i set mine about halfway or a tic or 2 above. it works great and lasts all race use it in any gear above 3 and it will make a impact on ur lap times for sure. side note:
you can buy comp controled nitrous which is activated by aplication of full throtle in a real car it lasts a long time too and doesn't cause significant engine wear if set corectly by a trained technition i have it in my STI at home set for a 35hp increase at full throtle works great but generally used in drag style racing not touring championships