull a full load on the 7ft boxblade in 2WD and mid range. On the way back up it was low range 4WD and struggling to keep the speed between 3 - 4 kmh.

Question is: if I had more hp would that improve significantly or is that just the sacrifice of having HST? I'm considering upgrading to a 60 hp HST from the 50 hp HST but don't want to spend a bunch more money and then find out there was not much of an improvement.

 

[jeff9366]

I recently traded my open station 47 hp Powershift tractor for a 49 hp HST tractor with cab.

I love this thing but there seems to be less power available.

Bear in mind a tractor cab weighs 600 to 700 pounds more than same model open station tractor. Your performance loss is more likely due to the additional weight of the cab than anything doing with the HST.

To notice a significant improvement pulling uphill with your Box Blade you will need at least 75 horsepower. Horsepower is always quoted at max performance but we seldom operate our tractors that way. You will NOT notice more than a minor improvement with an increase from 50 to 60 horsepower, assuming traction does not become a problem.

You should also research DRAWBAR HORSEPOWER for the tractor you have and the tractor(s) you are considering. Some tractor manufactures have 20% more efficient transmissions than others. Drawbar horsepower indicates "real world" pulling power.

Kubota is known for efficient HST transmissions but check yourself.

 

[MossRoad]

I recently traded my open station 47 hp Powershift tractor for a 49 hp HST tractor with cab. I love this thing but find there seems to be less power available. For most things so far it hasn't been an issue but yesterday I was using the boxblade to smooth out the driveway and thought there was a significant difference between the power of the gear tractor and the HST. The bottom of our driveway is about 15% grade and on the way down I could pull a full load on the 7ft boxblade in 2WD and mid range. On the way back up it was low range 4WD and struggling to keep the speed between 3 - 4 kmh.

Question is: if I had more hp would that improve significantly or is that just the sacrifice of having HST? I'm considering upgrading to a 60 hp HST from the 50 hp HST but don't want to spend a bunch more money and then find out there was not much of an improvement.

What make and model of tractor is it?
How old is it?
How many hours are on it?
Have the fluids and filters in the transmission been changed lately?
Things like that....?

 

[LouNY]

I recently traded my open station 47 hp Powershift tractor for a 49 hp HST tractor with cab. I love this thing but find there seems to be less power available. For most things so far it hasn't been an issue but yesterday I was using the boxblade to smooth out the driveway and thought there was a significant difference between the power of the gear tractor and the HST. The bottom of our driveway is about 15% grade and on the way down I could pull a full load on the 7ft boxblade in 2WD and mid range. On the way back up it was low range 4WD and struggling to keep the speed between 3 - 4 kmh.

Question is: if I had more hp would that improve significantly or is that just the sacrifice of having HST? I'm considering upgrading to a 60 hp HST from the 50 hp HST but don't want to spend a bunch more money and then find out there was not much of an improvement.

Thats a 10 Hp change some say thats not much, it's also 20% which sounds like more.
I believe that you would feel the difference but the hydro's have always sucked up a bit of horsepower.
And pulling up a grade with a load does take hp.

 

[CobyRupert]

OP isn't treating the hydro pedal like a gas pedal.....right?
(i.e. don't push pedal down more as tractor slows down, instead lift pedal for the "shift to lower gear" equivalent.)
He wouldn't be the first.

 

[ericm979]

HST tractors with linked throttle and HST pedal muddle that up even more.

When I am doing something ground engaging or going up a steep hill I set the throttle to PTO RPM with the hand lever and use the HST to modulate speed.

 

[ArlyA]

HST does rob a bit of your HP. I can't recall the numbers for sure and it depends on where you are in the power curve, but its in the 15 to 30% loss area. The higher percent loss is while doing max engine RPM and the HST maxed at the same time.

 

[Hilbilly]

Lots of good points / questions.

I forgot about the cab adding more weight. That combined with the bigger loaded tires adds about 800 lbs to this tractor and that's quite a bit. I recall adding that much to the 3PTH on the old tractor and noticing the difference.

The tractor is a 2015 1749 Massey with 230 hrs on it. I replaced all the fluids and filters when I got it and have put about 30 hrs on it since then.

I also thought that a 20% increase in power would be noticeable but maybe not. There's no way I can find out either since the dealers around here don't have anything I could try. The Massey dealer only has one tractor in the 40 to 60 hp class and it is the same one I have, just a year newer and the Kubota dealer doesn't have any tractors in that size.

Good points about the linked throttle and the HST pedal not being an acceleration pedal. It took me a bit to realize that the transmission needs higher rpm to work properly and to get the feel of using the HST pedal. When working it hard I have the throttle set at PTO rpms and monitor the tach to control the HST pedal position. When the rpms start to drop I back off the HST pedal until the rpms get back to PTO speed. It's a balancing act and I have that figured out.

 

[Hilbilly]

HST does rob a bit of your HP. I can't recall the numbers for sure and it depends on where you are in the power curve, but its in the 15 to 30% loss area. The higher percent loss is while doing max engine RPM and the HST maxed at the same time.

30% is a HUGE loss!

 

[MossRoad]

Lots of good points / questions.

I forgot about the cab adding more weight. That combined with the bigger loaded tires adds about 800 lbs to this tractor and that's quite a bit. I recall adding that much to the 3PTH on the old tractor and noticing the difference.

The tractor is a 2015 1749 Massey with 230 hrs on it. I replaced all the fluids and filters when I got it and have put about 30 hrs on it since then.

I also thought that a 20% increase in power would be noticeable but maybe not. There's no way I can find out either since the dealers around here don't have anything I could try. The Massey dealer only has one tractor in the 40 to 60 hp class and it is the same one I have, just a year newer and the Kubota dealer doesn't have any tractors in that size.

Good points about the linked throttle and the HST pedal not being an acceleration pedal. It took me a bit to realize that the transmission needs higher rpm to work properly and to get the feel of using the HST pedal. When working it hard I have the throttle set at PTO rpms and monitor the tach to control the HST pedal position. When the rpms start to drop I back off the HST pedal until the rpms get back to PTO speed. It's a balancing act and I have that figured out.

You say you have it at PTO speed. Have you tried it at higher engine RPMs? My late 70s IH2500b was HST. It had a hand throttle (like most tractors) that I'd set at PTO speed. And it had a foot throttle that I could give it more gas if my engine RPMs started to drop or I needed more power to, say, climb up a hill. Of course, I could also set the hand throttle for max RPMs as well.

So, again, I'll ask if you've tried it at higher engine RPMs than PTO RPMs.?

 

[oldnslo]

A good HST at full load is around 80% efficient. Like someone else suggested compare drawbar HP vs engine HP

For example our 5600 Ford had 69 Engine HP & 50 drawbar HP and this was manual transmission

 

[Hilbilly]

You say you have it at PTO speed. Have you tried it at higher engine RPMs? My late 70s IH2500b was HST. It had a hand throttle (like most tractors) that I'd set at PTO speed. And it had a foot throttle that I could give it more gas if my engine RPMs started to drop or I needed more power to, say, climb up a hill. Of course, I could also set the hand throttle for max RPMs as well.

So, again, I'll ask if you've tried it at higher engine RPMs than PTO RPMs.?

On this tractor they are pretty much the same thing. PTO rpm's according to the owners manual is 2500 rpm (there is no marking on the tach like my previous tractor) and the max I can get with the hand throttle is about 2505 or 2510. But yes I have pushed it to the max when working it hard.

It seems to me that the power loss occurs faster on this tractor than on the gear tractor but that could be the extra weight. The power loss appears to happen quickly with only minor grade changes. But that could be my memory or just due to the different way the HST responds than the gear drive. With the gear drive you feel / see / hear the power tail off as the hill starts to get steeper. With the HST I can keep the rpms up but have to watch the HST pedal position in order to maintain the rpms and watch the speedo to see how much speed I lost. There is less of "hands on" feedback with the HST. Just part of the adjustment process I guess.

I'm pretty sure that a 20% hp increase in a gear tractor would be noticeable but not sure if it would be with HST. I know there was a noticeable difference when I went from a 35 hp gear tractor to a 47 hp gear tractor. Especially climbing up the driveway, pulling the boxblade and using the 3PTH snowblower.

 

[MossRoad]

On this tractor they are pretty much the same thing. PTO rpm's according to the owners manual is 2500 rpm (there is no marking on the tach like my previous tractor) and the max I can get with the hand throttle is about 2505 or 2510. But yes I have pushed it to the max when working it hard.

It seems to me that the power loss occurs faster on this tractor than on the gear tractor but that could be the extra weight. The power loss appears to happen quickly with only minor grade changes. But that could be my memory or just due to the different way the HST responds than the gear drive. With the gear drive you feel / see / hear the power tail off as the hill starts to get steeper. With the HST I can keep the rpms up but have to watch the HST pedal position in order to maintain the rpms and watch the speedo to see how much speed I lost. There is less of "hands on" feedback with the HST. Just part of the adjustment process I guess.

I'm pretty sure that a 20% hp increase in a gear tractor would be noticeable but not sure if it would be with HST. I know there was a noticeable difference when I went from a 35 hp gear tractor to a 47 hp gear tractor. Especially climbing up the driveway, pulling the boxblade and using the 3PTH snowblower.

Interesting. My old IH had several hundred engine RPMs available above PTO RPMs, but it was a gas engine, so maybe that's the difference.

 

[Hilbilly]

Anyone know where to find Drawbar HP info? I Googled it and came up with some hits but none give info for specific tractors. I even tried a search for Massey 1749 drawbar hp and looked at TractorData.com but no luck so far.

 

[s219]

I think 15-20% is the typical power loss in an HST.

 

[WranglerX]

Kick up RPM to max specified operational speed in owners manual... With HST the speed and power (if shift lever is in high or low range) to wheels is regulated by HST pedal pressure not engine RPM let the HST do the work, it does not drive like a gear drives transmission....

Dale

 

[Motorboatin]

On this tractor they are pretty much the same thing. PTO rpm's according to the owners manual is 2500 rpm (there is no marking on the tach like my previous tractor)

You should have a line indicating the rpm required for 540 PTO rpm

 

[rScotty]

One thing that HST and geared transmissions have in common is that more gear ranges you have, the better match you are going to get for engine power vs load.
Our powershift only has 4 ranges and it never does seem to be in quite the right range. The HST+ has six, and can match power to the job much better in spite of having less HP.
rScotty

 

[Hilbilly]

You should have a line indicating the rpm required for 540 PTO rpm


View attachment 598080

My previous tractor had the same thing. A band of green showing the PTO range but this one does not. I haven't had a need for using the PTO at speed yet so I wasn't concerned about it. I checked today and found that the PTO revs are shown on the digital display. There is a button to toggle the display between PTO speed and the Soot level. Not sure what the right engine rpms are to achieve a PTO speed of 540 but I will find out some time.

As far as the proper engine speed for the HST, the owners manual states that the HST works best at 2400 rpm and higher.

One thing that HST and geared transmissions have in common is that more gear ranges you have, the better match you are going to get for engine power vs load.
Our powershift only has 4 ranges and it never does seem to be in quite the right range. The HST+ has six, and can match power to the job much better in spite of having less HP.
rScotty

Agreed. This tractor only has 3 ranges but I could certainly see the benefit of having 6. My previous gear tractor had 12 forward and 12 reverse. 3 ranges with 4 speeds in each. Low range was a creeper range which rarely got used. Pretty much all operations were performed in high range. Mid range was used mainly for hooking up implements and for snow blowing.

 

[WranglerX]

My previous tractor had the same thing. A band of green showing the PTO range but this one does not. I haven't had a need for using the PTO at speed yet so I wasn't concerned about it. I checked today and found that the PTO revs are shown on the digital display. There is a button to toggle the display between PTO speed and the Soot level. Not sure what the right engine rpms are to achieve a PTO speed of 540 but I will find out some time.

As far as the proper engine speed for the HST, the owners manual states that the HST works best at 2400 rpm and higher.



Agreed. This tractor only has 3 ranges but I could certainly see the benefit of having 6. My previous gear tractor had 12 forward and 12 reverse. 3 ranges with 4 speeds in each. Low range was a creeper range which rarely got used. Pretty much all operations were performed in high range. Mid range was used mainly for hooking up implements and for snow blowing.

Try pushing engine rpm up to near maximum (just below red line) .... That is where the horsepower is....

Dale