as you get to know your car, you will feel when you are past your engines horsepower peak, as the engine will "nose over", meaning it will feel like it is starting to lose power, because it is. at that point you want to pull the next gear. contrary to popular opinion, valve float does not always mean the valves are hitting the pistons. that depends on the rpm the engine is turning at the time. if you float the valves at say 5000 rpm, chances are the valves wont hit the pistons, but much beyond that they will.