Then the piston must have a tight fit....
2 years ago it was hot for a short time. Sirio, GRP/Ninja, RB, OS and some more had these magnesium heads, where are they today? Many users mentioned higher temperatures and tunings issues as I have seen it within our nationals.
All manufacturers are drilling out aluminium heads to save weight and still have enough cooling.
Speed is only fiction but a 130+km/h MRS4 is for real.