How do I change top speed on A-Chassis?

I'm kind of a beginner scripter so I don't understand how to make the top speed. I've heard to change the horsepower but that makes it faster, and nothing in the engine tab helps in the A-Chassis script. Am I doing something wrong or is it that I need to change a different script. It would be perfect if there was a way to change the maximum speed via a value or in the A-Chassis script itself.