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Thread: The Single Turbo Conversion Thread 4.0 (2022)

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    The Single Turbo Conversion Thread 4.0 (2022)

    G'day. I wrote this thread back in 2008 on my local subaru club forums, and since joining here I've seen quite a bit of discussion on the twin turbo's, and converting them to single, which is a change from you get on some other forums. So I thought this might go down well here. Just a few notes though, I do live in New Zealand, which is one of those little JDM paradises, so parts for the conversion were allot easier for me to get, and allot cheaper too (or not as the case may be sometimes ). It's quite infromal, and probably still riddled with spelling and grammatical errors, but hey.. gets the point across

    Also, this conversion thread assumes you are starting with a GTB already. can still be used to convert a 20R for a drop into a USDM car too though, there just may be some extra parts to get. and problems with the whole LHD thing..

    I have come back and re-written much of this thread in 2022, much has changed over the years. It's a crazy world we live now where GC8's go for 80+k. But SF5A foresters don't. So pillage then for their juicy single turbo parts when you can.
    Last edited by Reuben; 06-19-2022 at 06:47 AM. Reason: 2022 revision
    Single turbo conversion, "How to" can be found here
    JDM 1998 BG Legacy GTB Limited, EJ20K STi swapped
    JDM 1990 BC Legacy Ti type S, EJ25D swapped
    JDM 1995 BG Legacy 250T, EJ20D swapped
    JDM 1989 BC VZ-R, Stock - Dead now

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    Dirt Tech / Vendor Reuben's Avatar
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    1. Introduction.

    This thread has been made to store all the tips, tricks, and how-to's on the Legacy Twin Turbo, to single turbo conversion. The following content is based on my conversion in 2007, with some research from various forums, and other people who have done the conversion before me, and since me. This thread is specifically aimed at the B and C revisions of the BG5/BD5 Legacy, that have the EJ20R motor. However this doesn't stop you from gaining a bit of knowledge on the how to's of this conversion. I ask you to please read the entire thread through before getting started too. I will be assuming you will be lifting your engine for this, and assuming you know how. It will make life a whole lot more easy for you. And lastly, this is only a rough guide, with a few pointers in it, not a manual or complete instruction set. Please remember that! If you get stuck, figure it out!

    And from hereafter I'll be using "V3/4" to simple refer to Version 3 and 4 WRX's, and STi's, and Foresters with the same engine (EJ20K/EJ20G).

    First thing you'll need is a shopping list, this stuff is getting hard to find now! but with luck, you'll find it all. I've tried to list every last washer and rubber pipe and bottle of fluid, so you don't get any hidden costs, and can run a tight budget. Item's marked with an * are required, anything not market, you can bodge or fab or use the TT one.


    This list applies to the EJ20R conversion:

    *A Version 3/4 EJ20K ECU (1S, 6S, 75) Or stand alone ECU like a link or haltec (this is the preferred method these days as these sensors are getting OLD now.)
    *A turbo. (Stock single scrolls of the era that are a good match for the 6S and 20R heads: VF22, 23, 24, 28, 30, 34, 39)
    Single turbo Coolant supply and return lines. You can make your own (Feed: 21144AA020) (Return: 21144AA080)
    Single turbo Coolant supply pipe (14423AA021)
    Single turbo Oil return line (rubber hose) (807515712)
    Single turbo Oil return pipe (Metal pipe in block).
    *Single turbo exhaust manifold. A 2.5L equal length one works too, and offers better fuel economy. But you won't get that boxer rumble

    *Up-pipe
    *Downpipe.
    *Single turbo gear box cross member. Needed if you get a bolt on DP, not if you make your own downpipe.
    Single turbo up-pipe bracket. (the one by the turbo)
    *Single turbo intercooler Y pipe. Anything from V3/4 and 5/6 will work
    *Turbo outlet to Y pipe hose (Part of Y-Pipe normally)
    V3/4 Intake manifold, complete. If you do not get a complete one, here is what you'll need for it:
    Idle control valve pipe (metal thing that goes on top of the manifold)
    BOV
    BOV Return line/rockercover breather lines (Don't forget the little rubber hoses that connect it to the rockercovers!)(it's a metal pipe hidden on the underside of the manifold)
    *V3/4 Turbo Inlet/intake pipe
    Crank case breather hoses (Stand off: 807519082, Tee piece: 11821AA460, From Tee to PCV: 99071AA360, From Tee to intake: 807512271)
    Right hand fuel rail if you want to do the split fuel rail, more on that later
    V3-6 Heater core pipes. These pipes go from the water pump, up the side of the head, across the top of the engine, and up to the clutch housing, made of metal pipes, and joining rubber pipes. (14065AA010)
    V3-6 Heater core hoses, these go from the pipes by the clutch housing, to the firewall. (Heater inlet: 72411FA001, Heater outlet: 72015AA020)
    *2 meters of vac line. You can make do with the leftovers from the TT system however. Budget for this anyway
    Single turbo solenoid bracket (This is so you can replace the BBoD)
    Pressure select solenoid (a 3 port solenoid from a single turbo, this is only to tidy up the wiring, you actually already have one in the BBoD that you can use - but it has a great big plug with like 15 wires.)
    Bolts to block off the primary turbo's Oil supply, return and coolant return lines on the left hand head. You can pick these off N/A's are Pick-A-Part!
    Gaskets for:
    *Intake manifold (14035AA281 x2)
    *Exhaust manifold (14038AA000 x2)
    *Turbo/up-pipe (44022AA150)
    *Turbo/downpipe (44022AA180)
    Coolant
    Oil
    Oil filter (15208AA100) + Sump plug washer (11126AA000)


    If you wish to do the split fuel rail mod while you're at it;
    8 feet of EFI (Electronic Fuel Injection) hose. 8 ft really is just enough.
    A few hose clamps (6 should do it, you can reuse the originals for the rest)
    2 T sections
    A second right hand fuel rail, with luck you picked one up with the intake manifold

    Coil pack mod (to make it look like a real V3/4):
    Any phase-1 Coil pack (And loom plugs).
    V3/4 Leads
    V3/4 Ignitor (And loom plugs), or one from a BG N/A
    Some wire for making new loom coil pack loom


    For other models:
    For BG5A owners - This list applies to you also, only, you probably need to run a WRX ecu, not an STi ECU.
    For BE/BH owners, of the Rev A, B and C variety, you can pretty must use this list too, but for anything labeled v3/4, sub out for v5/6. ECU wise you won't be able to use an STi ECU, the STi ECU has trouble dealing with the higher compression, so you either need to run a WRX ECU, an aftermarket ECU, or lower the compression somehow (if you're also rebuilding the motor).

    For BE/BH Rev D owners... You're using all V7/8 gear. The Rev D is a special beast. It's all "Phase-3" gear (V7/bugeye and up), but without AVCS. So yeah, you'll figure it out.
    Last edited by Reuben; 06-19-2022 at 01:13 AM.
    Single turbo conversion, "How to" can be found here
    JDM 1998 BG Legacy GTB Limited, EJ20K STi swapped
    JDM 1990 BC Legacy Ti type S, EJ25D swapped
    JDM 1995 BG Legacy 250T, EJ20D swapped
    JDM 1989 BC VZ-R, Stock - Dead now

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    2. Getting Started.

    As mentioned above, I said I'll be assuming you will be lifting the engine for the conversion. You don't actually have to, but it will make life for you a WHOLE lot easier! I'm going to skip how to do it for this thread though.

    If this is your first turbo engine pull, remember these are pull clutches, so you gotta remove the starter, and pull the clutch pivot pin out.

    Once you have bought all the bits you need, Rip into it! You'll need to take your intake manifold off, your downpipes off, exhaust manifold and turbos. up to you which order. You also need to swap the gear box cross member over if you're getting a bolt on downpipe. You'll want to drain your oil, and coolant too.

    Engine outskies!



    I like to take out the BBoD early on












    Last edited by Reuben; 06-19-2022 at 01:25 AM.
    Single turbo conversion, "How to" can be found here
    JDM 1998 BG Legacy GTB Limited, EJ20K STi swapped
    JDM 1990 BC Legacy Ti type S, EJ25D swapped
    JDM 1995 BG Legacy 250T, EJ20D swapped
    JDM 1989 BC VZ-R, Stock - Dead now

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    3. The conversion part 1. Block, heads, and turbo.

    Now, the conversion can begin.
    Start by taking the intake manifold off. Try your best not to snap the breather line that goes to the crank case breather off, so you can sell the intake charge pipe to a twin turbo chump for some cash-back.

    Get rid of everything on the left side (passengers side) of the engine that is to do with the primary turbo. This includes brackets, turbo, turbo oil supply and return lines, and coolant supply and return lines. The oil supply is in an odd place behind the cambelt, but you can get to it without taking the cambelt off. Blank the oil return and supply with a bolt, and fresh copper washer. The coolant return is also an easy one to block off with a bolt, but unfortunatelly the oil return is a right old bitch. Some pics of these steps:
















    You can either shove a bolt in a hose for the oil return like we did on my mates motor, or you can pull the old return out and weld/braze it shut like we did on mine. Other option could be a frost plug, but I couldn't find any that fit. 15mm was a loose fit, 16mm didn't fit, so it's probably 5/8" which is super odd... On a japanese car!?







    Now, onto the primary side.

    Turbo oil supply - you can keep and use the TT's
    Turbo oil return/drail - you need to use a single turbo oil return line, EJ20G/K is what you want, but EJ205 should be the same at a guess, this is not available from subaru (looks like it's only supplied with the cyl head), so pick one up from the junk yards.

    Turbo coolant supply - you use some universal hose, or get a turbo a single turbo one (21144AA020 and 14423AA021).

    Turbo coolant return line - you can use some universal hose, but it's still available new from subaru (21144AA080 for VF22, 23, 24, 28) (99078AA073 for VF30, 34, 39)












    ^^ Showing the difference between the TT cooland supply, and Single T. Single turbo takes up less room and looks tidier.

    Once you have the coolant and oil returns sorted... It's time to address the heater core lines! The problem with the TT heater core hoses is that both go up and over the top of the clutch housing. When you stick a single turbo intercooler on, the Y-pipe pinches them, and rubs them, and eventually eats through them! You need to put on single turbo pipes that go around to the side of the clutch housing. The problem is, this means you must also get the metal pipes that run all the way down to the water pump. They look like this. The lower left is the twin turbo one, the upper right is single turbo. Note how the single turbo pipe shoots off and out of the way. You can still buy these pipes new from subaru. Make sure you also get the little pipes that go up to the throttle body.

    14065AA010 - Main pipes
    807607241 - Main to bell housing pipe
    14065AA090 - Bell housing pipe

    807907282 - Bell housing pipe to throttle
    807907272 - Throttle to IACV
    807607180 - IACV back to main pipes
    Get em while you still can!




    Time to stick on the exhaust manifold, and up-pipe. With that in place, on goes the turbo brackets. I recomend you at least get the small one. With none, vibration makes short work of the up-pipe felxijoins! Now stick on the turbo! Make sure you use a new rubber hose for the turbo oil return/drain (807515712).







    Then on goes the intercooler bracket... The intercooler bracket conflicted with the turbo outlet on my setup, I used a VF39.. The later turbo's outlets point towards the back more (I think anything of single scroll with fly-by-wire, The older ones (VF24/23/22 etc) point forward and don't have issues. the angle grinder fixed that.




    Check over the engine and make sure everything engine wise is delt to. Next up is the intake manifold and vacuum system.
    Last edited by Reuben; 06-19-2022 at 03:40 AM.
    Single turbo conversion, "How to" can be found here
    JDM 1998 BG Legacy GTB Limited, EJ20K STi swapped
    JDM 1990 BC Legacy Ti type S, EJ25D swapped
    JDM 1995 BG Legacy 250T, EJ20D swapped
    JDM 1989 BC VZ-R, Stock - Dead now

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    4. The conversion part 2. Manifold and reassembly

    Right, now to deal with the intake manifold. Strip the TT manifold of all it has. Take photo's of how the loom is arranged. Also, if you break this, don't worry. leave the vac lines off it, it's not needed. But leave it plugged in so you don't get a CEL (It's the evap solenoid, it's to do with emissions, it goes off to the charcoal cannister)


    You don't NEED to put the BOV return hose on under here, but I recommend it. Going for atmosphere vent does have side effects, so if you can, put the pipe in now so you can run a 50/50 BOV in future.
    The other reason to run the BOV return hose is that it has the rocker cover breather hoses, so it tucks them tidy under the manfiold, instead of over the top like TT.
    If you're not using a single turbo BOV return/breather setup, you can mod the TT breathers and just use them. It's a bit ugly though, but these days and in America you may have no choice.
    Fit the inlet charge pipe. If you bought a silicone one, the cheap ones will need trimming, which is manifold on and off several times, so do this now.
    If you're slapping on a complete EJ20G/K manifold, be sure to transfer over the bracket that holds the throttle cable from the EJ20R manifold.





    Pictured with a split fuel rail mod, this is not needed if you run a modern fuel pump. Please do upgrade the fuel pump. Split fuel rails ware a cheaper easier mod back in the day, but with 20K's and G's getting thin on the ground now to steal rails off, and modern fuel pumps being so cheap, it's a redundant mod now. The idea was cyl 3 wouldn't run lean when you put the boost up with the stock pump. But if you got a good pump, this wont happen anyway.












    Ok, so now we have a complete single turbo intake manifold of some description, put the sucker back on the engine and ensure you connect everything up, like the crank case breathers and purge control solenoid (that green thing you broke... )


    With regards to the engine harness, thankfully, EJ20R's, and EJ20K's are extremely similar engines. And it's interesting to note, the single turbo engine loom just plugs straight in! We tested all the pins for matts conversion (as he used a single turbo engine loom, wheres I used the TT engine loom), and it all matches up. The differences are... No ignition 3 and 4, since wasted spark. If you are using an EJ20G/K harness, you will need to splice in an igniter somewhere, as these are inbuilt into the coils on the 20R, so there is no separate igniter in the legacy.

    What we did, was just add the ignitor into the engine loom. Easy. More on the coil pack conversion later in the electrical section!


    Sweet, that's simple aint it. Engine done and dusted! Hardly any work at all is it . And this coming from a damn n00b ;D
    Now give the engine a once over, check everything is in order, all things plugged in, all lines plummed correctly etc. Now you can drop the engine back in, and move on to the next step.





















    5. The conversion part 3. Vacuum lines and the BBoD

    There are a few things to note at this point. You'll be wanting to pop the intercooler back on by now, but just remember this. The line that goes from the water pump to the heater core on a V3/4 runs around the side of the bell housing, but in the TT's it runs up and over right where the intercooler Y pipe wants to be (would normally go between the two TT intercooler pipes). As mentioned earlier, I don't recommend you keep the TT heater hose setup, change this to be like single turbo and scoot around the bell housing. Don't forget about the O2 sensor either, the TT's one will stretch over from the battery area and fit behind the turbo just fine, but putting the intercooler back on can stretch the wire, I'm lucky mine didn't tear off... Just give it pleanty of slack turbo side before putting the intercooler back on, and you'll be fine.

    Right, onto the Black Box of Dooooom! Oh noes! ... It's actually pretty simple really... Jason (the OG single converter circa 2004 ish) showed me the pic below when I had to do it, it's really all I needed. Basically make your solenoid box look like the one below, and you're set. Now, in the shopping list I said to get a "Single turbo solenoid bracket" and "Pressure select solenoid". While you don't have to, it just makes the TT conversion that much more complete. The bracket I said to get for obvious cosmetic reasons, the solenoid, just so you can lose the big whore of a plug with a mess of wires coming out of it that you won't using any more. The picture of my end result shows this well. Note, I used a Gen 1 legacy bracket! Any work, the V3/4 ones are shaped different, and sort of, look and flow better. But I like my gen 1 bracket, bit of a homage to papa legacy!



    ALL HAIL THE SPAGHETTI MONSTER















    Here I have a few extra lines for an electronic sender for the Defi boost gauge I put on the solenoid bracket. And I'm using a HKS EVC3 boost controller, which is a 3-port, not 2-port soneloid. Meaning no tee at the turbo, instead you have a line from the turbo out let to the solenoid, a line from the solenoid to the wastegate, and the bleed line back to the inlet.


    The vac lines in a single turbo serve two functions

    1. Boost control
    . MAP

    *For a 2-port boost control solenoid (BCS), on the turbo is a vac hose going direct from outlet to wastegate actuator, with a pill in the line, and a t-section. Leave the pill in, and run a vac line from the T to the BCS. The second port on the solenoid is the bleed, and that goes back to the inlet pipe pre turbo, but after the MAF.
    *For a 3-port solenoid, there is no tee at the turbo, and no restrictor pills. You have one vac line from turbo outlet to solenoid, one from solenoid to wastegate (soime aftermakets have 2 to the gate), and your return to the inlet pipe.
    *For MAP, you have a hose off the manifold that goes to the pressure select solenoid, then a little hose from the solenoid to the MAP sensor. The stock ECU uses the select solenoid to toggle between manifold pressure and atmospheric pressure. Most aftermarket stand alone ECU's will have an atmosphere sensor on the boards, so don't use select solenoids. Haltech even has the MAP sensor on the board, so you can run a vac line to the cabin instead of the solenoid bracket as pictured.


    I'll point out now, an oddity with the legacy car loom here. The pin the single turbo ECU uses to talk to the boost control solenoid is indeed the same as the Legacy TT ECU's BCS pin. However, that wee BCS wire doesn't go to the BBoD, it goes to the passenger side fender, where the TT's BCS lies. The wire that talks to the duty solenoid in the BBoD is actually a different pin in the Legacy ECU (Exhaust valve duty solenoid, to be exact, the BBoD BCS controls the secondary exhaust valve). How to fix this is in the wiring guide coming up next.

    Now that's pretty much it. Put everything back in the engine bay make sure EVERYTHING is plugged in, like radiator fans, starter motor ground wires etc. etc. and put that intercooler on. If you used a new gen turbo, like a VF39, you'll have to trim some of the long end off of the silicone part of the Y-Pipe to fit it (Short end goes to the turbo). I took about 30mm off mine in the end, and it was still a tight squeeze, but it's entirely possible.

    Ta-da, all done. Now the fun part, the ECU wiring.





    Last edited by Reuben; 06-19-2022 at 05:27 AM.
    Single turbo conversion, "How to" can be found here
    JDM 1998 BG Legacy GTB Limited, EJ20K STi swapped
    JDM 1990 BC Legacy Ti type S, EJ25D swapped
    JDM 1995 BG Legacy 250T, EJ20D swapped
    JDM 1989 BC VZ-R, Stock - Dead now

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    6. Wiring.

    6.1. ECU.

    There is many different pinouts for TT. About 5 in fact

    *2nd gen A-rev (pre-facelift) - "4-plug"
    *2nd gen B/C-rev MANUAL (facelift) "3-plug"
    *2nd gen B/C-rev AUTO (facelift) "1-plug"
    *3rd gen A/B/C-rev (pre facelift)
    *3rd gen D-rev (facelift)

    For BG/BD A-revs 4-plug:

    Fuck that shit, just get a wire in stand alone ECU. Honestly. Don't fuck around with these near 30 year old sensors, just get a Link/Haltec

    Here's a picture of what pain and suffering looks like:





    For BG/BD B/C-rev MANUAL 3-plug:



    To get at the ECU, it's in the passenger foot well.










    (don't mind the sequential controller in this pic, was taken before I singled)




    Take the plugs out, and you will see what is shown on the pinouts









    Wire A9 (loom) into A10 (ECU). Wire A22 and A23 (loom) into A9 (ECU). Ground B18 (ECU).
    Swap A19 with A3 <- makes V3/4 ECU talk to the correct boost control solenoid.

    And the not so technical drawing of the above description for us simple minded folk.




    It's that easy.

    Now do note, the joing of A9 and 10 into A10, and Joing of A22 and 23 into A9... This is what we do to make the factory legacy Ignitor-on-Coil-On-Plug setup run wasted spark. You do not need to do it if you do the following coil pack conversion. I wiried mine as above, and ran like that for nearly 2 years, before doing the coil pack conversion. So it works just fine! and is the cheap and easy alternative to the coil pack conversion, and a lot of people prefer the coil on plug anyway.


    For BG/BD B/C-rev AUTO 1-plug

    Refer to A-rev instructions. (get a Link/Haltech)

    For BE/BH A/B/C-rev



    You also need to bybass the fuel pump controller in the boot. If memory serves me right (last time I did this was 13 years ago), pull the passenger side trim out of the boot, and the fuel pump controller is living in there.
    What you need to do is basically bypass it, so there's power that comes in from the fuel pump relay here, then it goes down to the pump. just snip and bridge the controller out, and same for the ground wire I think. I did have information on this, but they have been lost to the sands of time. You will also need to take the ecu pin that controls the fuel pump controller, and send that signal direct to the relay instead. If you don't do this, I'm pretty sure the fuel pump will run continuously with the ignition, not good when you're parked up listening to music, especially if you got an old walbro.

    For BE/BH D-rev

    Your wiring is basically the same as V7 STi, you won't need to touch coil wiring. But you'll have to figure out how to kill AVCS. You will want to get any STi ECU you chuck in tuned and AVCS disabled basically. Alternatively you can drop in an EJ207 and add in the AVCS wires to your bulkhead harness and march to glory.

    6.2. Coil Pack Mod.

    I've been asked to do a write up on the coil pack mod, to rid ones self of the coil on plug system, and go to the sexy, cheap, and reliable coil pack system.

    Eaaasssyyyy. You will need a Coil pack and leads off any Version 3 or 4 impreza, or N/A BG/BD. A matching 5 pin ignitor, and some additional wires and some actual loom stuff. Refer to the pictures to see what these look like!

    For the wiring, I just spliced into the engine loom to get my power and ground, and 2 ignition signals. For the power, I just stole the 12v supply that goes to the coil packs, makes enough sense. And for the ground, there's a general ground wire you can tap into. Again, the pictures show which wires I used clearly. Then from there I just made a new branch off from the loom with some wires I had lying around, dedicated to the coil pack and ignitor. It's very strait forward! I think I'll let the pics and wiring diagram do the rest of the work for me.

    For those who used the single turbo loom, It's done in much the same way, but it's slightly easier. For the single turbo loom, all you need to so is add the ignitor in, and ground it. So you cut the 2 wires off to the coil pack. From the ECU goes to the ignitor inputs, the ignitor outputs go back into the engine loom where you cut. Then simply T in a ground, and that part is done. Next, double check that the 2 ecu inputs are matched up to the pins on the ECU, I can't recall if you need to change any at the ECU end. I supect you have to put A22 or 23 into A9 or something like that. It should just work if you have already wired the ECU for coil-on-plug like above.

















    Last edited by Reuben; 06-19-2022 at 06:16 AM.
    Single turbo conversion, "How to" can be found here
    JDM 1998 BG Legacy GTB Limited, EJ20K STi swapped
    JDM 1990 BC Legacy Ti type S, EJ25D swapped
    JDM 1995 BG Legacy 250T, EJ20D swapped
    JDM 1989 BC VZ-R, Stock - Dead now

  7. #7
    Dirt Tech / Vendor Reuben's Avatar
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    7. Epilogue and Notes.

    Well. What can I say. It's one of those projects that start out seeming fairly simple... then get very complicated... But once you're done, it actually seemed quite easy... ??? It took me a week first time round. I hope that my shopping list will allow you to gather every last piece you need before even starting. I have done about 4 single conversions since writing this thread, and if you got your ducks line up, it's a weekend job, but one week max.


    You can't run a single turbo on a twin turbo ECU, it will spit fault codes at you like a monkey on crack. Long story short, they TT ECU's constantly sample and compare boost to RPM and load, and go into limp mode when they don't see secondary come alive after 5000rpm.

    It's a fun project, and it removes the restrictions that twin turbo lay down on you. You can mod a single turbo to your heats content, the ECU's are dumb, and just take it, unlike TT's. Bigger turbo? Sure! Cool intake? Go for gold! Single turbo opens the world up.


    Notes:
    Version 5/6 intercoolers do not fit V3/4 Intake manifolds. Their BOV, or aftermarket BOV flange conflicts with the 3/4's idle control valve. While it is possible to make a custom bracket to fit, it will be a source of pain for you. Also, a switch to either a V3/4 or 5/6 STi intercooler will require you to find a V3/4 Intercooler bracket (yep, V3/4 bracket to fit a V5/6 intercooler). These are hard buggers to find, I ended up driving 150km's (return) to waiuku to get one from the wrecker there, at a cost of $25 (and probably $50 in fuel at todays prices)

    On the above intercooler 'drama' as my mate Jase likes to call it (he wanted me to add this one in). It can be solved by simply buying a front mount. Remember that your car, (to anyone behind a counter), is now a Version 3 STi, and any part that can fit a GC8 wrx, will fit your legacy. Jason got a GC8 bolt on FMIC kit for his legacy when he did the conversion, and that was drama free (as far as FMIC kits are concerned anyway). He lost a fog light to it though (it couldn't fit past the GTB's foggie) and he needed a single turbo coolant over flow tank though (easy peasy to get from a pick-a-part). The downside is this can add another grand to the conversion easily.

    Prepare to spend exorbitant amounts for seemingly benign parts from wreckers. For example, that little pipe that goes from the turbo intake pipe, to the ICV cost me $45 from a wrecker! Simply cause it was obscure, and he saw that I HAD to get one. It would have been something like $5 from a Pick-a-part, but none had the applicable model WRX's for my conversion at the time. The fact that no V3/4 WRX's/STi's were at any Pick-A-Part in Auckland probably raised the budget of the conversion by a few hundred dollars at least. I wish you luck ever finding one that lasts for more than a few days... I still managed to squeeze through the whole project at under $1500 though. (not including things like oil, tools, and crane hire; that all went under the rebuild budget wink.gif) <- this was written in 2009, SF5A fozzies still pop up in pick-a-part, I got a manifold off one in chch in 2022, but these parts are going to be a cunt to get in future. The face of single conversions in future is going to be all about custom pipes and fab work. I added in subie part numbers in this 2022 revision for the hoses and pipes still available, but many of these will go the way of the dodo VERY SOON. Get on that shit while you can!

    The heater hoses are fine in the TT engine bay, they do work with a single turbo TMIC. But that doesn't stop you finding the line that goes to the water pump from a V3/4, it would make the whole lot go together much more smoothly.
    Update: I've heard twice now, of TT heater hoses rubbing through and bursting! I now STRONGLY advised you convert to the single turbo style heater hoses (this requires getting the metal pipes that go all the way to the water pump). Turns out I simply got lucky with mine, and the settled before they burst. They were working for 9 years in their squished state just fine (But I did eventually swap em to single turbo)

    The turbo oil return... This could quite possibly be the most annoying thing to source. Any old school single turbo subaru will have one, and there'll always be a single turb of some description at a pick-a-part (gen 1 leggy's, and V1/2 wrx's) (2022 reuben speaking... HAH. HAHAHA. This shits getting RARE cunts). Basically just hammer the things base a few times to loosen it up, then hammer it left and right and jimmy it out. It's very easy to break, you saw the picks of the primary side one I tried to take out... Alternately you can heat up the block and try loosen it up like that as ben did to get mine out.

    A GC WRX midpipe WILL fit your BG, no matter what the twat behind the counter says (you just need to lengthen it by about 5-10cm's, and change a hanger). (2022 reuben here... Imagine being able to buy a GC exhaust over the counter now, hah!)

    If you break the charcoal canister, don't worry, you don't need it. It connects to the purge control solenoid on the intake manifold that you can break very easily too. Besides, it's a waste of vac line hooking it up, because the factory rail it has, is thrown out the with the factory fuel rails! I bitched about doing the right thing and getting obscure brackets for the turbo. This, this is different, it's useless. You will just get to smell petrol fumes every now and then, which I love anyway.

    If you have a manual with 20H and a 4-plug ECU, you can use an EJ20G ECU, but there's about 10 or 15 wires you need to re-pin. Most wires are fine. If you have a BH/BE prefacelift Your engine I think is more or less very similar to the V5/6 STi engines.
    Update: We have found the compression is higher in the EJ208 (8.5:1 A/B rev, 9:1 C/D-rev) than the EJ207, High enough that detonation is unavoidable. You either need to drop some thicker HG's in, redo your short block, or run an aftermarket ECU with custom tune, or use a forester EJ205 ECU.


    Credits:

    Thanks to Jason (FastFour) from clubsub and Paul (ScoobyDoo) from clubsub for advice and info on the single conversion. And to the websites I stole the wiring diagrams from.
    And a big big thank you to Cameron for helping me out and doing most the work wink.gif, and to Ryan (Boostin) from clubsub for helping me tear apart the engine, and put it back together! Also to Ben (Rex_in) from clubsub for the oil drain and help, and to David (Miller) for your help too biggrin.gif And to everyone else who helped me at some stage. You are (were) all what make (made) club sub a great place

    Some more pics circa 2009

    Matts:











    Mine and matts:




    Beast 2008:





    Beast 2009:



    Beast 2014:




    Beast and Blighter circa 2019

    Last edited by Reuben; 06-19-2022 at 07:06 AM.
    Single turbo conversion, "How to" can be found here
    JDM 1998 BG Legacy GTB Limited, EJ20K STi swapped
    JDM 1990 BC Legacy Ti type S, EJ25D swapped
    JDM 1995 BG Legacy 250T, EJ20D swapped
    JDM 1989 BC VZ-R, Stock - Dead now

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    Dirt Tech / Vendor Reuben's Avatar
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    It's occured to me some who will be using this thread will be in america, with a twin turbo engine from a GTB sitting in front of them, thinking "Great, where to start!"

    I'll just make it clear that there are two types of GTB engines, one from the manual, one from the auto. The auto ones are simple EJ20H's, and are not compatible with V3/4 STI parts! For example, it has grey top injectors, instead of yellow top, and so you can't use the V3/4 STi ECU (which uses yellow tops). You can't use the V3/4 ECU anyway, cause they are 3 plug ECU's. The 20H's are 1 plug (auto) or 4 plug (manual) ECU's. If you want to use a 20H, an aftermarket ECU, and injector upgrade are a must. Good luck finding side feed's that'll fit!

    If you want to tell if an engine is an R or H, simply look at said injectors and ECU's. I strongly recoment you hold out till you can find a 20R, the H's are really not worth bothering with, an old EJ22T is a far far FAR better engine to go with! The 20R on the other hand is quite a good little engine, and can make 240hp at the wheels with a stock setup easy (At 20 psi though, that, i can prove ).

    Don't run 20 psi on a 20R that has not been rebuilt. Very bad and expensive idea...
    Single turbo conversion, "How to" can be found here
    JDM 1998 BG Legacy GTB Limited, EJ20K STi swapped
    JDM 1990 BC Legacy Ti type S, EJ25D swapped
    JDM 1995 BG Legacy 250T, EJ20D swapped
    JDM 1989 BC VZ-R, Stock - Dead now

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    Cone Eater
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    that's good info, there's plenty of people looking at the ej20tt's on ebay and importers and wondering how to convert it to a single turbo properly (not just Legacy people).

    FWIW, I'm using a FMIC kit from a WRX Very little work was involved to get it to fit my BE as well (thanks to a baja owner for confirming my suspicion by actually doing it) Had to lengthen one pipe on the passenger side fender and that was it.
    2005 Outback XT
    2003 Legacy L "Special" Edition...RIP CLICK HERE

    GO > Show. Every time.

    STI is the new medically accepted term for STD.

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    Dirt Tech / Vendor Reuben's Avatar
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    Getting the engine to fit in an engine bay? Hehe, an EJ20 will fit in ANY Legacy, Outback, Impreza, forrester, or tribeca engine bay. That's the great thing about em
    Single turbo conversion, "How to" can be found here
    JDM 1998 BG Legacy GTB Limited, EJ20K STi swapped
    JDM 1990 BC Legacy Ti type S, EJ25D swapped
    JDM 1995 BG Legacy 250T, EJ20D swapped
    JDM 1989 BC VZ-R, Stock - Dead now

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    Quote Originally Posted by Reuben
    Getting the engine to fit in an engine bay? Hehe, an EJ20 will fit in ANY Legacy, Outback, Impreza, forrester, or tribeca engine bay. That's the great thing about em
    the ej20tt's (H/R/etc) are about 800-1000 USD cheaper to get here than a USDM ej205, but since it's going to be put into a LHD car when it was made for RHD, there's always questions about fit and inevitably how to convert it to single turbo because it turns out to be a hassle to get the turbo setup to fit with the steering rack on the wrong side
    2005 Outback XT
    2003 Legacy L "Special" Edition...RIP CLICK HERE

    GO > Show. Every time.

    STI is the new medically accepted term for STD.

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    Dirt Tech / Vendor Reuben's Avatar
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    Yeah, I forgot about that, lol. Having owned a TT, and converted it; weather or not a primary turbo wants to play touchy feely with the steering setup would be the very very last of my concerns with the engine. I can only imagine setting up a TT would be a night mare and a half regardless. Going single turbo makes life SO much easier...
    Single turbo conversion, "How to" can be found here
    JDM 1998 BG Legacy GTB Limited, EJ20K STi swapped
    JDM 1990 BC Legacy Ti type S, EJ25D swapped
    JDM 1995 BG Legacy 250T, EJ20D swapped
    JDM 1989 BC VZ-R, Stock - Dead now

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    Re: Twin to single turbo conversion, tips tricks and how-to'

    good write up man. I used to have an EJ206 in my Liberty from a Gen 3 GT-B which i converted to single when we put it in. it eventually went bang so decided to go a EJ205 from an AUDM WRX which we rebuilt with forged goodies instead. Most people over here convert their twins to single anyway as it's a much more reliable system with lots of tuning options

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    Dirt Tech / Vendor Reuben's Avatar
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    Revised for 2022

    Re-hosted all images.
    Bunch of genuine part numbers added.

    Good luck all, parts are getting hard to find. Buy genuine while you still can.
    Single turbo conversion, "How to" can be found here
    JDM 1998 BG Legacy GTB Limited, EJ20K STi swapped
    JDM 1990 BC Legacy Ti type S, EJ25D swapped
    JDM 1995 BG Legacy 250T, EJ20D swapped
    JDM 1989 BC VZ-R, Stock - Dead now

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