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99rs-t
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Discussion Starter · #1 · (Edited)
kind of need a quick answer on this for the morning...but i am running wrx light blue 440s with a walbro 255 and a aromotive fpr..tuning this on a afc and [email protected] 7psi boost..what should i set my fuel pressure at? running? with vaccume on??off??i tried using some fuel caculatrs but i dont understand them..
 

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Well stock should be around 40-44psi. IIRC the stock pressure is 3bar=43.5psi.

I know with the older yellow top injectors I had flowed tested ok and safe to use at pressures of 60psi. Higher pressure will give you a better spray pattern and higher flow. I cant say if more than 60psi is safe on your injectors so I wouldnt because if pressure delta is too high on the supply side of the injector it might not open or close or do either correctly.


Heres the deal with fuel pressure. The pressure on the supply side and the the manifold side of the injector are different. Here is a good example. If rail pressure is 44psi and you are at WOT the pressure in the manifold will be very close to atmosphereic so the delta across the injectors is 44psi. Not this is the part people get confused. When you go into boost the manifold might be a 20psi. Well the rail pressure has to be at 64psi to maintain the 44psi basic fuel pressure. The same is true when the manifold is in vacuum. The rail pressure will drop because the manifold has less than atmospheric pressure.

In short adjust the regulator without vacuum or pressure on it. This will be base rail pressure.
 
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