Fuel Injectors and Fuel Pump
The factory injectors and fuel pump probably won't be able to deliver once you bolt on the bigger turbo, so you'll want to install some larger ones. Recent-model Subaru cars come with 565cc units. We usually upgrade to 1050cc units for most street cars, although larger fuel injectors may be appropriate depending on your upgrade plans. E85 (85% ethanol) fuel use requires much larger injectors -- as much as 70% larger than you would otherwise use for gasoline.
In most cases the fuel pump should also be upgraded. The 2002-2007 WRX fuel pump has to be replaced with any turbo upgrade. The 2008+ STI pump can supply enough fuel for mild turbo upgrades (up to 20G size on pump gas), but should be upgraded beyond that. When in doubt, upgrade.
Injector Dynamics is our preferred fuel injector supplier, and their complete selection of
Subaru-fit injectors offers drop-in replacements for just about any of the cars we serve. Our current favorite fuel pump is the
AEM 340 lph unit, which provides higher flow AND E85 compatibility.
Note that the 2015+ WRX uses direct fuel injection, which uses a mechanically-driven fuel pump and extremely high fuel pressures. The stock fuel system can handle substantially more horsepower than a port-injected car; we have seen over 400 whp on the stock high-pressure pump and injectors, and over 500 whp using E85 fuel. Note that the LOW-pressure fuel pump in the fuel tank still does have to be upgraded when a larger turbocharger is installed.
Next up:
Front-mounted intercooler
The factory injectors and fuel pump probably won't be able to deliver once you bolt on the bigger turbo, so you'll want to install some larger ones. Recent-model Subaru cars come with 565cc units. We usually upgrade to 1050cc units for most street cars, although larger fuel injectors may be appropriate depending on your upgrade plans. E85 (85% ethanol) fuel use requires much larger injectors -- as much as 70% larger than you would otherwise use for gasoline.