Well now I've gone and done it...

[Gravy]

If the engine rpm is the same, you will have the same speed as before.

If you want more speed, get larger diameter tires.

What you have is extra HP above what is required to power all pumps at maximum.

I don't think it's any faster at top speed, but it maintains any given speed with much less effort. The original engine did not have nearly enough HP to power all of the pumps simultaneously at maximum load. I think that over the years I have read that the tram pump needs at least 12hp at maximum rated speed & pressure, the main PTO pump needs 8hp, and the auxiliary PTO needs about 3hp. That adds up to about 23hp. No problem for a 25hp engine, right?


Well, not so much. The 25hp number is a maximum gross hp rating - or to put it another way, wishful thinking. The recommended continuous net hp for the Robin EH72D (and probably most any other 750cc class small engine) is around 16-18hp, which falls pretty badly short of the real power requirements. It's close enough that we can slow down and still get the job done, but it takes a good bit of skill and patience.

So far, the new engine allows me to be a good bit less impatient.

 

[Gravy]

The machines that are designed for slopes should have enough power to do the job at the advertised angle.

As your machine get work/older, it will not meet the specs.

I think some of you are asking the machine to do more than it is designed.

This is just my opinion, but why would you not designed for less HP for the pumps requirement, plus some extra.

Have you ever heard of 110 percent.

Maybe PT is not telling the full story. Like will my 425 climb a 30 degree hill with mower running full out and not stall?

I think this falls into the category of "6HP" air compressors that run on a 120VAC 15amp circuit and produce the same pressure and CFM as an old style 2hp compressor. In other words, the marketing department overruled the engineering department.

 

[KentT]

The pump would bypass based on pressure, not volume, so it has no real relationship to speed in normal use. It would bypass (if at all) in the irresistible force against an immovable object scenario, such as pushing a loader bucket into a pile of dirt or stone... rather than stalling the engine, you'd force the pump to bypass, or with my luck, you'd break something unanticipated -- such as a lift arm mounting point. :laughing:

 

[KentT]

I don't think it's any faster at top speed, but it maintains any given speed with much less effort. The original engine did not have nearly enough HP to power all of the pumps simultaneously at maximum load.

So far, the new engine allows me to be a good bit less impatient.

Exactly -- you cannot provide both maximum power (torque, based on pressure) and speed (based on flow) with the stock engines...

I would caution though, as Moss infers, that you might find other components of the PT's design that aren't designed to handle that much power. I'd never have imagined bending the QA plate, which I've now done twice, after upgrading the wheel motors. In both cases I was using reverse treadle to pull the minihoe backwards...

I've damaged my PT more with the minihoe than any other attachment because the 4ft boom magnifies stress, IMO...

 

[Gravy]

Makes you wonder if you had more HP available, and you did not back off the pedal as you would with the lower HP engine, would the pump be able to handle the added HP or blow up? Or bypass, I mean. Since none of us have apparently ever hit the bypass on the tram pump, lets add some more HP and push them till they bypass, then back off the HP. Right? :laughing:

I'm going with the theory that the pump manufacturers specifications are based on real continuous industrial horsepower, as opposed to the fantasy momentary peak horsepower advertised by small engine manufacturers. I'm not worried about the pumps. As long as the reliefs are working, they absorb as much power as they need and nothing more. The only way to blow one up should be to overspeed or overpressurize it.

 

[Gravy]

The pump would bypass based on pressure, not volume, so it has no real relationship to speed in normal use. It would bypass (if at all) in the irresistible force against an immovable object scenario, such as pushing a loader bucket into a pile of dirt or stone... rather than stalling the engine, you'd force the pump to bypass, or with my luck, you'd break something unanticipated -- such as a lift arm mounting point. :laughing:

Damage a lift arm mounting point, or rollover bar, or QA plate? Why, that would be inconceivable!

 

[Gravy]

I still haven't given the new engine a real workout, but I used the forks to move some stuff around today. That reinforced my initial impressions. For the old Chevy and Ford guys: 305 vs. 454, or 302 vs. 460. There is actual off-idle torque.

 

[KentT]

LOL... I'd forgotten all about breaking the rollover. That happened when I was running the 22ci Char-Lynn wheel motors and the minihoe. The 28ci ones are the ones that have caused serious carnage...

I think you'll find that extra power quite useful -- I'm envious@

 

[J_J]

Makes you wonder if you had more HP available, and you did not back off the pedal as you would with the lower HP engine, would the pump be able to handle the added HP or blow up? Or bypass, I mean. Since none of us have apparently ever hit the bypass on the tram pump, lets add some more HP and push them till they bypass, then back off the HP. Right? :laughing:

The pump will extract enough HP to do the job if the HP is available.

The relief valves should protect the pump if set correctly.

If you are not running all the pumps at maximum potential, you should hare spare HP available.

With more HP, you may prevent the engine/pump system from stalling, but the system will still relieve at the same pressure. You still have the same torque.

Larger wheel motors should generate more force, but you still need the HP. You should be able to do more work.

Your speed may drop, but you can counteract that by larger diameter tires.

 

[J_J]

LOL... I'd forgotten all about breaking the rollover. That happened when I was running the 22ci Char-Lynn wheel motors and the minihoe. The 28ci ones are the ones that have caused serious carnage...

I think you'll find that extra power quite useful -- I'm envious@

I don't understand the relation to the wheel motors and a cyl operating the rollover arm.

Now, if you buried the mini-hoe and tried to move the machine with valve lever in neutral, then the mechanical force on the cyl might damage the cyl, hose, or valve.

You need a crossover relief valve in that situation.