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
*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 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!
*Intake manifold ( 14035AA281 x2)
*Exhaust manifold ( 14038AA000 x2)
*Turbo/up-pipe ( 44022AA150)
*Turbo/downpipe ( 44022AA180)
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 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.