The two inlet ports can be used for single or dual rails, and the two gauge ports allow the use, of both a mechanical gauge and electronic pressure sensor. What sets this product apart from the competitionWell, if you're looking for an EFIFuel Pressure Regulator that seals and behaves just like your factory unit butwith the added reliability and high flowing capacity you require, then look nofurther than the FX - D. How have we achieved this Our engineers have spent countless hours developing a unique replaceable co - polymer valve seat. What does this meanConventional aftermarket performance Fuel Pressure Regulators typically utilize a metal - to - metal valve and seat which by nature will not positively hold pressure when your engine is shut down, which can make startup more difficult. Here at Go Fast Bits, we have incorporated a softer, more compliant yet resilient material for the valve seat, which will always positively seal and hold fuel pressure on shut down, designed to give factory - like sealing and reliable startup, as well as superior fuel resistance suitable for Unleaded, Ethanol, Methanol, and Diesel fuels. We also use a double layer diaphragm, which means we have twice the reinforcing material, and as a result the burst strength exceeds 1000psi, The FX - R also offers multiple fuel inlet and gauge ports that allow for a wide range of fuel system setups beyond the usual inletoutlet, including parallel fuel rail or returnless deadhead systems. The two gauge ports allow you to run a mechanical fuel pressure gauge AND an ECU fuel, pressure sensor if you want to.