First off, I am a noob to the Grand Prix GTP. Just got mine a week ago, but have been pining for one for years. Anyway, I am changing over to synthetic Royal Purple XPR (I am not trying to open the synthetic VS dino conversation again). Now from what I have read and discussed with others, an engine needs zinc and phosporus to help protect the metal on metal areas, IE cylinder walls, flat tappet cam, etc. What I planned on doing during the oil change was adding 4 liters of XPR and the remainder in RP Break In Oil because of its high zinc and phosphorus content.
My questions is this; Can you put too much zinc and/or phosphorus into an engine?
Second, the engine has been rebuilt and has all new seals. I have heard both, "Flush the engine" prior to switching to synthetic and, "It isn't necessary". What is the recommendation of the experts?
Thanks
