originally nissan said that the S12 can only run on leaded 4 star, ive had my S12 now for 8 years, always run it on unleaded. it wont damage the engine as the valve seats have the inserts same as used in unleaded heads, the only other thing that can cause a prob is the timing, some say you need to reatrd it slightly. i think 2 degrees was the amount, but unsure on this.
most people use tesco 99ron super
