You probably need a FPR. I doubt the stock ralliart regulator can handle a 255. I think they make a 190 which may be better suited for a RA. Or even a stock EVO pump.

 

First off, RA injectors are high impedance and EVO's are low will not work. RA f-pumps might have a regulator built-in that will allow up to a certain fuel pressure while EVO's or aftermarket need an external reg. If I where to install a walbro 255 with returnless probably the F-press will go up considerably and the pump in the long run will be damaged bc's the fuel doesnt flow back to the tank and its struggling to push back the excess fuel that's not squirted by the injectors. If the pressure is controlled by our ecu by means of variable voltage sent to the pump and not by an internal regulated pump then it might or could work.

2Cnts

 

When I added my 50 wet shot i was concerned about stock fuel pressure. the fuel pressure guage i added inline gives a steady reading of 55psi at idle. it's kinda hard to check the gauge under the hood when under load on the road. will check next time i hit the dyno tho