DIY: Cheap Big Injectors

Matt_Dean

Matt_Dean

Active Member
Premium Member
An easy and cheap way to get bigger injectors for running turbo/high comp/E85 etc. This will NOT make more power on its own, it is just a supporting mod for mods which require large amounts of fuel. This will require tuning to function correctly.
NASIOC Post: http://forums.nasioc.com/forums/showthread.php?s=&threadid=478921

Buy a set of 4 Subaru WRX 'blue' injectors, I paid $50 for mine. These are rated to 440cc but we are going to make them approximately 816cc


Grip the injector in a vice


Use a file to carefully file away the edges of the top, the top cap is only thin so you do not need to remove much material. Once enough material is removed simply peel the cap off the top.


That's it


This took me all of 5 minutes and cost me $50. This will require tuning and an adjustment of the injector scaling, hopefully someone with a bit more knowledge on this will chime in.
 
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It's commonly done and well documented in the Subaru scene and it's what Brendan is running now.
 
Matt_Dean said:
It's commonly done and well documented in the Subaru scene and it's what Brendan is running now.
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That's mad. Nice little automotive lifehack you've shared with us then :)
What kind of gains would you be expecting from a quick DIY like this?
 
Won't actually make any gains on its own but it's necessary for mods like turbo, E85 or high compression etc
 
As much as you guys are calling dodgy on this... this is actual legit thing to do
if you look at a large % of high flow injectors you will see they also have no "pattern" to speak of its just a hole.
the force of injection helps atomize the fuel in the high flows, although its not as nice as stock, but you cant make much power on stock injectors.

fig.1
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2SLO_4U said:
Can this be done on the stock injectors?
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not sure, but there is no point, as you would have to retune anyway otherwise you will just waste fuel and run rich on a stock tune.
also you can get yellows among other OEM injectors that suit 4g9x's with larger than stock flow for NA applications (still require tune)
 
every injector upgrade will require a retune or you'll end up running pig rich and loosing power. if you at this point where your decapping injectors you should really be looking at properly flow tested and matched sets.
 
If you arent running forced induction with E85 or an 250kw PULP setup you dont need to decap any wrx blue or sti pink injector, period.
Hope no one does this modification without proper tuning and monitoring of the air fuel mixtures.

Its a good hack and the injectors generally flow within a few % of each other. Still within a factory spec but obvious not always 1-2%
Spray pattern and atomization is fairly good.
Most people wont even have to decap them.
You will only need to decap on E85 since you require additional 30% fuel.

If you run STi pink 565cc, depending on power you plan with turbo conversion you wont need to decap to support E85.
Recapping the pinks yields about 960cc flow at 3bar fuel pressure
They use the same plug and are high impedance so it is perfect for you guys that dont have injector resistor ballast.
Id say Decapped sti pink would support around the 300kw at the wheels mark.
If you dont need to decap it then dont decap it because you will lose control and linearity at low injector pulsewidth.

One disadvantage in doing this is you do not any data on injector dead time, opening closing etc because the injector is now modified.
One needs to know what they are doing to dial them in so they run decent but then again even if you got data on it its not one size fits all on all ECUs.
 
I've updated the first post with a good read from NASIOC about the effects of this mod.
 
Ive seen the pinks flow 960cc on the bench but the blue flow 750cc?
I will have a injector flow bench next year.
 
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