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'STI' Upgrade V3&V4 EJ20G specific


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#1 matdaymon

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Posted 17 July 2010 - 11:05 PM

Here is the basic version of the 'STi' upgrade I did to my Forester. This also can apply to EJ20G V3&V4 WRX's. I'll update with more pics at some stage and work at making it as clear as possible as time goes by. Will also post up the results of my dyno to give a clear idea on what to expect and any problems this may cause (this is by no means a guaranteed 100% safe mod, EJ20G's have different comp ratio's to EJ20K's so WILL run differently)

You'll need:
6S STi ECU (Version 3 and 4 STI, includes STi RA and Type R)
440cc 'Yellow Top' injectors (out of either a STI or GT-:lol:
Orange AFM
Zerosports intake or STi intake pipe to turbo
Either a pod filter to suit the AFM or a GTB/STI airbox (just the top half)

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6S STI ECU, found in both V3 and V4 STi's
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Zerosports intake connected to 'Orange' AFM via silicone connector hose and 'yellow' 440cc injectors

Also you'll need some form of aftermarket boost controller to tune your car for the desired boost pressure. Apparently the standard solenoid doesn't work with the 6S ECU.

How to:

Remove the battery from the car, this is needed to gain access to the fuel rail and you NEVER want to mess with the ECU with the battery still connected.

In order to get to the fuel rail on the passenger side you will need to also remove the window washer bottle so you can reach the back injector. The drivers side requires only the airbox and intake to be removed (you'll be doing this anyway) in order to reach the injector rails.

The standard injectors have harness wires plugged into them, unplug these and then unbolt the 8mm bolts which hold the injector cover in place (these can be removed with a screwdriver but using an 8mm hex socket is better).

Removing the injectors from the rail is a bit of a pain, you can be ruthless as you want if you don't plan on ever using them again, I found using a set of pliers and wiggling eventually got them out, though this ruined 3/4 of the injectors. When you remove the injectors you want to keep all the rubber O rings you will need these for when you put the yellow's in if they didn't come with any.

After you've pulled the grey injectors out use a bit of Vaseline as lube to put the yellow injectors into the rail. You don't want to force them in as you'll crush/warp the O rings. Once they're in replace covers and plugs, and washer bottle.

If you have gone with a Zerosports style intake just replace the section of the intake before the AFM with this. Plug the Orange AFM in (pretty obvious where it goes!) and replace the airbox.

The ECU is located in the passengers footwell under the carpet and behind a metal plate held in place with 10mm (?) bolts. Again, best to use a hex socket here to remove. The 6S ecu is a direct swap, just pull the factory ECU out and plug in the 3 plugs. Replace the metal plate so your passengers don't tread on your nice new ECU and replace the carpet.

That is the conversion in a nutshell. The boost controller is dependent on what you choose to use (Electronic or Tap)
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#2 boostin

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Posted 18 July 2010 - 8:49 AM

Sidenote about unplugging ECU with battery connected....

2004 GT Legacy will keep running as 2 of the 5 plugs are pulled out. It's not happy about it though... :lol:
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#3 SAVELOY SOUP...hmm

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Posted 08 April 2014 - 11:07 PM

Here is the basic version of the 'STi' upgrade I did to my Forester. This also can apply to EJ20G V3&V4 WRX's. I'll update with more pics at some stage and work at making it as clear as possible as time goes by. Will also post up the results of my dyno to give a clear idea on what to expect and any problems this may cause (this is by no means a guaranteed 100% safe mod, EJ20G's have different comp ratio's to EJ20K's so WILL run differently)


I know this was posted ages ago but, any dyno results & info on running etc?
Wouldn't mind trying this myself.

#4 matdaymon

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Posted 10 April 2014 - 1:58 AM

Here is the basic version of the 'STi' upgrade I did to my Forester. This also can apply to EJ20G V3&V4 WRX's. I'll update with more pics at some stage and work at making it as clear as possible as time goes by. Will also post up the results of my dyno to give a clear idea on what to expect and any problems this may cause (this is by no means a guaranteed 100% safe mod, EJ20G's have different comp ratio's to EJ20K's so WILL run differently)


I know this was posted ages ago but, any dyno results & info on running etc?
Wouldn't mind trying this myself.


Dyno results were pretty big in difference. Stock (with Auto trans) was 128.4KW at the wheels, with STi upgrade (and manual box) 182.4KW (I think, car is long gone and don't have dyno sheet with me, seem to remember saying 248Hp at the wheels)... NOTE: This was on two different dynos so there may be a margin of error.

Car ran fine at safe boost levels (max was set to 15.5PSI and regularly was run at 12PSI) with a good Air : Fuel ratio and drove completely fine. Suspect the reason it went to car heaven was the kid I sold it to turned up the boost which was not advised by the Dyno operator Gary Capper after the STI run.

As a sidenote, the difference in peak power between a Forester with this upgrade and stock TD04 and a Single converted GTB with VF28 turbo was less than 2 KW
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#5 Reuben

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Posted 11 April 2014 - 9:34 PM

As a sidenote, the difference in peak power between a Forester with this upgrade and stock TD04 and a Single converted GTB with VF28 turbo was less than 2 KW


Turbo size difference offset by compression ratio there is my guess. 20R's are 8:1. Nice to see that difference, spool of a TD04 but power of an STi.
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#6 matdaymon

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Posted 18 April 2014 - 10:33 PM


As a sidenote, the difference in peak power between a Forester with this upgrade and stock TD04 and a Single converted GTB with VF28 turbo was less than 2 KW


Turbo size difference offset by compression ratio there is my guess. 20R's are 8:1. Nice to see that difference, spool of a TD04 but power of an STi.


Yeah, you make peak power more in the mid range rather than in the top end with a td04. I remember it was pretty fun to ride the wave of torque rather than rev the shit out of it. Been feeling very nostalgic for a SF5A Foz lately
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