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Old Dec 01, 2011, 04:49 PM
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Help me understand gas engines and cc rating

I do not understand what a cc means, regarding gas engines. Could someone explain this to me.

For example, how come a 49cc engine on a moped is physically so much larger than my 62cc aircraft engine?

How does CC relate to horsepower?
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Old Dec 01, 2011, 05:10 PM
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Quote:
Originally Posted by bsbauman View Post
I do not understand what a cc means, regarding gas engines. Could someone explain this to me.

For example, how come a 49cc engine on a moped is physically so much larger than my 62cc aircraft engine?

How does CC relate to horsepower?
Cubic Centimeter, the volume of space in the compression chamber. Where the piston is inside the cylinder.

Mopeds have geared transmissions which take up space, larger cooling fins and thicker walls on the cylinder. Also if it four stroke (oil seperated from gas or fuel) there is added room for oil routing and also room for valves and rods. Two stroke (gas and oil mixed together) is generally smaller.


Horsepower is not constant with CC, but varies dependent on fuel, delivery method, compression, exhaust and lots of other variables such as piston shape, head shape, etc.

That's just a brief answer, lots more to it. Plus RC engines are made to be compact and lightweight which is not a concern with something where a bit more weight is not an issue. Google "How Stuff Works"!
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Old Dec 01, 2011, 06:10 PM
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Also, our model aircraft engines have a big ole fan out front.
That's something you don't have on the moped, and it has to keep from overheating, even when sitting still.
So, lots of the physical outside size is in the huge fins on the head and cylinder, to carry the heat away.

Knock off the transmission, and trim the cooling fins to about the size we use, and it doesn't look so big by comparison any more

Take our airplane engines, trim off all/most of the fins, fit a water cooling jacket to make a marine motor, and they look even smaller.
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Old Dec 01, 2011, 06:58 PM
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stroke and bore size are also big factors in power/torque output with a little effect on packaging dimensions
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Old Dec 01, 2011, 07:04 PM
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Thanks guys Great responses; much more easily understood
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Old Dec 02, 2011, 01:13 AM
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Also think about weight difference. Models need to be light so the gas engines are built strong, but light. Mopeds don't really have to worry about that as much so they are built bigger and of different materials. I enjoy that fact that my G-62 is bigger than a moped and can fly.
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Old Dec 02, 2011, 07:23 AM
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I have backpack leafblowers with 50cc and 34cc engines. They're also pretty light.

Horsepower is a function of engine type (four stroke vs two stroke) but also design and state of tune. Engines designed to run at low power for long periods of time are very different to those required to provide a lot of power but in short bursts..
..a
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