2. Another determining factor in the air/fuel ratio of the engine is the flowing fuel pressure of the nitrous system. This flow tool from Nitrous Supply and special jet fitting allows us to check the fuel pressure coming out of our regulator when the fuel pump is turned on. By plumbing this gauge into the outputs of the regulator and returning the fuel to the tank, we can turn on the pump and see exactly how much pressure the solenoids are seeing before the system is activated. Of course, there are always variables involved, such as voltage supply fluctuations when the solenoids are activated, but this is a pretty reliable method for establishing the fuel pressure of the system. We set our baseline fuel pressure at 6 psi and tuned from there.