Mexican Mopar 360: i need to know how to have more horsepowers

Hi my friends, sorry for my bad english. The last month, i buy a mexican valiant super bee with 300 hp. In mexico city, we are to 2400 meters above sea level, and the car does not reach more than 180 km per hour. I'm interested that changes you may make to the car to exceed 200 km per hour, about the height takes away power. If you can help me, i can appreciate that.
Regards