* Engine design: Two-stroke vs. four-stroke, single-cylinder vs. multi-cylinder, overhead cam vs. pushrod, etc., all significantly impact power output.
* Engine tuning: Carburetion/fuel injection settings, compression ratio, exhaust system design, and other tuning parameters dramatically affect horsepower.
* Engine condition: A well-maintained engine will produce more power than a poorly maintained one.
A 163cc engine might produce anywhere from 5 hp to 20 hp or even slightly more, depending on the factors listed above. You'd need to consult the engine's specifications (often found on a sticker on the engine itself or in the manufacturer's documentation) to find its rated horsepower.
