I am new to nitrous and need to know should I tune my PCM for a 13.0 AFR N/A and when I tune for the spray am I only tuning the fuel jets to achieve the 12.0 to 12.5 AFR when on the bottle. I have a mallory 667 so timing will be pulled when the engine takes the hit.

 

Tune the PCM for optimum performance WITHOUT the nitrous. There is no "fixed" value of A/F ratio that produces the best performance. You have to try various combinations of A/F ratio and ignition timing.

Once you get the straight motor tune optimized, tune for nitrous with the fuel jet (assuming it's a wet system) and the timing retard. Again, no single value of A/F ratio works for every engine. It's going to be highly dependent on the size of the shot. Again, experiment, but always work from the rich side to avoid detonation. Read all the plugs to determine if you are getting to the point where you are going to see detonation.