Small Engine Horsepower vs CC

A reader writes…

Why don’t they give horsepower rating anymore? That’s all I’ve ever known. I can’t think in terms of displacement (CC’s). How do I know what’s going to get the job done?

Good question. So, let’s take a look at it.


HORSEPOWER

Horse Power! It brings to mind visions of Clydesdale’s; their flowing white manes thrashing in synchronicity, as they drive effortlessly across a snowy tundra, pulling a 6000 gallon keg on a iron reinforced buckboard and a man with a shotgun stares solemnly into the misty distance! YEEEEAAAH! Horses, man! Snow! Beer! HORSE POWER!

Way back in the early 1780’s, a Scottish inventor and engineer by the name of James Watt saw a great opportunity to sell steam powered engines to the brewers of London.

But in order to convince his potential customers that the steam engines would be able to produce enough power to meet their needs, Watt and his partner Matthew Boulton  came up with a clever way to clever way to connect the new fangled engines with the tried and true workmanship of the work horse.

Watt determined that the typical brewery horse, attached to a mill that ground the mash for making beer, walked at a relative speed of 180.96 feet per minute in a 24-foot diameter circle, pulling around 180 pounds of force.

Watt simply multiplied the speed times the force and came up with 32,580 ft-lbs per minute, which rounded up, comes to 33,000 ft-lbs/minute. And this…is what we refer to as one horsepower.

Wanna make math fun? Throw horse poop in the mix.

Eventually, the phrase became antiquated when considering actual engine capacity and became more of a catch phrase for salesmen.

I like horses, they have soft, fuzzy noses.


THE WHOSIWHAT?

So, for the longest time engine power ratings have been equated through the “horsepower” scale. But as engine technology has advanced, what was once as simple as finding the right diameter of coupling for your steam pipe is now a game of exact distances. Often measured in centimeters. Specifically “cubic centimeters” or “CC’s”.

The cubic centimeter represents the volume within a 1cm x 1cm x 1cm cube shaped space. In reference to the internal combustion engine, “cc” refers to the total volume of engine displacement. Engine displacement is determined from the bore and stroke of an engine’s cylinders. The bore is the diameter of the circular chambers cut into the cylinder block.


SO, WHY CHANGE?

The shortest answer is: Metrics.

Exact measurements make for a happy engine and a unified measurement system brings everybody on board for the big win. So, sometime during the late 20th century, the United States adopted something called the “International System of Units (SI)“, which allowed for a unilateral conversion from standard measurements in engines to metrics.

Once the car boys climbed on, the small engine guys were soon to follow and there you have it.

THE GREAT CONVERSION EXPERIENCE

I receive lots of emails asking me to find a blah blah horsepower engine, when the manufacturer no longer uses that measurement. And, yes there is an equation that will allow one to convert from CC to horsepower. It is an ancient, forbidden text, ancient known only to those in servitude to the dark one…and French Canadians.

For those of you with a mathematical bent, let me try to sum it up for you.

In terms of automobile specifications, 1 horsepower is roughly equivalent to 15 to 17 cubic centimeters.

For actual mechanical conversion requiring a more specific result, consider cc displacement (cubic centimeter size of engine) divided by 16 divided by 2 will get you in the right ball park.

So, there you have it. CC’s vs. Horsepower.

I suppose when you look at it that way, it all sort of measures up.

HA!

-Bill

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Bill Brown

Bill Brown

Bill is the head of content creation for the LawnMowerPros Blog and DIY section. He’s been in the Outdoor Power Equipment Industry for years and he’s still learning new things everyday. You can often find him creating featured articles, DIY guides, videos, graphics and much more.