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Old 03-19-2009, 04:23 AM   #1
Scooby Specialist
Member#: 184324
Join Date: Jul 2008
Chapter/Region: RMIC
Location: Colorado
1999 Impreza 2.5RS

Default Built RS-T injector sizing and general questions.


I've been searching around for injectors for my car. I know a fair amount about injector sizing for rotary engines, but am at a loss for my Subaru.

Here is my build. -Its been on the road reliably for the last year, and its time to up the boost slightly while keeping drive-ability great.

Ej253 block
Je forged pistons
Pauter Rods
Knife edged and micro polished crank
ACL bearings
ARP head bolts
Delta Ground Cams
5 angle valve job
Ported and Polished and port matched
Cobb retainers and valve springs
OEM STI head gasket
OEM timing belt, waterpump, oil pump and all other belts
All OEM seals
Motor Assembeled and Machined by Greg at Millennium Motor Sports late Spring 2007
Compression: 9.2:1

TurboNetics T3/T4 .74 trim
Greddy front mount inter cooler
Synapse engineering BOV
HKS wastegate 7lb spring
Unequal length custom turbo manifold
Custom 3” inch exhaust -no cats

RC Engineering 310 saturated injector’s 91% duty cycle (running very rich)
RC fuel rail setup with parallel fuel rail conversion
Aero-Motive Rising rate FPR
Earls high flow fuel filter
Walbro 255lph fuel pump
Hydra Nemesis 2.5 ECU

-I plan to get a GM boost control solenoid, or perhaps something else to control boost. Suggestions would be welcome.
-This car is a daily driver and I have a high importance on a smooth idle and reliability. I'd like to get around 300 WHP and increase my fuel economy above ~15mpg. With how rich the car is running now I figure I can get the fuel economy up w/o much issues.

1: What injector size would meet my power goal while keeping a decent AFR at idle? I'm thinking of 550CC injectors from RC Engineering.

2: I need a method to increase boost above 6psi, and am leaning towards a GM boost control solenoid. The Hydra ECU can control boost functions if need be. Any other recommendations/comments/ suggestions?

3: Does the turbo need an oil restricter in the oil feed line, or should I not worry about it?

Thank you for any advice!
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Old 03-19-2009, 04:37 AM   #2
Scooby Specialist
Member#: 30798
Join Date: Dec 2002
Location: kansas city ks
2001 RS-T Hybrid


I would go with some RC 750's so you have some head room if you want to up the boost some more.

Are you running an internal or ewg? Either way you can use the hydra to control boost. You could also go with any one of the aftermarket units to control boost that way.

It depends on the turbo. Some like the garrett's need it and some like my Innovative have them built in. I would call turbonetics and find out for sure.
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Old 03-19-2009, 04:45 AM   #3
Scooby Specialist
Member#: 184324
Join Date: Jul 2008
Chapter/Region: RMIC
Location: Colorado
1999 Impreza 2.5RS


Can the Hydra use both High and Low impedance injectors? Which one would be better suited to my goal? The waste gate is external, and I believe the size is 44mm, but I cannot say for certain. The waste gate does merge back in the exhaust later in the downpipe.
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Old 03-19-2009, 09:46 AM   #4
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Member#: 163445
Join Date: Nov 2007
Chapter/Region: MWSOC
Location: Effingham IL (Central IL)
l33t *******
[email protected]


RC=Lucas and Lucas injectors suck balls...

I'd explore other options! trust me you will regret having a horrible idle.

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Old 03-19-2009, 12:44 PM   #5
Scooby Specialist
Member#: 49175
Join Date: Nov 2003
2004 STI


Yes, the hydra can control both low and high impedence injectors.
What is the hp potential of your turbo?

Do NOT get 750cc injectors! Get those Bosch 1000 cc injectors if you can or use RC 1000s.

The reason is, your motor is built and you may decide to upgrade to a better turbocharger for your goals. You will ultimately lose money by selling and re-buying injectors. The idle on the hydra is good, even with 1600cc injectors.

Nice build. Luv for the GC8.
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Old 03-20-2009, 02:33 AM   #6
Scooby Specialist
Member#: 184324
Join Date: Jul 2008
Chapter/Region: RMIC
Location: Colorado
1999 Impreza 2.5RS


Ok. Thanks for the advice so far!

I've made some calls and after talking to Tim at Surgeline, he highly recommends Deatsch Werks 860cc injectors. For the time being I plan to have the Hydra control the boost as well.

I've come the conclusion that I need a better catch can as well. Any thoughts about a Mr. Gasket Crankcase evacuation system? It vents crankcase fumes into the exhaust as opposed to the turbo inlet. Any other options that won't break the bank? I'm looking for more of a temp solution for the time being. I plan to get a proper air/oil separator in the next few months.
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