STI fueling question

STI fueling question

Postby 4th2ndgendennis » Wed Jul 25, 2012 9:02 pm

What fuel rails/distribution system is best for the STI?

Apparently mine is not capable at higher power levels. #3 piston keeps melting, with no sign of detonation anywhere else. Injectors already replaced, with flow sheets. Not close to maxed out on duty cycle on any of them.

Thoughts? Perrin? Cosworth? Aeromotive? Any suggestions from past experiences?
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Re: STI fueling question

Postby Chief Geek » Wed Jul 25, 2012 9:15 pm

Is this #98? If so, I know you stopped on the hill on at Okemo, but I didn't know why. Are you having more of the same problems running lean you had at Burke?
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Re: STI fueling question

Postby sachilles » Wed Jul 25, 2012 9:18 pm

#3 seem interesting on its own, as most of the go lean on #4.
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Re: STI fueling question

Postby sachilles » Wed Jul 25, 2012 9:21 pm

At the forums at www.romraider.com you'll find many folks with Subie experience relative to tunes. Lots of good info there.
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Re: STI fueling question

Postby 4th2ndgendennis » Wed Jul 25, 2012 9:22 pm

Chief Geek wrote:Is this #98? If so, I know you stopped on the hill on at Okemo, but I didn't know why. Are you having more of the same problems running lean you had at Burke?


#96 Black STI.

Burke was the vaccuum line blew off the fuel pressure regulator. Put it back on and was running ok----until #3 melted. Thought it was because of the vaccuum line, but replaced the injectors anyway, since there was no sign of detonation anywhere else. Now that I am repeating the motor build, I am thinking fuel distribution problem. Current system is Agency Power---not exactly a top brand.
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Re: STI fueling question

Postby Terry.Murphy » Thu Jul 26, 2012 1:11 pm

Subaru's come with series injector rail setups and will run best when convertered to a parallel system. The series injector setup looses fuel pressure slowly as it goes from the #1 injector to the rest. Therefore, when it gets to cyl's 3&4, the pressure has decreased and the car runs lean. I converted my fuel system to a parallel fuel rail system and the car is much more happy as I was getting lean codes in 3&4 until I did this.

http://www.ludicrous-speed.com/wiki/ind ... l_rail_mod

That is a link that I used to setup my system. There are some companies (Perrin is one that I know of) that make a parallel rail conversion but it's big bucks. The entire setup I installed ran around $200 and the most expensive part I purchased was an Aeromotive FPR for around $140, the rest were AN fittings, hose, a fuel rail adaptor, and a fuel y block.

If you want to check out my setup at Okemo I will be there. It was simple and only took an hour or so to do. I hope this helps!


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Re: STI fueling question

Postby Terry.Murphy » Thu Jul 26, 2012 1:13 pm

Crap, Scratch that.....didn't know you already had a parallel system on the car! Should have read all of the posts!


Who is tuning the car? Are they a normal Subaru tuner?
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Re: STI fueling question

Postby Chief Geek » Thu Jul 26, 2012 3:05 pm

Right, #98. #96 is a later generation Dennis.

Your best Sunday radar speed at Okemo was 2nd highest of all. The only one higher is Butch and I doubt his engine would fit in anything smaller than a truck.

Fuel pressure at the injector problems is where I'd look first too.

Will the fuel rail accept fittings near the injectors? If it's easy, I'll bet adding 4 fuel pressure gauges piped as close to the injectors as possible and videoing them would provide important clues. I don't know how you or our tech inspectors feel about extra pressurized fuel lines in the cockpit though.

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Re: STI fueling question

Postby sdwarf36 » Thu Jul 26, 2012 6:55 pm

Fuel pressure at the injector problems is where I'd look first too.

If I put a .020" restrictor just after the gauge, It bet it would show plenty of pressure-but not have enough fuel to the injector.
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Re: STI fueling question

Postby Mopar 151w2 » Thu Jul 26, 2012 7:22 pm

I would consider a visual internal inspection of the fuel rails, both with and without the injectors plugged into them - as well as the feed lines to the fuel rails. Is it possible to increase the internal size of the fuel rail itself?
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