how much horsepower does a human have
The power a human can generate is highly dependent on the duration of the effort. In a four-second burst, a weightlifter might generate 3 horsepower. A world-class cyclist will generate 0.65 hp for a 1-hour time trial -- all-out effort. Most recreational cyclists generate about 0.35 hp for a sustained (2 hour) ride. Consider 1 hp to be the absolute maximum you can generate, and this chart will give you a rough idea of how fast you'll go, depending on your bike.