Taken from: Injector, Fuel Pump, and Fuel Rail FAQ: Read if you are thinking of upgrading! - NASIOC

Fuel Pump FAQ's:

What are the OEM fuel pump sizes?
2002-2005 WRX fuel pump 130 lph
2006-2007 WRX fuel pump 145 lph
2008-2009 WRX fuel pump 155 lph
2004-2007 STI fuel pump 145 lph
2008-2009 STI fuel pump 175 lph

What is the best fuel pump? The most commonly used fuel pump is the Walbro 342 fuel pump. It is a drop in unit that supports most aftermarket turbo fueling requirements. Other fuel pumps that are commonly used are:
a. Walbro 341 fuel pump. Functionally identical to the 342. Requires slight modification for use.
b. Supra Denso fuel pump. OEM quality fuel pump. Requires slight modification for use.
c. Buscher Racing fuel pump. Generally for high HP applications only though.
d. Perrin Performance fuel pump. Generally for high HP applications only though.
e. Aeromotive fuel pump. Generally for high HP applications only though.

What about the 08+ WRX/STI? There have been changes to the fuel pump on these models over to the Legacy style pump, so they are no longer "plug and play" swaps like previous models. P&L Motorsports offers pre-assembled Walbro pump units to swap out though as does Rallitek. There is a DIY option to do this as well and it can be found via this link.

Is there anything to look out for with fuel pumps? When using aftermarket fuel pumps, many re-use the stock WRX fuel pump filter. This filter contains a hard plastic skeleton inside to prevent the pump from ingesting the soft "bag filter". Aftermarket pumps do not have the hard plastic part, and many users enjoy the additional safety that the OEM filter provides over the aftermarket fuel pump's filter.

Do I need to tune for a fuel pump? No.

Can I run an aftermarket fuel pump by itself without new injectors/turbo/management? During the turbo upgrade path, it may be easier to purchase and install a fuel pump ahead of time. It is cheap, easy to install, and removes an eventuality from the upgrade chain ahead of time. You can run an aftermarket fuel pump with no other modifications. Adding a fuel pump will not give you more fuel (i.e. richen your car), it simply allows for more fuel to be delivered if you run higher boost or larger injectors. The stock RRFPR keeps the pressure at the stock 43 psi + manifold pressure no matter how much fuel may be available from the pump.

How hard is it to install a fuel pump? Allow around one hour for install time. Professional installation, depending on your area, is around $75. This is one vehicle modification that is very simple and can be successfully accomplished by even the greenest shade tree mechanic.

How do I install a fuel pump? Refer to the fuel pump manufacturer's instructions. For fuel pumps without instructions, below is are some links to some of the better known fuel pump installation instructions:

scoobymods.com instructions
scoobymods.com instructions
scoobymods.com instructions
TurboXS's instructions
Quantum Racing's instructions

Injector FAQ

What are the best fuel injectors? Fuelinjectors should be purchased based on the best possible match between the flow rating and needs of your aftermarket turbo. This should be a determination by your tuner to provide the best possible match. It is better to opt on the side of too large if there is any possibility of maxing out the injectors with your upgrade plans. Bigger is not always better with injectors so it is always best to purchase injectors best suited for your application and upgrade as need as opposed to starting off too large. This online calculator may assist you in the decision process. This post by hotrod will also help. As well, ask your tuner for his recommendation on brands. It will be cheaper to buy the brand he is familiar with rather than wasting dyno time + tuner fees while he fiddles around with your rogue brand injectors.

What type of injectors do I need? Aside from matching the injector flow for your turbo/tuning needs, you need to get the correct type for your vehicle:

WRX uses high impedance top feed injectors
04-06 STI uses high impedance side feed injectors (also called bottom feed)
07+ STI uses high impedance top feed injectors

What is the difference between low and high impedance? Low impedance injectors need to be electrically adapted to work properly, and usually come with the required electronic components for this.

Do I need to consult with my tuner about injectors? Yes. Items in your car that can be tuner specific: manual boost controllers, electronic boost controllers, upgraded wastegates, restrictor pills, wastegate helper springs, external wastegates (type/size/brand), and injector types/brands/sizes. ALWAYS take your tuner's advice on these matters no matter what the internet tells you!

Can I run a aftermarket injectors without tuning? No. You MUST have your car tuned during the installation process. Most tuners can send you a "limp map" based on your mods to tide you over during the break-in period or to get you to their shop for a tune days or weeks later. This map will be safe, but you should drive like your car is a 1990 Ford Escort until your final tune.

The map notes from XXX tuning company say pinks, but 06 injectors flow the same so can't I use them? No. Don't think you can out-think a tuner. If you have a question, ASK FIRST. And, as above, don't trust the internet, trust your tuner.

Are there any cautions with injectors? UTEC users should be aware that they should not use low impedance injectors. There is supposed to be a fix for this sometime soon (or may be out, can someone confirm?).

What are IDCs? The injector duty cycle is the proportion of time that the injector is open, squirting fuel. When choosing injectors, many try to choose an injector size to place IDCs in the 85-90% range. This assures proper fueling with a little bit of headroom.

(Dunno if I'm allowed to post this..i did look through the rules etc. Anyway the original link is: Injector, Fuel Pump, and Fuel Rail FAQ: Read if you are thinking of upgrading! - NASIOC - Just thought it would be very helpful for p.wrx members)

Good information to be found on the NASIOC FAQ's. But it is pretty general for USA spec stuff.

As noted many times in the FAQ, 'doing a mod, see your tuner first'.

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