HP ratings of small engines

[Gary Fowler]

It seems now days a garden tractor or lawn mower needs 25+ HP to pull a 42" deck. I can remember in the 70's that riding lawnmowers rarely had more than 12-14 Hp and pulled at least 38" mower really well. Have the engine manufacturers went to a different rating system for their power ratings. I have a 1987 model JD 332 diesel with 16 HP rating that pulls a 54" deck without a problem but I need 26 Hp on my ZTR (gas) to pull 52" deck under same conditions. Whats up with these engines now.

 

[jenkinsph]

Gary,
I see it as a multitude of issues, marketing knows that listing a higher hp engine is a plus to most buyers and cost the manufacturer very little eztra money. Another thing is the speed at which the machine is moving, faster machine needs more power to operate. Lots of issues the last few years with the hp ratings themselves, most have switched to posting the torque specs instead after lawsuits. Hydrostatic systems have higher losses than the early gear drives so a little extra power needed to compensate for this.

I think most of the riding mowers and garden tractors have more power than you really need, I know my L130 gas and X749 diesel mowers don't bog down enough to hear it.

 

[bilrus61]

People are so much fatter these days over the '60 and '70 the lawn mowers need that extra ten horses just to lug the rider around the yard. The mower still uses the same power for the same width deck but put a year 2011 guy in the seat and a bit of a grade to the yard and it becomes obvious why they had up the horsepower in todays mowers.

 

[cmhyland]

I had a 1971 Cub Cadet Garden Tractor. It was 10hp.
It ran a 48 in deck and a 36 in rototiller. it would run a 42 single stage snowthrower...As far as needing more hp to haul hefty riders, a new 25hp lawnmower weighs 300 lbs... My 10hp Cub Cadet weighed about 750 lbs... It actually had the same trans and rearend as a farmall cub.

The new "Lawnmowers" seem to be built as a throw away... If I had an acre or less of lawn to mow, I'd buy a commercial walk behind...

Regards,
Chris

 

[Ford tractor]

There was a lawsuit about the HP ratings being 99.3% fiction and 0.7% marketing a few years ago. Now most push mowers are rated by the displacement. Seems the mfg's were all allowed to "estimate" HP. When sales were down, the HP grew the next year. Since the displacement, carb, and compression were identical -- I wonder how they did that?

 

[Short Game]

The lawn mower class action suit covered nearly every brand and many thousands of customers got checks from the companies. They lied about the HP and got caught that time. I'm sure the payout was a fairly small portion of the profits made, so probably no one got hurt very bad. They most likely got a bit more back out of creative tax write-offs.

 

[Skyssx]

The love affair with MULCHING! has a lot to do with needing more HP. Belts also lose you about 15% of the HP right off. Not sure how much a pure gear based PTO loses, though.

I swear. The number of people blowing belts this year because they were mulching 8" wet grass was astounding.

 

[fuseboxer]

I got three checks for over rated HP on garden tractors<JD> and one for a Cub cadet. The engineering spec in not to reflect a Peak HP but an American engineering standard. Horsepower sucks gas and the more HP the more gas. They did me a favor when the gave me 23HP Mowers and claimed they were 25HP. With a 100 million mowers in the USA that saves a lot of gas. Truth is we could get by with a lot less HP and torque. Remember the old 8N/9N and others only had about 24HP and good torque for a two bottom plow. People made a farm living with them. Shure beat the **** out of the mule my brother in law plowed with.

 

[Gary Fowler]

I seem to see the same in cars and trucks. I had a stock 351 Clevand engine in a 1970 Ford Torino that supposedly had only 275 HP but would smoke the biggest tire made at the time and hide the needle (120 MPH) in less than a half mile, over 85 MPH in a quarter mile and now we have 4 cylinders with claims to that much hp and more that wont do half (well maybe half) as much in performance. I could also get 19 mpg running over 75 miles per hour with that Torino but that was with real gas at over 100 octane. The book said not to use anything less than 101 octane. I sold it in 1974 because I could no longer get gas at the pump that wouldnt knock. I just dont believe most of the HP ratings that come out with any motorized vehicle now.

 

[Skyssx]

Tires are exponentially grippier now than they were in the 70's. Not only that, but your 275 1970 horse power was more like 125 by today's measurement. A new Rav4, a grocery getter by any sense of the word, can do 0-60 in 5.7. That's faster than a 1990 Ferrari.

Being able to just melt tires in a RWD with 125 HP and having a FWD econobox with nearly 300 HP being unable to do so really shows how far the technology has come.

 

[LD1]

When it comes to lawn mowers, it is about blade speed and ground speed.:thumbsup:

Those older mowers that didnt have the HP, couldnt match the ground speed of todays mowers, especially ZTR's.

Even the riding mowers with 26HP and ~52" decks can still get a good quality cut without lugging too bad at a MUCH faster ground speed than the older mowers. Problem is most peoples yards are too rough, ot they just dont ever try mowing in a higher gear.

 

[oldyellr]

I seem to see the same in cars and trucks. I had a stock 351 Clevand engine in a 1970 Ford Torino that supposedly had only 275 HP but would smoke the biggest tire made at the time and hide the needle (120 MPH) in less than a half mile, over 85 MPH in a quarter mile and now we have 4 cylinders with claims to that much hp and more that wont do half (well maybe half) as much in performance.

Over the years, car manufacturers lied both ways about horsepower. In the 1960s they grossly exaggerated horsepower, but when GM made the 302 engine for the Z/28 Camaro, they only called it 295 hp just to pacify the insurance companies, even though it could put out 400. The auto industry have always been shysters about horsepower and performance. You also must realize that automobile engine horsepower is measured at the flywheel with no accessories. All the accessories and a slushbox transmission eat up a lot of that before it gets to the drive wheels.

Things like outboard motors, tractors and mowers have been a lot more honest about horsepower over the years, until, of course, the marketers figured they could gain an advantage by lying, leading to the class action suit.

 

[oldyellr]

Being able to just melt tires in a RWD with 125 HP and having a FWD econobox with nearly 300 HP being unable to do so really shows how far the technology has come.

Well, you won't really find an "econobox" with 300 hp, but a Subaru WRX or Mitsubishi EVO will give a Corvette a good run, but you have to know how to drive and keep it in the narrow power band.

A tractor engine is completely different. It needs a very flat horsepower and torque curve so the governor can react to any increase in load without losing RPM.

 

[scrappy isb67]

alot has to do with the engine.
Dad has a 982 that has been re-powered with a 25 hp V-twin and it pulls down in heavy grass. My deere has 1 hp less and doesn't pull down unless I am trying to break the mowing speed record in HEAVY grass and I am running the same size deck as he is

 

[BethesdaEC]

Well, you won't really find an "econobox" with 300 hp, but a Subaru WRX or Mitsubishi EVO will give a Corvette a good run, but you have to know how to drive and keep it in the narrow power band.

A tractor engine is completely different. It needs a very flat horsepower and torque curve so the governor can react to any increase in load without losing RPM.

Car engines rarely spend a significant amount of time wide open throttle, mostly they are rolling down the highway at 2000 RPM putting out maybe 20 HP. A mower spends it entire life at WOT putting out max power.

 

[Will_C]

I'm not a techie when it comes to knowledge about horsepower, but I do believe epople want to mow faster. I used to mow my mother's yard with a 18hp Case tractor with a 60" deck-it took 2 hours going as fast as I could go with the power it had. I did it with a BX 2200, 60" deck, and it took me 1.5 hours-plenty of power, the limiting factor was comfort of the ride.

I now mow with a Toro 52" commercial ZTR with a 23 hp engine-I can do the same job in around an hour with a better cut-but if the grass gets ahead of me, I wish for 25 or 27 hp on that machine.

Will

 

[brokenot]

I could also get 19 mpg running over 75 miles per hour with that Torino

I've got to believe your fond memories of the car are causing you to remember things a little differently. How did you manage that kind of mileage back in the good ol' days of carburetion, no computer-optimized ignition timing (or any other instantaneously tweaked-on-the-fly parameters), a simple transmission without one, (or two) overdrive ranges, no locked-up torque converter, a third member gear ratio that *probably* had the engine singing at 3500 rpm or so at that road speed....etc. etc.

Just wondering out loud, 'cause I had several similar vehicles that would never approach that mileage number unless I was traveling downhill. And....while they were "fast" in their day, they would most certainly be soundly trounced by today's performance machinery.

 

[MessickFarmEqu]

one other factor here is that these over rated engines don't have torque like they used to. Older tractors could lug, new ones start to die under even a moderate load.

 

[LD1]

one other factor here is that these over rated engines don't have torque like they used to. Older tractors could lug, new ones start to die under even a moderate load.

That is mostly due to engine speed.

HP is simply a mathmatical calculation using RPM and torque. More of either results in more HP.

Old engines didnt tur many RPM's. But had a lot of torque.

New engines dont have a lot of torque but turn way more RPM's.

For example, the old ~25HP 8n's only ran ~2200RPM. A new kohler 25HP on a ZTR runs 3600RPM's. SAME HP, no two ways about it, but the 8n had more torque to get that RPM # at a much lower RPM, the new kohler uses RPM's to achieve the HP.

 

[tractorsanmore]

Years ago I owned a 1970 mach 1 351 cleveland 4v , 4 speed , dual exhaust , 300 hp. all stock and drove it to florida driving 65 or 70 mph . Was getting around 20 mpg . The car had close to 100,000 miles on it at the time .