cant beat rolling road time and a map that suits the car wrote for that car, where a generic map that was taken off a sort of like for like car a few year before and just just reused was always based on that first car as such and what that owner might of wanted from that map, ie low down torque or top end screaming etc, as for mapping a non force induction engine your restricted by the amount of air molecules within the induction stoke,, ie two much fuel will melt things so needs to be around 14.1 ration for best with a turbo you can increase the air so can add more fuel this gives a bigger burn off.