I understand what you are asking. You dont want to have to be adjusting the timing all the time from running N/A to nitrous right? You will lose power by retarding it N/A. I had a bbc and I had it timed a 36 and bumped it up to 42 and the car picked up nearly a tenth so it will definatley slow down. If you sont want to have to manually reset the timing when you want to use nitrous I would suggest buying a retard module and then you can just change the chips and dont have to mess with the distributor.