How does the HP change?

[cumminstinkerer]

There's enough cars and pickups strapped down to chassis dynos to give plenty of evidence that automotive engines are putting out the power they advertise. (If not more - the latest Corvette ZR1 measured over 1000 hp at the wheels in an independent test, only about 30 hp less than the crankshaft rating. Drivetrain losses would be much higher than 3%.) And this makes sense because they dyno those engines (per the SAE J2723 standard) just like in the ag world - it is certainly not true that they use just theoretical numbers in their spec sheets.

Not wanting to argue but they sure used to, maybe they have changed their rating system.

 

[Mule Meat]

Torque and hp will change with an engine's state of tune of course. But the dyno measures torque and calculates "horsepower" based on the torque and the RPM it was measured at. Usually referred to as "rated" hp @ xx RPM- which is easily manipulated by the RPM the rating is taken at. Test the same engine at 2000, 2500 and 3000 RPM and you get three different "ratings". When you see the formula for calculating "horsepower", you'll see what the torque and horsepower curves always cross at 5252 RPM.
View attachment 144442
Horsepower=Torque (lb-ft)×Speed (RPM) / 5252

How does that come into play here? All of the engines show rated HP @ 2100 RPM.. Same with the rated PTO HP..

 

[Tramway Guy]

All of the engines are turbocharged engines. So all have different fuel settings, and perhaps other minor changes internally.

 

[ss55]

I picked up a JD utility tractor brochure. It lists 4 different HP for the exact same size engine. 2 questions: I assume the fuel is turned up to increase HP, yes? And, why bother buying the lower HP machine when cost is based on the engine size?

The power train are probably sized to match the horse power to stay price competitive in the market. Lower HP models might have different radiator, clutch, gears that are: thinner; lesser steel; or lesser heat treatment, narrower final planetary drives and smaller axles. Also compare the weights of the different HP levels.

 

[Sprint 6]

The one t

There's enough cars and pickups strapped down to chassis dynos to give plenty of evidence that automotive engines are putting out the power they advertise. (If not more - the latest Corvette ZR1 measured over 1000 hp at the wheels in an independent test, only about 30 hp less than the crankshaft rating. Drivetrain losses would be much higher than 3%.) And this makes sense because they dyno those engines (per the SAE J2723 standard) just like in the ag world - it is certainly not true that they use just theoretical numbers in their spec sheets.

Keep in mind, a dyno can be made to say whatever the operator wants.

 

[MeanGene1]

The one t

Keep in mind, a dyno can be made to say whatever the operator wants.

Dynos have adjustments or "correction factors" lol. Pretty common for different dynos to produce different readings for the exact same engine. And remember, the dyno measures torque, the actual twisting motion, and "horsepower" is calculated by torque and RPM, using the formula