Snow blower power ratings FAQ

Your best bet is to find old literature for small engines and make a chart of displacement=hp. Then use that chart to determine approximate HP of newer equipment where you know the displacement but not the HP. It will be a fairly accurate guide.

Horsepower to CC is highly variable and not a good measure of power. My cars have different engines. The 3800 cc is 190 HP but my 3300 cc is 234 HP. I suspect smaller engines are similar.

Foot Pounds is actually more useful as it is the torque to the shaft that is doing the work. That said, none are truly meaningful in the whole scheme of things. What good is high horsepower ratings with a poorly designed snow throwing system?

Check out some models here

Unfortunately, not at all precisely, no...thanks to the dam lawyers :(

One can _VERY_CRUDELY_ estimate hp at about 60-70% of torque.

The relationship I recall (I'd have to go off and think again to re-derive the denominator) of hp ~ torque (ft-lb)*rpm/5250 which boils down to the above since most ratings are at 3200-3600 rpm.

Unfortunately, that's about best one can do other than simply try to find similar engine w/ known rating and compare based on displacement. Problem there is that tune and emissions requirements, etc., make that comparison as variable as the above.

Earlier Northern Tool catalog still listed an unofficial "old hp rating" as well but I just looked and the last one doesn't. Now I'm hoping I didn't throw the old one away and lose that cross-reference.

All in all, it sucks to guess how to compare even worse than before when ratings could be tweaked--at least you knew what Sears was doing w/ "peak" or "instantaneous" horsepower; the torque ratings might be absolutely accurate but they're still nearly useless as a comparison to previous ratings and certainly there's not even the same measure used if only provide displacement in one and torque in another.

For the types of engines generally found on lawn equipment, comparison of new engines and old engines of same brand and displacement is a valid comparison. These are utility engines designed to run at optimum RPM's while in use. A car engines is vastly different in it's requirements.

If an old snowthrower with a 13 hp Briggs engine is 350cc, then a new

B & S is using the foot pounds from what I've seen. an 8.5 ft lb is 6.5 hp

They are just trying to pull one over on us by frigging up standard ratings in the US. CC's equate more to Cubic Inches. Foot pounds equate to horsepower. Multiply horsepower by 33,000 to get foot pounds. It's just another crooked business tactic to screw you over.

See the chart:

Van Chocstraw wrote: ...

cc and ci are both displacements, yes.

torque and horsepower aren't the same units at all---

So a 3hp lawnmower has almost 100,000 ft-lb of torque??? Amazing! Them are some stout crankshafts...

Actually hp*33,000 --> ft-lbs/minute, _not_ ft-lb (as the table shows). The "per minute" part is significant here.

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Yes, "per minute" is the key. Same as how horsepower is measured.

"Horsepower is defined as work done over time. The exact definition of one horsepower is 33,000 lb.ft./minute. Put another way, if you were to lift 33,000 pounds one foot over a period of one minute, you would have been working at the rate of one horsepower. In this case, you'd have expended one horsepower-minute of energy."

Well, DOH! if 1-hp * 33,000 ft-lb/min/hp = 1 hp I guess it would follow that the definition of 1 hp 33,000 ft-lb/min...

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CC is cubic centimeters, CI is cubic inch, my new toro is 6.75 ft lbs of crap, it doesnt cut as well as an old 3.5 hp engine, the new ratings just decieve all. I thought my toro was 6.75 hp, I was ready to junk it because it bogs so bad.

Talk to a local shop that sells and services them, you wont get any service at the big stores

the HP is really irrelevant. Don't worry about it.

Not so! You neglected the time part of the conversion--it's (ft-lbs/Min). RPM is an input too all of this MLD

Foot lbs X rpm /5252 is horsepower. So you need to know the RPM.

The reason they have done this is because several companies were sued for over-rating the horsepower their engines actually put out. Like a lawn mower has a 4.5 HP engine (rated at 3600 rpm by the manufacturer) but because of the blade length and safety regulations the engine is limited to 2400 RPM on the mower (maximum velocity of discharge limit). So the 4.5HP engine is now 2.85 HP - but it is STILL a 6.56 ft lb engine.

Unless the old 350cc 13hp Briggs is a "side valve" engine with 5.6:1 compression ratio, and the new 350cc engine is an overhead valve engine with 11.5:1 compression ratio - which MIGHT be a 18HP engine.

Numbers just picked out of thin air, but the principal is there.

Multiply the old rating X 5252 and devide by 3600 and you have the torque rating of the old engine to compare. Virtually all of the old engines were rated at 3600 rpm.

My 140HP Corvair puts out 4,620,000 ft lbs of torque????????????????????????????

WOW!!!!!

It is the "old" 4.5 HP, but because of speed limits it is really only 3 hp - assuming 2400 RPM limit.

On a 24" mower, the blade tip travels 75.36 inches (6.28 ft) per revolution. At 3600 rpm that is 22,608 ft per minute - well in excess of the mandated 19,000 limit. The limit is reached at just 3025 RPM. So IF it is a 24" mower, it is a 3.88 HP mower.

I've never heard of two things mentioned here:

#1. a 24" push mower #2. a 2400 rpm limit

AFAIK, all small engines are governed at 3600 and that's where they operate.