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5th injector with G2


Dion Parker
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I would assume that if the RA had a fifth injector, it would of been used on motorsport models???  It is definitiely not as simple as just wiring it to an injector output.  Why do you want to run the extra injector?  Are you above 80% duty cycle at full power on the main injectors?  Do you have adequate fuel delivery (have you measured it)?  Running an extra injector will reduce your power output if air/fuel ratios are already correct...  Best option is to increase the main injector size if you need additional fuel...

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About the RA, I heard that in many cases it was not hooked up apart from on motorsport models. I am only running grey top injectors and these are maxxed out. My car runs a few mods and the injectors are over 80%. My plan was to run some 550cc injectors and a large 5th injector. I will size the 5th according to what I have left over from using stock fuel lines. I have the manifold and are doing a parallel fuel line on it and will feed the 5th injector from the return lines. Of course all this will require a retune and then there is the matter of wiring in the 5th. Is it going to be a mission?

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According to general calculations, 550cc injectors are good for about 440hp.  This should also require a return of about 2.25 l/minute at full boost fuel pressure.  Have you measured your fuel flow at full boost fuel pressure?  From what I have seen, It takes a pretty modified EJ20 to get 440hp!  Alost of guys will think this is possible until they get on the dyno.  Even heavily modified race EJ20's will usually only acheive 400hp in street driveable fashion.  As far as the fifth injector goes, I personally think it is a waste of time (my opinion only).  It will make tuning difficult and really needs a special staged injection to control it only under power.  Many a man has tried to run additional injectors and had to give up in frustration trying to get a combination of correct AFR's, good idle and smooth transition.  In short, yes, it will be a mission.  Run the smallest 4 injectors required to make enough power that will ensure you can still get good idle and cruise injection control.  Bigger injectors DO NOT equal more power! 

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  • 3 weeks later...

Hmmm, not sure about the 2.5 litre per hour pump.  I would think you would need more like 2.5 litre per minute at about 60 psi.   I would be surprised if you required any more than 550cc injectors.  There is no harm in running them at a high duty cycle at full power (if that is as much power as you are ever planning on getting!).  Like I said having injectors that are too big will limit your ability to have good idle, cruise and economy (something that is often ignored and results in a car you never want to use!).  The first thing you should do is upgrade the fuel delivery system.  Standard lines will be fine.  Install a good quality (not a cheap) pump like a Bosch motorsport pump. 

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I have had an aquamist installed for a year now. Probably got ahead of myself and should have spent the money on something else (FMIC, new engine, etc) but it seems to do the job well. I have a stock wrx mill with TMIC and a VF23 and its putting out 213kw with the grey top injectors. Frustrating thing was getting it tuned, no one seems to know what to do with it.

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Yup, you can spend all the money in the world on bits, but in the end it comes down to how good the tuner is as to the final result.  Most tuners can get you a good power figure, but only the good ones can make the car have good power and be pleasent to drive!  I would be interested in seeing a dyno run with water injection off then on!

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