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Originally Posted by sperry
Fuel flow is entirely determined by injector duty cycle and pressure at the rail. The amount of fuel flowing out of an injector is based on how long the injector is open, and how much pressure there is behind the injector.
I don't see how a larger pump on a stock car can change anything except how much fuel is cycled past the rails and back into the gas tank.
Apparently a stock STi that's tuned for more boost, and running its injectors at much higher rates to compensate, can run out of pressure in the rails. Since the stock mapping never runs the injectors at 100% DC, it's not a problem on a stock car. But if you're getting up there in DC, then you can run into the need for a bigger pump on an otherwise "stock" STi. i.e. the stock STi injectors are too big for the stock fuel pump if you tune it beyond stock power levels.
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That's what I was saying. Stock WRX injectors can't outrun the stock fuel pump, but stock STi injectors can. If you had an infinitely capable fuel pump, you could make your injectors "bigger" by cranking up the fuel pressure, which increases the volume of fuel sprayed for each millisecond it is open. That's limited in how true it is in practice though, because you run into issues with the fuel lines, spray patterns, poor atomization, etc. Plus the part where there is no such thing as an infinite fuel pump...
Also, the other factor in how much flow an injector is capable of is the size of the nozzle. The only difference between WRX "blues" and STi "pinks" is the size and number of holes in the injector nozzle. The plastic and the solenoid are the same.