Adjustable fuel pressure regulator allows manipulation to the stock fuel pressure. For the limited 370cc stock S13 SR20DET injectors, one can squeeze out more fuel by raising the fuel pressure a bit from stock 36psi base pressure. The regulator still retains the factory 1:1 boost dependent ratio. Another benefit for changing the old regulator is that the old stock fuel pressure regulator can be sticking and creates problems such as hard cold/hot starts and excessive rich/lean conditions. * Will also fit RB25DET.