Nitrous drastically increases the efficiency of the motor, by creating a quicker and cleaner burn. The quicker and cleaner the burn, the less spark lead the motor needs. No different than a motor with poor heads needing 40* of timing to run hard and when you put a better head on it, then it only needs 32* to run hard. You have made the motor more efficient. Timing does NOT make power. Timing is only when you light the fire in the hole in an attempt to have a complete burn by about 15* ATDC. When you think about it, advanced timing is fighting what you are trying to do. The sooner you light it, the more the motor has to overcome in the increasing cylinder pressure of lighting the fire early. In a perfect world, the closer to TDC you could light the fire and burn it completely by 15 after, the more power you could make by freeing the motor up. Unfortunately engines are just not THAT efficient yet. I don't put timing in until it slows down and run the max I can. I pull timing OUT until it slows down. If it runs the same at 36* as it does at 40*, the latter is doing you no good and only increases your chances of pre-ignition.