HP vs HP

I am looking at putting a Wisconsin VH4D in a lawn mower that had an old 24 hp onan in it. The wisconsin has a lower hp rating than the onan, but more cubic inches. Is there a differance in the way they were rated? Please explain.

It may have to do with the RPM?
Zach

A VH4D was rated at 35hp when they were put in early skidloaders

Thanks, I could not quite understand the large differance from the other web site.
Thanks

Gross horse power vs net horse power ? They (SAE I think) changed to net HP back in the early 1970's. Also, checking out the torque those engines were rated for may tell a very different story.

horsepower isnt what does the work, its the torque that does the work ,for example cummins vs detroit, cummins 500 hp@1850 torque detroit 500hp@1650torque ,cummins pulls better every time and there both the same hp

Some HD engine companies post horsepower by full time sustained use, and not just max. power for a short time. That adds to the confusion of just Net versus Gross horsepower. Cars, light trucks, and lawn and garden equipment often use those inflated short-time max power specs.

Historically, engines sold for heavy duty use had specs posted for power they could supply 24 hours a day, and every day. Now, to compete, many post figures that are higher and based on high power for short periods of time.

Lawn and garden equipment has just about always posted power specs much higher then can be sustained on a full time basis. Recently many have been forced to lower the ratings. That's why you'll see engine ads now for engines listed as "formerly 20 horsepower" or something similar.

I don't know exactly how the difference in HP relates, but a VH4D ought to have plenty of power to run a mower. I had a Hesston self propelled windrower with an 8' header, and it ran it just fine.

Actually, it's the HP that does the work.

Torque is a measure of rotational force. HP is a measure of power, i.e., force per unit time.

Dean

Back to some basics. SAE=Society of Automotive Engineers-- peak horse power rating is at max rpm with minimal accesseries- as in no muffler, no aircleaner, no generators/altenators. DIN=Duetsch Industrial Norm (or something like that) and rates Horse Power as PS =(Pherd Stark) with all normal in use equipment. This is also a peak hp advertised but can have a working RPM rating. VW Beetle Engine in US advertised as 40hp is in Germany and many other countries a 35/36 hp engine or in some cases a 30hp engine when power to ground through transmission is included. This is similar to the wheel horsepower advertising that took place mid 1970s in US- the 200hp engines from previous year became 150/160hp engine with no change- a 20/25%drop from bare peak hp to actual working use equiped hp. The Onan may have a SAE rating at 4400 rpm without muffler and aircleaner- governor allowed to run to 4400 no load before limiting, the Wisconsin may have been rated at 3200 rpm as were many older small engines that were governed to run under working load at that rpm. Some of the older Kohlers and Brigges were governed and power rated at 2200 to 2400 rpm, some of the generator models were governed to 1800 rpm to get right electrical cycle. Check tag if you can find one on Wisconsin-hp rating probable notes rpm, at least the few old Wisconsins that had full tag remaining I"ve seen had the rpm noted for hp. If you check archives for nebraska test results most of the ratings will have the PTO or belt rating and the engine hp/rpm--as old JD B running at 1100 rpm and IHC H running at 1650. JD B had 179 or some such displacement (B had 2 engine sizes I know- green gang can post the early and late size), IHC had 152 inch or so, Hp ratings close to same, both rated 2 plow pullers. Have fun with engines. RN

Most likely. There is peak horsepower, continuous horspower, SAE, DIN and any number of ways to rate engines with and without accessories installed. You generally have to go to the folks who manufactured the engine to find out how it was rated. Standards have changed over time and the old rating methodologies are different from what is used today.
In short there"s no simple answer to your question.

Hello gary in canada,
Horse Power does the work. Power is work/time.
If you exert a force to move a load in a given distance, the result of you efforts has produced energy, which we commonly refer to as power.
Guido.

The VH4D is rated 30 HP at only 2800 RPM, while the Briggs and Kohler engines are usually rated at 3600.
Who told you the Wisconsin is less than 24 HP???
VH4D performance

VH4D IS rated 24 horse for heavy duty work. And, that used to be the way Wisconsin posted power specs, i.e. derated down to 80% for heavy duty continuous work. That 30 horse rating is the peak intermittent-use rating. They use that figure now to be more competitive with other makes who fudge the numbers.

not to be a pain but I believe actually SAE is the Society of Agricultural Engineers, they are headquartered in St Joseph Michigan.

ASABE = American Society of Agricultural and Biological Engineers - St Joseph, MI. Formally ASAE.
ASABE

When I was in college I put a brand new 16hp Briggs on a dyno. Peak hp was 13.4. I called the company and their reply was "that sounds about right". They let me know that they rate the engine at peak horsepower with no breather, no exhaust, running on special fuel (nitromethane maybe?) at around 5000 rpm. The factory engineer told me they only needed to hold 16 hp for a bout 30 seconds without blowing up to get that rating. I doubt the VH4D was rated that way.

Gary, it's the Cummins torque rise when lugged that gives it the "feel" of more power.
The two stroke detroits had a flat torque curve, no torque rise gained when lugged or torque lost when reved out.
That's why a Detroit two stroke will wail through the gears accelerating right to the redline without fading like the Cummins as it approaches redline.

I would like to thank everybody who posted with the great information and lively discussion. I will go with the wisconsin. Thanks

GOOD luck with THAT!

There's NO noisier, harder to start, bigger waster of gasoline, or just generally a MORE worthless engine then a Whisky! (Or more obsolete.)