* Engine design: A high-performance, racing-tuned 139cc engine will produce significantly more horsepower than a basic, mass-produced engine of the same displacement.
* Type of engine: Two-stroke engines generally produce more power per cubic centimeter than four-stroke engines.
* Carburation/Fuel Injection: The efficiency of the fuel delivery system impacts horsepower.
* Tuning and modifications: Aftermarket parts and modifications can greatly increase or decrease horsepower.
Therefore, you could see anywhere from roughly 4 to 20 horsepower in a 139cc engine, depending on the factors mentioned above. A typical consumer-grade 139cc engine (like in a go-kart or small motorcycle) might be closer to the lower end of that range.
