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on the fuel distributer next to the return line is a bolt, that is the fuel pressure regulator inside you will find a spring and a plunger. and maybe some shims. you can ad shims to increase the fuel presure. the shims are the same in the b21 distributer. the part mubbers are 4627791 for large and 462792 for small. the small (.0039in) .1mm will raise the presure .8psi and the large (.0196in) .5mm will raise the presure 4.3psi. on how much you raise your fuel pressure depends on if it was rigth to begin with and how well your engine breaths(header? porting? larger valves? i think the closed box you speak of is you control pressure regulator. i'm not sure what you mean by a chokeable regulater. but you can replace the line presure regulator with a rising rate one. with a rrfpr you can tune it so the fuel presure stays stock when the car is at mid to low load and it will raise it at full vacume . so you can have more power with good gas milage and drivability. the are very expinsive. bell enginering group makes the best. well best of luck.