Why Capacity of Engine measures in CC?

CC is simply the volume displacement of the engine per rev.

HP is a different rating, of actual power produced by the engine. HP and CC are related (like distant cousins), but as far as I know, there is no reliable way to really relate the two, for they are measurements of entirely different things. HP can be increased, or decreased on the exact same CC displacement engine, with many factors.. (exhaust/intake/turbochargers/superchargers/chips/etc etc etc.)

CC is a measure of volume were hp is a measure of power. Where increasing the cc generally increases hp. There other things that can be done to and engine to increase hp with out effecting the displacement.

cc is being used to indicate engine size not power.

seems a convincing reply. Thx.

Two different measures.

Horsepower is power (force/distance relationship)

CC is engine displacement (size, volume, etc.)

I would guess engine sizes are rated in CC more often because an engine with a larger volume will use more fuel, produce more emissions, be physically bigger and normally drive a larger vehicle so it gives a more generalised description of what it will do. An engine with a high power output may not have to be particularly large, as mentioned above, you can fit devices to increase the power. Horsepower can be increased by engine tuning, more volatile fuel, supercharging or exhaust turbo boosting.

This site gives some answers:

http://www.simetric.co.uk/si_cc2hp.htm

To supplement the other fine answers above:

Nobody can dispute what a cc is. OTOH, nobody can agree on what hp is, or at least how to measure it. It would be marketing run wild, and if you don't believe me, pick up any aftermarket parts catalog (car, truck, bike) and look at the wild, largely unsubstantiated, or heavily asterisked claims for high performance parts.

The displacement of an engine in "cc" remains constant, even when the engine is stopped. The horsepower the engine delivers depends on the torque it produces at a given speed. Therefore the horsepower can only be specified under operating conditions.

Technically speaking (RAC or British Tax) HP was also a measure of engine size many years ago.

What you Guys are really talking about is BHP........which is a variable depending tuning, fuel type, engine size in CC etc etc.....

Here is a good definition of ALL the definitions!!

http://en.wikipedia.org/wiki/Horse_power

because for any given CC the horsepower would be different depending on the auxilary units to the engine......

your run of the mill 302 is not going to be a match for a race built 302.....

the HP curve is shown on the spec sheet , along with the torque, using RPM as the variable

CC= Cubic Centimeters Pie R squared * H

HP= Horse Power 33000Lb 1 foot 1 min

No direct relation

Yes, generally higher displacement indicates greater HP

Plus, in UK (don't know about other countries) CC is stated because it is som,ething that it stipulated by law about what size-engine vehicles may be used on the motorway (nothing at 50cc or under may use the motorway)...other than that I can only assume it is quoted because it is something consumers want to know? As is mentioned above HP is increased with larger displacement (but larger HP does not mean higher CC due to 'pimping out' your m/c) meaning the consumer can have a rough guesstimate as to what s/he can expect from the machine