Hello, it's my first post on these forums.

I've been modding my 1999 WRX for E85. Goal was set to +300whp (I'm afraid my 5 speed would not want more )

Mods so far, at least the ones I could remember right now
Td05-16g
EL headers
full 3" exhaust
1000cc injectors
Link G4+ plugin ECU
AEM 320lph E85 fuel pump
Adjustable FPR
Supertech forged pistons & Eagle Rods

I had a dyno session recently and we were only able to hit 300 crank HP due to fuel pressure dropping under load. We were monitoring the differential fuel pressure and it was dropping as load increased. The target was 350 kPA and when it dropped to 240 kPA we decided to call it off. It did not lean out since the ECU uses differential fuel pressure compensation.

Since then I've been trying to locate the source of the problem. I have:
-Tried 3 different fuel pressure regulators
-Re-wired the fuel pump using thick wires (probably enough to support 40A) and a relay
-Verified that the fuel pressure sensor reads correctly. I also ran the FPR with raised pressure and the vacuum signal disconnected. The drop in fuel pressure was observed (see fpdrop.png)
-Changed the inline fuel filter and even tried running without it
-Checked the fuel pump assy and the pre filter. Everything seems OK. The pump is almost brand new

So pretty much the stock fuel lines are the only thing I haven't tried to swap yet. I haven't just heard them becoming a restriction at these power levels. Has anyone here found out the limits of stock fuel lines?

Could the restrictiveness of the fuel lines found out by placing a pressure sensor right after the fuel pump and compare the reading to the one at the pressure regulator?

-Timo

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For a start you should probably be running braided teflon fuel lines anyway. Maybe think about a fuel surge tank and another pump or even two (eg Bosch 044)...see attached

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No Subarus currently owned

If you were prepared to put the pressure sender at the rear with the the pump outlet, then you could measure any pressure drop between there and where the fuel pressure sensor currently is.

And by moving the sensor around you can measure the pressures and work out exactly where the pressure drop is in the system.
EG :
After the rail but before the reg,
Before the rails,
Before the filter,
Before the hardlines,

But this is alot of mucking around. It would be just as easy to replace fuel rails and hosing at the engine. The standard hardlines are capable of way more than 300hp of e85.

Are you using one of those hardline adapters to fit the different puel pressure regs?

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Doing it for all the wagons out there

Replace fuel pump with walbro 450/460. Monitor voltage and current at pump, you might be getting large voltage drop. Or surge tank setup. Dual pumps

A surge tank mounted upfront, forward of the OEM hardlines will also bypass any restriction from the tank to the front of the car. (Which i dont think is the problem at 300hp worth of e85)

I have a surge mounted upfront with a 450 in it. And have no differential pressure loss from fuel consumption. Have pressure sender monitored by Link aswell. And tuner actually remarked the fuel pressure was bang on even at high loads while on the dyno.

The car does still surge at barbs. But its not a plumbing restriction issue. I think its a too small a surge can issue.

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Doing it for all the wagons out there

There is a dude (GTleggy) I think, on here that has maxed out the standard fuel lines on a gc8. I'm pretty sure thay are good for around 600hp. That being said you would still need to replace the old rubber sections as they aren't e85 compatible.

Maybe some of them have already started to swell up causing a restriction somewhere

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Bye bye betty blue. Hello F6.

Im at 520 oem hardlines unless urs are crushed doubt its ur issue

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Have u tried a different pump?

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First of all, thanks for all of the replies. It's nice too see that people are so willing to help a new guy around here.
I've been thinking about surge tank setup but I would like to keep the trunk empty for now. Maybe one in the engine bay?


I have already started to gather stuff for new fuel lines. I'll probably go for AN8 size (I know it's an overkill for this setup).
Yes, I'm using an adapter that bolts to the place of the stock FPR. It has a 8 mm hose connection.

Surge can doesnt need to be put in a boot. I have mine up front. As does Nick73. You can fit them down the passenger side of the gearbox. Tucked under the firewall/floor where the ECU goes.

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Doing it for all the wagons out there