Busa ,man, "I know that its hard to change direction when the engine spins at 19.000 rpm... But i dont know why. " Well when the engine is spinning at such increidble speed,the tires do also.It will be a lot harder to do it..but that's F1-they have around 1500 kg of downforce :) I always gaze and gaze at the cars going absolutely flat out at the first massive change of direction at over 230km/h absolutely full throttle..then go through turn 7 and 8 at more than 200 on 5TH gear.. F1 never stops amazing me :)

"And another thing. When an engine can reach 21.000 rpm on a dyno... Why would it not be able to reach that value on the actual track?"
Well its an entirely different environment...first of all-running such high rpm in the factory with no risk is one thing-doing so in the most expensive sport in the world is totally different :)
Also the compression effect of the air in the air duct is enormous and extremely significant.I dont know if they simulate it on the dyno.And another thing-I dont know how F1 dynos work but on the track-the engine is "loaded" with the job of spinning,clutch,gearbox,all kinds of shafts and systems,differential,tires... :)
I am glad to have given you useful info bro .Take care :)