It has nothing to do with a lawsuit.
Here is an article that ran in the Washington Post
http://www.washingtonpost.com/wp-dyn/content/article/2008/02/15/AR2008021501732.html

Nevada,

I dont know if this formula is good for a diesel engine, but try this.

Torque= HP*5252
RPM

If you put the motor on a Dyno you can find out the Hp and torque.

The diesel your refering to would have max torque at a very low RPM. The Formula 1 racing engine would have a lot of torque, it just has to spin up to 8-9k to get to it. This is because of the short stroke in the engine.

I think this change has a lot to do with marketing. The average person has no clue what a Ft/Lb of torque is.
Maybe this suite came about from the same one to change the HP numbers on air compressors.

jon1, because torque and hp are not maxed at the same rpm, because not all engines are capable of doing both rpms, they are not proportional. Those big diesels cannot turn the rpms of an F-1 engine.

green_valley, reading that article it sure sounds to me that the lawsuits were at the very least the catylist in changing what is used for ratings.

Displacement for ratings works well also. There's an old saying, there is no replacement for cid to make torque.

Will they ever go back to HP? Don't know. The thing is consumers should get use to either looking for the highest torque rating or largest displacement for rotory mower use. Those numbers best reflect how much brute power the engine is capable of driving a rotory blade through the grass.

HP ratings were typically at 3600 RPM while mowers were typically governed to about 3100 RPM because of blade tip speed regulations.
The new Torque Specs are taken at 3060 RPM. MUCH closer to actual governed speed.
Note: this applies to typical walk behind lawn mowers. It DOES level the playing field for that purpose.
Deck design etc. still plays a very important part on how well a mower actually performs. My 20 year old Honda was rated at 4.5 HP, but it would out mow my brothers 6 HP Yardman when we ran them side by side in ankle/knee high wet grass.

If you ever want a good read. Read all the court reports in Ill. I got to read it at my job, talk about a big mess. I just love Briggs... What happans if Briggs started to produce cars again... I would buy a Kia!!!

At one time Briggs did make car bodies and many parts but they never made complete cars. At one time they made approx 90% of keys and locks for American made cars. But those days are long gone.

At the factory in Milwaukee they have what they call a car, more like a strange go-kart from the 20's that Briggs made and a small car [can not recall brand] which they removed the drive train and installed a apposed twin up front and battery electric out back on a captured trailer. This made it a 6 wheel car with the rear axle and wheels actually towed but inclosed within the body. Purpose was to not have the battery weight suspended from the cars suspension.
It was a early hybred and it and the little kart/car were both demonstration platforms, never intended for sale.

In an engine, horsepower is calculated from torque so how are they not proportional? Horsepower= torque * rpm/5250. Those big diesel engines do not rev high enough to generate those high hp numbers. Thats why that diesel making 550lbs of torque at 3000rpm is only making 315hp. Diesels only rev to around 2400-3000 or so rpm. Formua one cars rev to 18000rpms so they would not make a very good towing engine, likewise a diesel engine would not make a good race car engine. Now say i have a chevy small block 383 stoker engine going into a drag car making the 450lbs of torque but its redlines around 6500rpm. Assuming peak power came at redline, you would have 557hp. However if I built the same 383 stroker to pull a trailer and redline around 5200 rpm it would make 445hp. Obviously building engines isn't this simple as they are lots of other variables to consider like weight of the vehicle, gearing, tire size,intended use not to mention picking the right heads, cam, intake for your intended purpose.

I think you could drop an F-1 engine into a tractor, gear it down appropriately, and be just fine. If only for a short duration with frequent fuel stops.

den69 you are right about rpms which is why I say hp and torque are not proportional. Because peak hp and peak torque are not at the same rpm.

Small engines are hp rated at 3600 which where they max out for most applications and where peak hp is found. But peak torque is 2800 to 3300 depending on the engine. This works fine for rotory mowers because that is where they are governed to and torque better judges an engines ability to handle heavy loads. Here's the kicker, that engine max torque rpm which a rotory mower runs at, a 6 hp rate engine will only be make 3 or 4 hp.

Since the manufacture of the engine know where that engine is going when selling wholesale to the mower manufacture, sticking a 6 hp rating on it is false. It never will come close in its given application. But the torque rating is fairly accurate for its given use on a rotory.

If the torque and hp curve maxed out at the same rpm, then I would say they are proportiional. But they don't and because they don't the numbers get smudged in sales hype.

I think it would be a lot more accurate if they just used accurate Hp numbers. It sounds like they were fudging the numbers and got caught. Kind of like the shop vac that claim 6hp yet run of 110v.

I wonder if Honda and Kawasaki will use this rating system. Or is this designed to confuse the consumer so its harder to comparison shop.

Nevada point taken regarding how how the torque and hp curves are different. You will almost never ever have the same curve for both. However, my point is that a gas/diesel engine's horsepower figure is derived from the torque curve. Since engines do work by rotating, dyno's measure an engines torque and calculate hp from that figure. So in a engine, hp comes from torque so they are proportional.

I'm on the fence about engine manufacturers misleading the consumer. No one publishes chassis dyno results. In Nevada's case he used a lawnmower.

I'll use cars for example. Every car manufacturer publishes the engines max torque and hp figures at the engine. Car manufacturers used to publish gross hp/torque numbers for engines. This is with no accessories like fans/ac etc. They changed over to measure the net hp/torque with the accessories etc in the 70's and continue to publish numbers this way. The industry felt this is more accurate. However, your driveline ie transmission, rearend etc all take torque/hp to move with takes away from the engines total figures. I think driveline losses are around 30%. I agree with Nevada that if you want a true measurement, put you car on a chassis dyno to measure torque/hp which includes loses from the driveline. This is what we gearheads call rear wheel horsepower or rwhp. However, no car manufacturers publishes chassis dyno results so why should the little mower companies? There just following the rest of the industry. Why isn't anyone pointing the finger at Gm or Toyota etc?

I'm forgetting where I saw it but have seen horsepower ratings at the drive wheels on cars. I think the loss from drive train must be more then 30%. From recollection the weakest put out around 25 hp at the drive wheels and the strongest, those old big block asphault shredders, only around 55.

You make a good point regarding where power should be taken.It seems to me the power available at point of actual work rather then theorectical power derived from a engine only dyno would be preferable. This way the machines total efficiency in terms of power loss in transfer of power from engine to source of actual work gets rated.

What good is an efficient, powerful engine if its transfer to actual work is totally ineffiecient and saps more power then a total package which is more efficient. Matters not if we talk of cars or mowers. One might think a mowers transfer is simple and efficient but not really when really figuring it. Wheel/tires that roll easily with little restriction, blades with huge air lifts sucking power from its cutting action, drive system losses on self propelled models, etc.

Rating at point of work would eliminate much of the fudging on power ratings. A set under load standard could be set for rating testing. A mower could be tested under a simulate heavy grass and ground speed setting. A car would use the cars rated maximum weight load on a grade that would require full throttle without exceeding maximum rated rpm.

Mower engines have a governor to not allow more then a particular rpm. Under a heavy grass load the governor will allow full throttle if maximum rpm is not achieved.

Rating power in this way would be more complicated but would also be far more accurate.