Go to ZEX's website, and last time I installed it it was 4.3Volts, stock on my sr20de was 4.03Volts at WOT, nothing was really different in the car, maybe a little more fuel consumption, I only used the N2O at the track anyways. But I am 100% it is 4.2Volts, I just put it at 4.3V to be safe. JCC