What is the top speed of a Honda 8hp go kart engine?

It really depends on many factors. some factors include tire diameter, The gross weight of the car, the engine rpm, the way you gear it and whether you used a torque converter or clutch. There are too many factors that you have not included in your question for me to give you an answer. you can gear your engine for more speed and less torque, or you can gear it for more torque and less speed. Torque allows you to accelerate faster but you wont be able to reach a the same max speed as if you geared it for speed. if you solely want speed and you are on a flat paved surface, a clutch would allow more speed, but if you're planning on riding really any other area then you would want a torque converter or else you will blow your clutch.