Equivalent to a PipeLiner...
And when someone wants to compare it to a 20hp air-cooled, well, just walk away.
It seems odd that the ratings appear the same, but if you really want to know what the difference REALLY is, don't ask- just fire one up, put in a big rod, and strike your arc. Spend some time using it, get it set right, and really dig into a workpiece HARD... load it down, and when your rod is gone, change it quick, and bury the next rod. Do this continuously for half your workshift, and then pull it away, drag in the air-cooled twin, and do exactly the same thing.
After a half-hour, you'll fully realize and understand the difference.
These big boys were MADE to run 100% duty. The windings will stay cool, arc voltage is steady, and they'll eat welding rods 'till you can't hold'em any longer.
I've got several air-cooled singles and twins, and used many more engine-driven welders. When you get a machine that's compact, light, and powerful, you'll find things like aluminum windings, higher engine speeds, rattling tinwork, high fuel consumption, and oil burning tendancies prevail. Working 'em hard will cause windings to heat, brushes and commutators to burn and track, and welding performance gets weak. Heavier machines tolerate heavy loading better. Furthermore, they're generating a good chunk of usable AC power (again, continuous) to power worksite lighting, grinders, ventilation equipment, even air compressors... I can't ask that much of a Ranger 8, especially if I'm driving half-a-box of 1/8" 7018 through it with no 'rest' in between.
The crazy thing, is that these beasties are so CHEAP nowdays- that E-find was under $700. At that price, a guy could pour a little pad on the back side of the building, bring in an NG or propane line, hang a pair of good busbars across the shop ceiling, and use hook-sticks on short leads for universal shop welding supply... and in the wintertime, port the engine's waste heat into the shop for co-gen economy...