I am looking for a new snow blower and have discovered that the power rating
of the engines are no longer in "Horse Power" but in "Foot Pounds" if given
at all. Sometimes all that is given is the CC's of the engine.
Even the people selling these machines don't know what the "Horse Power"
ratings are so that old geezers like myself can understand what is going on.
Does anyone have any general rules regarding the conversion of Foot Pounds
or CC's to Horse Power?
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
Check out some models here
If I was buying a new machine, I'd base my decision on features, size, drive
type, and what is important for my situation. The manufacturer will couple
the right sized engine to perform with the design of his machine. A half HP
difference is going to be not noticed, but a clogged chute will piss you off
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.
On Sat, 10 Oct 2009 11:01:54 -0400, "Ed Pawlowski"
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
If an old snowthrower with a 13 hp Briggs engine is 350cc, then a new
350cc Briggs powered snow blower will be about the same 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:
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.
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."
On Oct 10, 10:57=A0am, Van Chocstraw
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.
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.
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.