1 horse power is about how many watts your engine makes at peak output. The higher the horsepower, the more torque you have. A 1 hp engine is only capable of making a little bit of torque, so you're going to be very slow. If you were to use a 1-horsepower engine in a car, you'd be limited to speeds of about 20mph. It would also be impossible to run the headlights or the air conditioning. The low power engine would also affect acceleration. The bigger the engine, the faster it can go from 0 to 60 miles per hour. With the 1 HP engine it would take you forever to get going.