Gross verses Net HP - what the heck?

[hayden]

The issue of "gross" verses "net" hp has surfaced. This is a new one to me. First, let's be clear that we are NOT talking about PTO HP, which is a measure of how much HP is available at the PTO after the rest of the tractor has siphoned off what powered it comsumes.

This started with the observation that, although one might expect the B2910 to have 29HP, is has 30HP. But the fine print says "gross HP", which in itself isn't too odd until you look at the literature for the L3010, 3410, 3710, and 4310. In the book they quote both Gross and Net HP (along with PTO HP). The Net HP corresponds to the tractor model number i.e. 30HP for the L3010, on up to 43HP for the L4310. The gross HP for each machine hovers around 10% higher than the net.

So what the heck is the difference between gross and net HP?

 

[Anonymous Poster]

There are 2 different Society of Automotive Standards used when quoting horsepower. Gross horsepower excludes the effects of the air inlet system (ducting and air cleaner), cooling fan, and exhaust system. It is sometimes called "bare engine" power since it excludes parasitic losses. Net horsepower is reported with the inlet air system, exhaust system, and cooling system in place and is the "usable" or "flywheel" horsepower of the installed engine. Obviously Gross horsepower is the higher number and, therefore, often quoted for advertising purposes. PTO horsepower is the power measured at the PTO with the tractor stationary and includes power train effects. It is the most realistic measure of power. In general for tractors, PTO horsepower is approximately 85% of Net Engine HP. With hydrostatic transmissions, the PTO hp is slightly less. As an example, for the JD 955 (hydrostatic), the Gross Engine HP is 35.3, the Net Engine HP is 33, and the PTO horsepower is 27.

 

[W5FL]

Jack says it well. Gross HP is a Marketing guys pipe dream. PTO HP can be used by an implement. Net HP is usable HP for the tractor.

 

[Anonymous Poster]

Gross Horsepower is like putting a roll of half dollars in your shorts before cruising the bars...

All show and no go.

 

[hayden]

Well - there you have it. Thanks

 

[gordon]

I must say that del defines it best on this one. I cracked up on that one del you do come up with some good ones./w3tcompact/icons/smile.gif
Gordon

 

[Anonymous Poster]

In the old days Gross HP wasn't even in the literature! I think we discussed this sometime back, where the next listing is "Theoretical HP" which is what the explosion of fuel "should" produce. This will please me greatly if Kubota issues the appropriate "40 T-HP" decals for my BX!

 

[Anonymous Poster]

It is not just the 2910 that quotes gross HP and does not list net HP. All the B-series tractors are listed that way.
What I find suprising is that the Carver web site incorrectly lists the B2910 at 29HP adding to the confusion.

Andy

 

[MChalkley]

Which sorta explains why they call it "gross" HP...

MarkC

 

[glennmac]

No comprende, due to lack of intellectual horsepower.

Why does all that air intake and exhaust stuff reduce the hp rating? If the the more realistic net hp is not measured at the pto, where is it measured at? At what pto is the pto hp measured--mid pto or rear pto or both?

I think Kubota has some sort of history of flipflopping between the various hp measures in naming its models. I think the current B series is basically gross hp, but that a series before that was net and before that was gross, or something like that.

Glenn