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Old 11-15-2005, 05:14 PM   #1
Exo
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Question Changed my intake manifold and having problems!

I am currently turboing my 05 RS. With using the stock Sti uppipe and downpipe my stock intake manifold was getting in the way. So I swapped it for a Sti one. Well since I am using the Sti injectors I am now running twice as rich. Has anyone done or know of a way to hook up a fuel pressure regulator? The problem I am seeing is that the fuel comes into the engine bay already split up to the driver and passenger sides. Would it work if I just combined the two to use the fuel pressure regulator then split them out again for the left and right sides? Thanks
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Old 11-15-2005, 07:57 PM   #2
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You need something to tell the ECU to pulse the injectors less - FPR isn't the right way to solve this
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Old 11-15-2005, 11:00 PM   #3
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I suggest you buy the Perfect Power from Rallitek.com I too am going turbo, but from WRX parts. (turbo, inj, intercooler) I just bought the perfect power, but am still waiting for it to arrive. You can adjust your fuel through this piggyback with a cable connected from it to your laptop. Check out the website. Or if you have any more questions, visit the rallitek forums.
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Old 11-15-2005, 11:49 PM   #4
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Heh, already got the PP installed. Cant adjust it enough. Got it running but when the gas is let off, it gets a massive fuel dump and either dies or wishes it had.
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Old 11-16-2005, 12:08 AM   #5
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Did you do anything to your bottom end? You are gonna blow that thing sky high.
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Old 11-16-2005, 01:31 AM   #6
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Quote:
Originally Posted by Exo
The problem I am seeing is that the fuel comes into the engine bay already split up to the driver and passenger sides. Would it work if I just combined the two to use the fuel pressure regulator then split them out again for the left and right sides?
Um, unless something has radically changed in the fuel system for the 05s, what you are seeing is the fuel supply and the return line. The pressurised line comes from the pump in the tank into the engine bay, passes both sides of the engine (passes under the intage manifold via metal tube), through the pressure regulator, and then the return line goes back to the tank. Definitely don't connect these together!

If this is where you're at right now, I'd suggest you probably need to do a lot more reading before you start pushing boost into your engine.

Mark.
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Old 11-16-2005, 11:32 AM   #7
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when you decellerate all rs's cut fuel. you should be seeing crazy lean condidtion when decellerating, which is normal. i max my wideband o2 when i decellerate. i think an eman would work well as you can tap each injector seperately.
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Old 11-16-2005, 11:56 AM   #8
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The problem that he is seeing is that Subaru accidentally made two fuel output lines coming out of the firewall instead of one send and one return. If his car isn't running WOT all the time, his fuel system will explode.

-Brett
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Old 11-16-2005, 01:50 PM   #9
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05 RS is now return-less?
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Old 11-16-2005, 03:03 PM   #10
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There are three fuel lines that come through the firewall.

Tank -> Fuel rails
Fuel rails -> Tank
Intake manifold bypass -> Charcoal canister
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Old 11-16-2005, 03:32 PM   #11
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the new cars went to a returnless system.

Ben
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Old 11-16-2005, 05:47 PM   #12
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Quote:
the new cars went to a returnless system
Ahhh. But why would they run two pressurised lines to the engine bay? Seems to discount the economy of running a returnless system.
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Old 11-16-2005, 06:01 PM   #13
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Unless one is a pressure line and the other goes to the charcoal canister, maybe?
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Old 11-16-2005, 06:05 PM   #14
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Yeah probably right.
He certainly doesn't want to connect them together then If he thought he was running rich before, imagine when the canister purge solenoid opened!!
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Old 11-16-2005, 11:48 PM   #15
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I don't want to connect them together. I was asking if there is a way to connect a FPR so that I can run a lower psi due to the ECU thinking that I have RS injectors when I really have Sti injectors. We got it running stoich, but after the pedal is released on a rev I am getting a massive fuel dump. I am only going to run 6 psi so I highly doubt I will blow my motor seeing as there are kits that run the same boost.
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Old 11-16-2005, 11:53 PM   #16
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Old 11-17-2005, 12:41 AM   #17
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I know you don't want to connect them together, I was just making a joke playing on some of your words in your first post

Looking at your photo, I can see the standard three metal pipes poking out from under the intake manifold. The middle one is sitting open so I can only guess that's the purge (charcol canister) line, and it's been disconnected. If that guess is right, then this is not a returnless fuel system, it's the same type as we're all used to.

As to your whole idea of lowering fuel pressure to reduce fuel delivery, even if you could rig up some sort of regulator to do it, the whole idea just doesn't work unfortunately. The rule is that flow rate through an injector varies in proportion to (pressure to the power of 0.5). That is Flow ~ Pressure^0.5.
STI injectors are roughly twice the flow rate to the RS stocks, that means to bring the flow rate back to the same (halve the rate) requires dropping the pressure to one quarter. That means fuel pressure of ~10PSI. At that pressure, injectors just don't work. They require a minimum pressure to properly atomise the fuel, at 10PSI I imagine the fuel would just dribble out.

The only way to overcome this is with some sort of additional management. The other guys here know far more than me about the various options.

Cheers,
Mark.
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Old 11-17-2005, 01:23 AM   #18
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If you are going to run at 5psi, you don't need STi injectors. Why not just step back to something just large enough for the job? You only need about 360cc to feed this. Maybe if you went down to stock WRX injectors your PP would be able to scale them ftw. I bet you could find any number of people willing to swap with you...
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Old 11-17-2005, 01:31 AM   #19
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I'm wondering why your ECU isn't pulsing the bigger injectors less anyway? Just because you change the injectors, the sensors should be telling the ECU to run less injector duty cycle.

If you want to lower your pressure in a returnless system, you have to spin the pump slower. Otherwise, you can add a return line and standard FPR to control the pressure.

As said earlier....you may wanna read up before going too far.
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Old 11-17-2005, 10:31 PM   #20
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I don't know why the ECU isn't shorting the cycle. But I will look further into that now that you have reminded me. If someone wants to trade me a WRX intake manifold for a Sti one. I am waiting. Seeing that I cant just swap injectors due to the fact that Sti injectors are side feed and WRX ones are bottom feed. (and I'm the one that needs to read up) also for further information my car is in an actual shop, I'm not the one doing the work. I'm there trying to learn. But they are as stumped at this point as I am. No one out here(the shop) seems to know what the hell a car is to a hole in his A$$. That is why I am on here asking people that would possibly be able to help. So if you dont have any real input, I request that you don't post here anymore.

Last edited by Exo; 11-19-2005 at 07:51 AM.
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Old 11-17-2005, 10:39 PM   #21
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Ever been on a forum before pal? You're gonna get guys coming in saying all sorts of crap, and in between you're gonna get people who try and help, like (oh I don't know) taking the time to write 200 words to explain with proper basis why what you're asking about can't work for you. Wouldn't care to explain why what I wrote for you doesn't address what you were asking?
Anyway, I wouldn't worry too much about people posting into your thread any more.
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Old 11-18-2005, 02:34 PM   #22
kgb
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STi injectors might be too big - send them to me please...
I think the PP might have hard time convincing the ECU to send less fuel under low loads situation - that's a problem with piggyback. Having a return-less system reduces the options you have in adjusting fuel
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