Does anyone know what pressure the std Classic Subaru OEM fuel pump's motor delivers its fuel (as if the FPR wasn't present)?

 

If the regulator wasn't there it wouldn't hardly have any pressure at all - it would just **** out everywhere. It's the regulator that controls the pressure, which is 3 bar as standard btw, with the vacuum line off. I think you probably mean how high could you take the fuel pressure with an adjustable regulator but still using the OE fuel pump? And I don't know the answer to that.

 

So. are you saying that the FPR causes the fuel to be pressurized at 3bar... when at idle i.e. c.650-750rpm?

 

Yes. Your idle sounds a little low, but basically yes, 3 bar fuel pressure is what your regulator does. This is controlled by the amount of vacuum it sees so with the vacuum hose disconnected you get (or should get) 3 bar, with it connected it drops to 2 and a bit. Of course you need a plumb a gauge into the fuel rails somewhere to read this off!