Injector, Fuel Pump, and Fuel Rail FAQ

Fuel Pump FAQ

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

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.

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? Fuel injectors 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.

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.

Is there a list of top feed injector sizes for the 2002-2007 WRX?

OEM 2002-2005 WRX 420 cc
Power Enterprise 510 cc
JDM STi “pinks” 550 cc
OEM 2006+ WRX 560 cc
DeatschWerks 565 cc
Modified OEM WRX 600 cc
Ultimate Racing 600 cc
Power Enterprise 650 cc
DeatschWerks 650 cc
Helix 660 cc
Ultimate Racing 680 cc
DeatschWerks 750 cc
Ultimate Racing 785 cc
Power Enterprise 800 cc
SARD 800 cc
Helix 820 cc
Modified Stock WRX 850 cc
DeatschWerks 850 cc
Ultimate Racing 900 cc
Ultimate Racing 1000 cc
DeatschWerks 1100 cc
Ultimate Racing 1260 cc
Ultimate Racing 1600 cc

Is there a list of injector sizes for the 2008 WRX?

No one knows size or top/side feed yet. Odds are they are 560 cc top feeds, but that’s just an educated guess.

Is there a list of side feed injector sizes for the 2004-2006 STI?

OEM 2004-2006 STi 535 cc
DeatschWerks 650 cc
DeatschWerks 740 cc
Ultimate Racing 785 cc*
Perrin 817 cc (modified stock injectors)
Agency Power 817 cc (modified stock injectors)
Power Enterprise 850 cc
DeatschWerks 850 cc
Helix 860 cc
Ultimate Racing 900 cc*
Ultimate Racing 1000 cc*
Ultimate Racing 1260 cc*
Ultimate Racing 1600 cc*

*Ultimate Racing STI injectors are top feed injectors with a rail conversion kit to allow them to work as side feeds. They are also low impedance and come with a resistor pack kit to allow them to work as high impedance.

Is there a list of top feed injector sizes for the 2007+ STI?

OEM 2007 STi 535 cc (guess, data unknown)
For the rest, refer to the above WRX chart

Who manufactures injectors?

Agency Power
DeatschWerks
Helix
Perrin Performance
Power Enterprise (low and high impedance versions)
RC Engineering (low and high impedance versions)
SARD
Ultimate Racing (low and high impedance versions)

Can I modify stock 02-05 WRX injectors for increased flow? Yes, though this route requires additional research, thought, time, and care than purchasing larger injectors.

600 cc injectors
740 cc injectors (Though this is the thread title and commonly known name, these modified injectors actually flow 850 cc when tested at the normal static fuel pressure of 43psi)

Can I modify stock 06+ WRX injectors or STi pinks for increased flow? Yes, but that would be a dumb move. These babies go for like $300 used. Sell them, buy 02-05 WRX injectors for like $150 and have them modded.

Are there any other mods to increase flow?
Yes, you can modify your stock FPR when using an aftermarket fuel pump to increase the cc rate of your existing injectors. View this thread or this thread for details.

How hard is it to install fuel injectors? Allow around two hours for install time. Professional installation, depending on your area, is around $150. This vehicle modification more difficult and time consuming than most “bolt on” installations.

How do I install fuel injectors? Refer to the fuel injector manufacturer’s instructions. For fuel injectors without instructions, below is a link to one of the better known fuel injector installation instructions:

TurboXS’s instructions
Useful NASIOC thread

Fuel Rail FAQ

What are fuel rails? Aftermarket fuel rails are designed to increase the internal diameter of the stock fuel lines as well as convert the OEM fuel rail set up from series to parallel. The theory behind these two changes is to increase fuel flow and equalize fuel distribution.

When are fuel rails needed? This is a very hard question without a clear answer. Two very reputable tuners and NASIOC Vendors do not believe they are necessary. god of Godspeed Inc. and nmyeti of TurboXS recently posted that they are not needed for additional fueling or fuel distribution equalization, which is the rumored cause of particular cylinder number failures. Another view by nmyeti. That being said, there is no real downside to fuel rails for people who believe they may provide an extra level of protection.

Who manufactures fuel rails?

APS
Aeromotive
Agency Power
BDL Industries
Crawford Performance
Outback Motorsports
Perrin Performance
Rocket Rally Rails
Subydude
TurboXS
Ultimate Racing
Vishnu
Boomba Racing

Is there a “fuel rail mod”? Yes. Many have modified their stock (series) fuel rails into parallel fuel rails.

scoobymods.com instructions
supporting/supplemental NASIOC thread
supporting/supplemental NASIOC thread

Are their other fuel rail mods? Yes. As detailed in this thread, Ultimate Racing offers fuel injectors that mimic fuel rails by being flow matched for each individual cylinder. These injectors are specifically matched so that each cylinder flows the exact amount of cc’s using the stock fuel rails. They also have flow matched units for parallel or aftermarket rails as well.

How hard is it to install fuel rails? Allow around six hours for install time. Professional installation, depending on your area, is around $400. This vehicle modification is more difficult and time consuming than most “bolt on” installations.

How do I install fuel rails? Refer to the fuel rail manufacturer’s instructions. For fuel rails without instructions, below are some links to installation instructions:

Perrin’s instructions
APS’s instructions
Vishnu’s instructions
Mike Egan’s instructions
Jorge’s instructions

Editors Note

This post was created because I wasn’t able to find a good FAQ on these parts. I came up with the text based on LOTS of searching here. Upon reading this you should have an idea of what type of fuel supporting modifications best suit your needs. The types and manufacturers are up to you.

If you find an error in this FAQ, please PM me with factual details and I will update this post. Responses such as, “I have XXX’s injectors and they are great!” or “XXX’s fuel rails cracked after 1 month” are not appreciated here, that is what the Car Parts Review Forum is for.

Leave a Reply

You can use these XHTML tags: <a href="" title=""> <abbr title=""> <acronym title=""> <blockquote cite=""> <code> <em> <strong>