Step 7: Check Fuel Quality & Ignition Timing
The last thing to do before enjoying your new nitrous system is to ensure that premium fuel (92 R/M Octane or
better) is in the fuel tank and that your ignition timing is programmed correctly. All recommended ignition
timing retard amounts, in the Tune-Up Specs, are calculated off of the base, stock ignition table. It is not
recommended to go above 75hp without an ECU reprogram, designed for nitrous. If the correct ignition timing
program is not used for the higher horsepower settings, severe engine damage may occur from detonation.
That is from the instructions on the 2005 Mustang kit.
I really don't like ZEX instructions but you get the point from this paragraph.