determining size of small engine

[circus]

Been shopping for equipment with small engines. Nothing has horse power ratings any more. What"s up. Displacement tells me nothing. My 690cc lawnmower makes 18 hp while my 740cc motorcycle makes 80.

 

[NCWayne]

No HP ratings is the most stupid thing I have ever seen....The way I hear it, it basically turns out that different mfgs rated their engines differently and because of that the lawyers decided some, or all of them, were all guilty of false advertising. So, it's easier and less liablous for them to give no information and let you figure it out for yourself than it is for them to provide any help that someone could b!tch and file a lawsuit over........ Yes there's more to it all than just that, but from what I have seen and heard that's all a big part of it.......


Maybe we all need to find a way to sure for being sick and tired of all the stupid BS we have to put up with nowdays.........and get enough in the settlement that we buy our own island and never have to put up with stupid BS again.....Hey, a man can dream can't he...LOL

 

[36 Coupe]

GOV bureaurats put an RPM limit on lawn mower engines.My 6.5 hp mower engine cuts grass at about 3 hp level of old mowers.A true 5 hp engine would mow hay with out slowing down.The old 5hp with speed control was a better idea.Stoves with labels that say Caution .Hot when in use, dribbling gas cans are the result of gov regs.The last shot gun I bought is marked Caution misuse can cause injury or death.A truck with a 300 hp rated engine only uses 30 to 50 hp to go along the road.I am still trying to make sense of the lawn mower suit.

 

[brokenot]

Your motorcycle engine versus lawnmower engine comparison reveals such a large gap in horsepower-to-displacement mainly because your motorcycle engine isn't rated at a governed rpm. Small equipment engines are typically rated at 3600 rpm...for a couple of reasons.

The apparatus the engine is powering, (be it a set of whirling blades, a hydraulic pump, a blower fan, a generator head, etc. etc.), are designed to operate most efficiently while being driven at a given speed. Additionally, the engine needs to live comfortably and reliably for years while being subjected to whatever load they're operating. So unlike the motorcycle engine, the hp rating [i:f44c4ffebc]isn't[/i:f44c4ffebc] the peak number the engine can deliver, it's the hp at the [i:f44c4ffebc]governed[/i:f44c4ffebc] engine speed. (This is not to say you can disable the governor and get double the horsepower or anything, because the engines are designed to operate at or around that governed speed. Ignition timing, fuel delivery systems, camshaft profiles, valve area, port sizes, etc. are all kept in mind by the OEMs when that governed engine speed target is considered.)

Nowadays it is more difficult to ascertain what the mumbo-jumbo from the manufacturers means, but I attribute a lot of that to the average simple-minded consumer. If we see a *bigger* number on a specs card propped up next to a piece of equipment, (be it a mower/compressor/whatever), we'll gravitate towards that model. Real information be d@mned.

"Peak horsepower" and other such nonsense means little or nothing when it comes to engine-driven power equipment or equipment driven by electric motors. On one hand, I'm glad manufacturers were told to reel in their exaggeration a bit. On the other hand, I kind of miss the case of *induced giggles* I used to get as I saw people comparing things like "6 peak horsepower" shop vacs to one another at places like Sears.

(Not picking on Sears, mind you....just sayin')

:wink:

 

[TimV]

Wayne: leaving aside the issue with lawyers and lawsuits in general, the problem with misleading horsepower numbers on small engines and motors was an issue that HAD to be addressed. It"s hardly a new issue, as it"s been a problem in many other areas before and has needed to be addressed there as well. For instance, the Nebraska Tractor Tests of over half a century ago were started in large part because tractor manufacturers played similar games with their horsepower numbers, and over the years the same problem has been addressed with cars, outboard motors, jet engines, and pretty much every other form of mechanical power. The basic reason is that consumers (be they farmers, car buyers, or gardeners) need to have a common standard to compare products, and the "horsepower inflation" that had taken over the small engine and consumer electronics business had taken away that ability, forcing even normally reliable companies to artificially inflate their horsepower figures to appear competitive. Tests that offer a common denominator already exist, but now the challenge is to convince consumers that they can be believed, and that the same engine that was offered as "15 hp" can be sold to the same people as "8 hp". Until then, most manufacturers selling into the consumer market are just labeling their products with things like the cubic displacements, which are much easier to verify. If I had to guess, I"d bet that at some point in the future you"ll see HP ratings used again, but probably only if independently verified by some place like UL. It"s still not a foolproof system but at least it offers another level of objectivity. Even then, HP is not the be-all-end-all number of engine performance, particularly on engines (like many small engines) that are run at one speed, but at least it"s an easily recognized one, and one that needs to be based on a common set of measurements in order to be valid when used as a comparison between similar models offered by different manufacturers.

 

[Indiana Ken]

I believe the current engines all carry a torque rating...? To calculate the HP of the current lawn mower engines one has to assume a RPM value. As stated on another post most of these engines are designed to operate at 3600 RPM. Unless an actual operating RPM is given I use 3600. Note as long as the same RPM value is used any engine can be compared to another from the given torque value.

HP is calculated using the following equation; HP = [Torque (ft-lbs) times RPM (revolutions per minute)] divided by 5252. The 5252 is simply a constant to make the units work with ft-lbs and revolutions per minute.

For example: An engine rated at 8.75 ft-lbs torque will make 6HP ASUMING the 8.75 ft-lbs was measured at 3600 RPM. NOTE - since they do state the RPM value at which the torque is produced the calculated HP can only be used for comparsion to another engine.

The sad thing is the manufacturers HP ratings were problematic before since the test method was not stated and the torque ratings are also problematic since the RPM value is not stated.

 

[MPK]

I was told by a guy that sells mowers and snowblowers that you can get close by taking the CC and divide by 32 and that will give HP. Close but not exact.

 

[RN]

Horsepower ratings on small engines? The "best" most accurate rating is a DIN rating- meaning all operating equipment on engine and the horse power at shaft has a stated rpm figure that had normal governor. Problem for US was the SAE standards were for a peak rating with no muffler or aircleaner or "other" equipment used in automative industry was used by the small engine makers or the equipment maker- since they used the same accepted standards of "engine industry" it wasn"t illegal, just a little (maybe a lot?) misleading. Late 1970"s the car people were told to advertised "wheel" horsepower as car was normally equipped -dyno readings taken at rear drive wheels meant last years Chevy sedan with the 327 at 225 hp became a 160hp model. Nebraska tests had a drawbar power and a PTO or pulley power as normally equipped figure at noted rpm and all equipment on engine. How do you want to measure a riding lawnmower or a garden tractor- wheel, draw bar or mower blade shaft? Pump, sprayer or log splitter? A shaft torque rating at a stated rpm and a easily checked engine size avoid some legal hassles while giving a rough fair comparison. Note that the 3600 rpm figure for comparison may vary- some engines were designed to be used at about 2400 rpm for a earlier use standard, some at 1800 for a generator standard that would result in 60 cycle current, the 3200 rpm with a 6:1 reduction got a pto at about 540rpm that was old standard for pto equipment. Many of the engines under dispute had some ratings taken at 4000 rpm- the usable peak governed rpm for log splitters that would at times need a couple seconds of extra power and for the hydrostat units when cold start. Get displacement, check valve timeing and get compression, then use the very old SAE "taxable" power rating system and you"ll get as good a comparison as some of the advertising agencies-- and will be a good working figure for required power for work load. RN

 

[David G]

I did what Ken stated, but derate the torque a little at max RPM.

 

[Russ from MN]

I bet your motorcycle runs much higher rpm's and is possibly liquid cooled, that's what it takes to make horsepower, and horsepower generates heat! That's why most high performance engines are liquid cooled with aluminum heads or complete aluminum engines, with fuel injection and some turbocharged. Use lots of fuel, generate lots of heat, but produce lots of horsepower. We would nor want to pay for all that for a lawn mower!

 

[buickanddeere]

At best a well tuned two valve four stroke gasser may make 1HP per cu " at 6000rpm. So 1/2 HP per cu" at 3600rpm is a reasonable max for an engine as such.
Run of the mill two strokes make 100HP per 1000cc.
Of course any decent built bike or semi race engine will be 1-1/2 to double those HP numbers.