Wondering about horsepower.

[99ls1ta]

The past few weeks I'd been looking at lawn tractors and it really got me thinking. Whats with all these huge hp power plants on small lawn tractors? I have limited knowledge on equipment but I know my grandfathers jd 214 only has 14hp my other grandfather has a cub series 2000 with a 12.5hp, dads Kubota 18hp all from the mid 90s early 00s. Now the smallest engine I found on the $1000 box store machines puts out 17.5hp why is that much required on small machines? Is there a different rating system in effect now? I know for a fact in the 70s there were tractors with only 8-10 hp running around doing a fine job, 25hp v-twin on a $1700 42in deck lawn tractor seems a bit overkill does it not? Or is 25 hp today = less back then (but then why are the jd x500s only around the 25hp mark)?

Also in the same subject I noticed there seems to be no hp ratings on the push mower engines anymore, They are now going on torque ratings (which makes more sense when you think about it) but one would think they could still give the hp rating as well (and give the torque rating for the tractors as well as hp). Just a few observations that got me wondering.

 

[PoorPlowboy]

Torque is the real measure of work and today's 24hp twin puts out about the same torque as an old iron 12hp.

 

[Baby Grand]

I don't know what happened, but I had the same experience. My mother in law's old, 12hp MHD didn't seem to be any weaker than our new, 2007 21hp Craftsman did. After many mechanical issues with that Craftsman we found an older 14hp Kubota G5200, which could mow circles around it. I think PoorPlowboy is right - it's torque that gets the job done. Torque over a wide range of engine speed is what makes the machine keep working, even when the revs drop under heavy load.

 

[MikeInEburg]

It's much like buying a pickup truck, once you decide to buy one, you'll start thinking "maybe I should go a bit bigger just in case". If 17HP is good, 20HP is better. It spirals up from there.

 

[oldballs]

Same wonderment here. Now some wise guy is displaying small engine sizes in "cc". Geeze...why not gives us all the numbers? and in French/Spanish/German/ Swahili too.:laughing:

 

[Gary Fowler]

Todays engines are just not as strong per HP as yesterdays. I had a 332 JD with 14 HP that pulled a 54" mower fine. I bought a used Troybuilt 17.5 HP that wouldn't pull a 42" mower in high grass even in 1st gear. I gave it to my daughter who still uses it to trim spots that her Kubota B2920 might miss with belly mower. I then bought a Craftsman with a B&S engine 26 HP and it cuts well, but it doesn't have any more power than my 23 HP Ferris with Kawasaki engine. I think it is all hype in the engine ratings now days.

 

[LD1]

Torque is the real measure of work and today's 24hp twin puts out about the same torque as an old iron 12hp.

If that were true, it would mean that todays engines have to spin twice the RPM to get double the HP number.

Either way, HP is just a number derived from the torque and RPM. So more HP either means more speed, or more torque.

HP is how fast work can get done. That is the important one. Not sure why small people say that small engines of yesterday feel more mowerful than ones of today? I dont have any experience with small consumer level mowers. But I had a JD 240 that was 12 or 14 HP. I now have a ZTR with 25HP kohler. And yea, it can cut grass about twice as fast. Which is spot on with having twice the HP.

And I dont mean its faster just because its more maneuverable. It will pull its 61" deck through thick grass much faster than the 240 would with a 46" deck without bogging.

 

[prosperity]

It's all about marketing. To the average consumer bigger is better, right?

Joe homeowner is looking at box store lawn tractors. Model 'A' is 18hp 50" cut for $3000.00. Model 'B' is 20hp 50" cut for $3500.00. Bigger has to be better so Joe buys the $3500.00 model It probably costs the manufacturer $40 more for the bigger engine so that means $460 more profit.

 

[zzvyb6]

My old '70s Craftsman magnesium case push mower had a big block 454 Chevy in it. Used about a gallon of fuel per month. Once it went to full throttle and hovercrafted itself into the side of the garage.

I think the motors and emission rules of today require the extra size rating, or maybe the hp ratings are actually accurate now.

 

[99ls1ta]

So I am correct in my thinking that the 25hp box store twins are still less "powerful" (torque/able to get work done) than the 22-24hp twins in the X5 deeres for example? Not talking anything tractor or quality related just power output engine to engine. Sort of like a Honda civic si engine vs a late 90s 350 v8 both make just north of 200hp but the v8 can work twice as hard.

I wish it was a little more like truck buying, here is the hp, torque, displacement, payload/towing cap etc right in the spec sheets. I know they are not all accurate but at least we have a ballpark on what we are getting unlike the power equipment world. If my above thinking is correct that hp number is so misleading since the torque is what is most important and dispite the same or higher hp rating its a weaker engine (again not quality just power output).

 

[LD1]

So I am correct in my thinking that the 25hp box store twins are still less "powerful" (torque/able to get work done) than the 22-24hp twins in the X5 deeres for example?

I dont think so. Just a quick peak at some specs,

The JD 24HP in their x500 series is 726cc
A 25 HP briggs v-twin pro found on a troybuilt is 724cc

I'd say they are on par.

HP is just a number that defines how much work can be done. If HP is the same, work that can be accomplished in a given time frame is the same.

Even with your civic and truck example. Fundamentally, HP is define as 33,000ft-lbs per minute. (in otherwords, its a number that defines how FAST torque can be applied).

So the 33000ft-lbs per minute could mean the power required to lift 33000 lbs, 1ft, in 1 minute.

OR it could bean 3300 lbs, 10ft, in 1 minute

Or 330lbs, 100ft, in 1 minute.

All require the same power to accomplish. Defined as 1HP.

So by definition, the civic and the truck @ 200hp, would be able to do the same work. But gearing comes into play though. While the civic might not be able to do 3300lbs 10ft with each of its HP, it might be able to do 330lbs at a rate 10x's faster.

The other thing to keep in mine is that those are peak HP ratings. The civic likely gets its rating @ 6000rpm or so. And the truck is likely down around 3800 rpm for its peak rating. So in real world driving ranging from 1500-3000rpm, the truck is making more HP (and yes, more torque). But wind the civic out to its peak power, and YES, it is capable of doing the same amount of work in the same time as the truck.

 

[Buggs67]

This makes me question why tractors are not advertised/sold with Torque ratings like 80 ftlbs at 2600 rpm. They are all rated by hp. And as I understand it, diesel engines make better torque per hp than gas engines. SO I'd like to know how much torque my Kioti makes at what RPM? I may have to contact the Mfg to ask.

 

[LD1]

This makes me question why tractors are not advertised/sold with Torque ratings like 80 ftlbs at 2600 rpm.

Because torque doesnt give any indication of how much work can get done in a given time frame. And if they give you "xx torque @ xxxx rpm" that is basically HP. Since HP is simply a calculation of torque and RPM.

diesel engines make better torque per hp than gas engines.

Incorrect. HP is a calculation using torque and RPM. HP dont care weather it comes from diesel or gas.

Now in modern things like trucks, gassers spin a higher RPM than diesels. Therefore, their HP rating is at a lot lower RPM. Meaning they have to have more torque to get an equal HP number since they cannot turn as many RPM's. IF you increase RPM's, HP will go up. If you can increase torque, HP will go up. So in a nutshell, gassers increase the RPM, diesels increase the torque, to result in equal HP numbers.

But since we are talking tractors, and no one seems to make gassers anymore, if you are talking about gassers of 4 or 5 decades ago, their peak RPM's were only 2000-2500, like the diesels. So with RPM's being the same, if the HP is the same, the torque is going to be nearly the same as well.

SO I'd like to know how much torque my Kioti makes at what RPM? I may have to contact the Mfg to ask.

With 24.5HP @ 2600 RPM, you are making ~50ft-lbs of torque at that speed. And will likely have a higher peak torque down around 1500rpm. But at less HP. Maybe something around 70ft-lbs.

But let me ask, what does knowing the engine torque gain you?? Why do you feel it important to know?

 

[99ls1ta]

So hp is a byproduct of torque right? the civic and pickup are producing the same amount of output just at a different rpm. I am learning so much from this site I messed around with cars most of my life, its weird to learn the 350 in a 98 suburban can only match a civic si in work output. you wouldn't happen to know the torque, rpm, hp equation would you?

If I am reading this correctly, since most everything in around the house lawn care is set to run at 3600 rpms a 24hp kohler courage in a mtd will have the same abilities as the 24hp Kawasaki in a jd x series (again just engine output not tractor cap. or durability). And they would both match a 24hp kubota diesel.

I still agree with you bugs seems like they should give the torque ratings as well it would just make buying easier when you are more informed, and most are like me was not aware of any of this till a few mins ago.

But once again still begs my original question why did we go from 10-18 being the norm for lawn tractors to 17.5-26 being standard. if a 18hp runs a Kubota with a 50in deck plenty quick why do we need 24 to do it now? I guess just marketing and bragging rights from what I'm reading.

 

[LD1]

So hp is a byproduct of torque right?

I guess you could say that

the civic and pickup are producing the same amount of output just at a different rpm.

Correct. Their "peak" ability is the same. But since the civics "peak" is ~6000rpm, and the 350 "peak" would be ~4000rpm, the peak of the 350 is closer to where it will actually be used in day-to-day driving. And at 1500-2000 rpm, the 350 is going to have more HP than the civic. Which is why it would seem to have more power.

you wouldn't happen to know the torque, rpm, hp equation would you?

HP= (tq x RPM)/5252 and (HP x 5252)/RPM = TQ

If I am reading this correctly, since most everything in around the house lawn care is set to run at 3600 rpms a 24hp kohler courage in a mtd will have the same abilities as the 24hp Kawasaki in a jd x series (again just engine output not tractor cap. or durability). And they would both match a 24hp kubota diesel.

Thats correct. Unless someone is lying about the numbers.

I still agree with you bugs seems like they should give the torque ratings as well it would just make buying easier when you are more informed, and most are like me was not aware of any of this till a few mins ago.

Sure, I'll admit it would be nice to see the torque specs. or even better a full torque/hp curve. But in reality, the torque isnt a measure of how much work it can get done in a given time. And 90% of the specs of a tractor or mower, I'll bet people dont even care about anyway. But HP is the more important number. It ticks me off that alot of the small engine MFG's quit listing it cause of the lawsuit they got burnt on.

But once again still begs my original question why did we go from 10-18 being the norm for lawn tractors to 17.5-26 being standard. if a 18hp runs a Kubota with a 50in deck plenty quick why do we need 24 to do it now? I guess just marketing and bragging rights from what I'm reading.

Alot of it is marketing and bragging rights. And in most cases, for a lawn tractor, 12 or 14 HP is pleanty for the average lawn. It will cut the grass just fine at a speed most mow at to be a comfortable ride, and be able to maneuver. More HP is better for not bogging down as bad if you let the mowing get behind. Or...provided they have sized the pulleys to allow for faster blade speed, more HP will allow you to cut at a faster ground speed.

Keep in mind, Horsepower isnt something that can actually be measured. IT is simply an equation formed to depict how fast torque can be applied. Torque is what is actually being measured. That in combination with RPM in the formula give the time aspect. Two engines may have equal power (like your suburban and civic example), but one may have higher torque. People like to reference "down low torque" or "more torque at lower rpm", which is correct. But More torque at lower RPM also means more HP at them lower RPM. If you could see a HP curve, it would be better than comparing peak HP. Cause then you can look at which engine has the most HP in the RPM in which you will use it the most, rather than what its peak is. In the case of 3600rpm small engines, they are almost always ran at 3600rpm. So knowing what the HP or torque is @ 1000rpm isnt really important IMO

 

[oldballs]

I think I can actually hear the difference when my neighbor mow his lawn with a big box riding mower. At a distance it probably is about 10-14 HP and screams like a banshee as he goes around. He's probably mowing at that 3,600 rpm, I guess. Whereas my Kubota B2620(26HP) mows at about 2,400 rpm and is not nearly as "loud". ...says I.

 

[CobyRupert]

Another question would be: Are the way they rate/label/test the engines today the same as it was before?
Example is that engine labeled 24hp really 24 hp with the stock carb, intake, exhaust and measured at a rpm that the motor you buy is capable of turning at? (i.e read the fine print.)
It's easy to get a motor making 20 hp motor up to 25 hp; just turn the throttle up from 2000 rpms to 2500

 

[LD1]

Another question would be: Are the way they rate/label/test the engines today the same as it was before?
Example is that engine labeled 24hp really 24 hp with the stock carb, intake, exhaust and measured at a rpm that the motor you buy is capable of turning at? (i.e read the fine print.)
It's easy to get a motor making 20 hp motor up to 25 hp; just turn the throttle up from 2000 rpms to 2500

I dont know how they test them. And dont know how they did test them. And also not sure why people believe the older engines are just as strong as ones with double the power today.

My old JD240 was 14hp. And it mowed well. had a kawasaki 420cc engine. Mowers today claiming 24 or 28 HP are running ~720cc v-twin engines. So regardless of what anyone things, I am inclined to believe a modern engine with ~70% more displacement does indeed have 70% more power.

Now how well a mower cuts is a different story. Lot of it has to do with blade speed and deck design. Which cannot be overcome with power.

 

[DeereMann]

Doesn't anybody remember the class action lawsuit against all small engine makers a number of years ago? They all were sued for ever-inflating power ratings that weren't even close to what they actually made.

That is the reason why many of them stopped that & went to gross torque output. Gross meaning the maximum the engine can make without any parasitics (air filters, etc.).

I received an unsolicited small amount of money from that lawsuit is how I remember it.

 

[LD1]

Doesn't anybody remember the class action lawsuit against all small engine makers a number of years ago? They all were sued for ever-inflating power ratings that weren't even close to what they actually made.

That is the reason why many of them stopped that & went to gross torque output. Gross meaning the maximum the engine can make without any parasitics (air filters, etc.).

I received an unsolicited small amount of money from that lawsuit is how I remember it.

Since HP cannot actually be measured, rather it is derived from torque and RPM, either they messed up the math, or overstated/measured the torque as well.

Either way, as with about 99% of advertising, lots of things are overrated, or overstated. This was just an easy get-rich-quick scheme that made the lawyers tons of money, and will be costing us (the consumers) for decades.

I know they are now rating the peak torque (usually at a lower RPM than what is normally operated. So what good is that? Peak torque is likely around 1500-1800rpm or so. If my mower, logsplitter, powerwasher, snowblower, etc is never ran at that RPM, what good is knowing what the torque is at that RPM.

I do wish they would at least give the torque @ operating RPM. Cause at least that way you can figure the HP.

But even worse, I see some small engines not even rated. Rather just a CC listed. Which does me no good at all when trying to size a motor.