Where did you buy the fuel pump from? Was it a reputable seller or ebay. It could be an imposter.

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Doing it for all the wagons out there

How big surge tank would I need? I have some extra space in the engine bey since I'm running a japspeed FMIC. If I understood correctly the current fuel pump would feed the surge tank with low pressure & high flow. Then the pump(s) at the surge tank would actually up the pressure and feed the injectors?

Another pump will be the next thing to try.

I bought it from a local tuning shop. I'm quite positive that the pump is a genuine one.

Lately I've been noticing that car takes a few seconds to start if I don't crank it at the same time when the pump is priming. I just thought it was because of E85. The typical Finnish summer is not very warm

But I don't remember it doing this right after I changed the fuel pump. This could be related to the pressure drop problem. Maybe faulty internal by-pass valve?

I will check the pump again and report my findings

1.5L to 2L would be plenty of you were gonna do a surge can system.

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Doing it for all the wagons out there

Didn't think of that location, nice I'll keep it in mind

So, I checked the pump again. Nothing obvious wrong with it. While I was at it, I decided also I rewire the pump voltage supply wires through the service hatch. I used a ring terminal type bulkhead connectors with thick wires.

I observed a voltage drop only of 0.15 V at idle (pump terminals vs battery). Previously the drop was around 0.7 V and with all stock wiring it was much much more. I also blew compressed air through the fuel lines. Nothing came out and it seemed quite free flowing.

I put all together and went for a test drive. Did a couple of WOT pulls and according to the logs there is only about 20 kPA pressure drop now. Earlier I was seeing 40 to 50 kPA drop at WOT.

I wonder if pressure drop of this size is be expected with single in-tank pump and stock fuel lines. Regardless, I will be doing the fuel lines and hope to lessen the pressure drop even more. But right now I don't think the fuel pump is the culprit.

Stock 8mm fuel line will do/has done well over 600whp, i think even 700whp(thats well over 850fwhp) on e85 might happen.....just need a pump that can keep up.

What FPR ?

If your pump and reg work right there should be no pressure drop ... fp should be solid base setting plus map until you let go of throttle.

Put a walbro e85 pump in it ! ...does sound like pump is lazy.

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MY99 WRX EJ2.35L 720whp 9.48@147mph
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The FPR is Aeromotive style one, I believe it no be non-genuine but I've tried with three different FPRs and no change. I've opened the FPR once and checked if it has any problems associated with fakes ones but this one seems to have good quality. One of the tested FPRs has been working great on other install. Still, all of them could be bad.

I've been looking at 450lph E85 Walbro pump, but isn't that one a bit of an overkill? I'd probably have to get a controller for the pump to prevent excessive fuel heat up.

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What is your base fuel pressure set to on the fpr?

You said in your first post you were targeting 350kpa fuel pressure under load. That sounds too low.

Standard Subaru base fuel pressure is 43psi (630kpa). You would want to be close to this as a minimum starting point from a safety/tuning point of view and then tune/adjust as required.

As GtLeggy has said above the fpr should keep fuel pressure steady.

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Bye bye betty blue. Hello F6.