520H vs HC Hydro

[1990Onan520-H 15]

Hey all, I'm doing somewhat of a restomod to my 90 520-H. Was just curious as to what the difference was on the H vs HC hydro. My knowledge tells me the HC was a bit faster (9mph vs the H's 7 mph) because the HC hydro pump ran at a higher pressure. If this is true, does anyone know what caused the higher pressure? Is it possible to take the H's hydro and change the valving or something to make it run as if it was the HC hydro, or is it a totally different pump?

 

TIA

[cleat 6,339]

Different gearing in the rear end and also the gear on the hydro pump itself.

 

[1990Onan520-H 15]

1 minute ago, cleat said:

Different gearing in the rear end and also the gear on the hydro pump itself.

 

So does the 520-H actually have a little more torque to the wheels then? I would assume it does since to go faster we would have to lower the numbered gear ratio.

[cafoose 3,355]

Check this out:

 

 

 

[cleat 6,339]

1 hour ago, 1990Onan520-H said:

So does the 520-H actually have a little more torque to the wheels then? I would assume it does since to go faster we would have to lower the numbered gear ratio.

If I am going to pull something heavy I use an H as you are correct in that it will have more torque

 

For mowing grass or plowing snow the HC is great 

 

 

 

[8ntruck 7,083]

In general, torque produces acceleration and pulling force, while horsepower and rpm produce top speed.

 

For a given amount of engine horsepower and operating rpm,  the belt and gear ratios between the engine and rear axle will determine pulling power and top speed.  More engine revolutions per axle revolution = stump pulling ability.  Fewer engine revolutions per axle revolution = higher top speed.

 

Hydrostatic transmissions usually use a variable volume pump driving a fixed volume hydrolic motor.  With the pump operating at low volume, there are more engine revolutions per axle revolution, like low gear in a geared transmission.  With the pump running at high volume, there will be fewer engine revolutions per axle revolution, like high gear in a geared transmission.

[Greentored 3,217]

I just went through this and studied, researched a LOT- @cafoose attached a link, thanks bud.

There are four gears that need to be changed inside the transaxle. The easiest way to go through all this is to visit the thread Cafoose linked, we got pretty in depth.

FWIW, I think the 520H will have PLENTY of torque even with the higher speed gearset.

I never finished this job due to an incorrect pump gear being shipped and lack of source for a new one thus far.  The other gears are sitting here waiting.