Downpipe -- The turbo uses a standard IHI turbo downpipe flange. The flange I originally purchased from Outback Motorsports is a 3/8" lasercut flange with exit holes for both the turbine and the wastegate. This promotes better flow and ultimately more horsepower. After meeting with Trey Cobb, he stated that the design works well, albeit TOO well. When you plumb the wastegate exhaust, unless it is on a dedicated racecar, you merge it back into the main exhaust stream about one and a half feet downstream. This keeps the turbulence down, but it also creates a vacuum acting on the wastegate exhaust. What happens is when the wastegate opens slightly, just when the wastegate starts seeing a little use, the vacuum will suck out additional exhaust gases away from the mainstream and actually cause the boost to drop. This behavior is basically the opposite of boost spiking and is detrimental to a smooth mid-range. Both Trey Cobb and Christian lean towards a collector similar to the APS or MRT units. I have decided to use the APS High-Flow Discharge Pipe which is available from Trey or Christian for about $200. This piece has a 3" outlet, so I'll be doing a 3" mandrel bent, turbo-back exhaust. The biggest restriction in the system is the turbo, not the exhaust system, so unless you need to harness every last ft/lb of torque, go as big as realistically possible so the exhaust will "get the hell out". In retrospect, a 2.5" exhaust flows well enough for up to about 380hp.

Hi-flow Cat -- Size is dependent upon dowpipe size. This is needed to prevent the check-engine light coming on for inefficient catalytic function; duh, there is no cat! Emissions is also a concern; we all need to do our part. Adding a high-flow cat will usually make your emissions system operate more efficiently than factory, with little to no performance hit. In theory, the cat will need to be installed about 4" downstream from the turbo. However, listen to what Shiv has to say,"... a cat cannot be properly installed in the turbo exhaust plumbing. Not enough room. This is why the vast majority of Minnam turbo cars are currently running around with hollowed-out cats (the improperly located and poorly sized cats clogged up within the first few months of use) But there is plenty of room for the car in the intermediate pipe, just downstream of the downpipe. I recommend doing just this." Cost will be $99.99 for a Catco cat, part number CTO-8007, from Summit Racing. A double-duty cat is recommended, otherwise you can expect to have a dead cat in a couple months.

Flex pipe -- This is usually used to prevent exhaust manifold cracking due to engine movement. Anthony Young of a WRX club states that a "flex joint is not necessary because of the boxer design of the engine" . When I have my downpipe fabricated, the fabricator will analyze my car and then determine if I need to install a flex joint or not. I believe one will go in just incase.

Turbo Brace -- When you add a turbo to the stock EJ25 headers, a brace is required due to the 3 foot torque lever the turbo would be sitting on. However, since we are using cast manifolds in a very compact area, a brace isn't necessarily needed. It definitely won't hurt to have the brace, so I will have everything bolted up then have a fabricator take a loot at the best place to brace. There are numerous open bolt holes in the transmission housing and the heads, so the possibilities are pretty limitless. The stock Legacy Turbo brace bolts onto the up-pipe flange around the turbo and then bolts into the side of the head. This brace cannot be used because the up-pipe space pushes it too far away from the head.

Intercooler -- You may use a MY93-MY96 WRX IC or any other IC made to fit 2.5RS. This is optional as I think some people have run unintercooled MY00's. Keep in mind the Legacy IHI turbo is going to be small, so there is an increased risk of detonation due to higher intake temps. I would strongly suggest an IC. I ordered my intercooler from Andrew Lord at Subaru Spares. The cost was £45.00 and the shipping was £57.00 for a total cost of $147. If you can, request the turbo->intercooler piping. This will be where the BOV will mount if this intercooler is used. You can see that it has some dirt, oil, and numerous bent fins. Christian from Modern Garage suggested using Calcium, Lime, and Rust (CLR) to clean it and then bend all the fins back. The fins are very small and of such thin material that it will take a number of hours to correct.

My IC didn't come with the factory turbo->IC pipe, but I made some arrangements to receive one. A special thanks to RyanC and Rallispec for helping me get that. If the factory piping does not work, then the existing IC inlet must be blocked off and a new one welded in. Here are a couple pics of RyanC's custom Rallispec installed WRX IC, but keep in mind that he is using a Minnam turbo kit and his turbo is mounted much lower than our turbo install:

Some people have also had some good luck with some used Saab intercoolers. They are much easier to locate and are probably cheaper too. They do require a little more elegant piping configuration, but it will get the job done. The intercooler is from a 1986 Saab turbo (not sure of the model name). Here is a pic of scootr's install:

Intake Plumbing -- In the case of the MY00, you will need to use a cone filter, or locate a pre-MY00 airbox. The reason for this is because the airbox containing the filter for the MY00 is replaced for an intercooler. I think all other model years can use their stock airbox with a little modification. RS'ted (I-Club) describes his airbox setup: "The airbox is from a '97 Imp - mine is a '00, so I bought this older style one from a local junkyard. To adapt it, I used a exhaust header reducer passed through from the inside. It's secured using the factory nut/strap thingies that typically fasten the MAF adaptor to the airbox. Sealed it with silicone - works great. The other piece you mentioned is a straight section of exhaust tubing that I welded nipples on for the breathers to connect to. I'm going to make a catch tank soon and re-route the breathers to that. As for the silicone tubing- the piece from the air box is 90 deg 2-1/2", the one on the compressor outlet is a 90 deg 2-1'4" in the photo. It has since been changed ( I added an intercooler) to a 135 deg 2-1/4". As for how I mated a 2-1/4 hose to a 1.7" turbo outlet, lets just say I improvised I slipped a short piece of 1-3/4" over the outlet to act as a "bushing", then clamped the 2-1/4" over that. I could have used a smaller diameter elbow, but given the angle involved I figured the larger piece would offer less impediment to the airflow. The connection, while less than elegant, hasn't given me any problem yet, close to 10k miles now."

When you buy the legacy turbo, chances are you will receive a 90 deg flange that bolts up to the turbo and another 90 deg plastic intake pipe. I plan on using this 90 deg intake pipe and extending it a little for the filter. The cool part about using this elbow is that it already has a number of inlets for you PCV vents. You can see my basic idea in this picture below. This is Blaster88's engine compartment.

Blow-Off Valve -- HKS SS, Blitz DD (left), or Greddy TRUST Type S (right) are preferred the most. I will probably be going with a Blitz eventually. Cost will be about $200. The BOV will be mounted on the turbo->intercooler pipe. If your car is a MY98 or MY99, you will actually need a bypass valve, which is capable of venting back into your intake tract. This is required for your car (MY98-99) to run properly. The MY00+ can vent to atmosphere or back into your intake tract, whichever you choose. Due to cost, I will just pick up an OEM Porsche part for now. This is a plastic Bosch BOV (middle), part # 993-110-337-50 and can be picked up from any Porsche parts dealer for about $33. Here is a sound file of what the bosch BOV will sound like (its on a Porsche, but hey, they have a boxer engine too, right?)

Rising Rate Fuel Pressure Regulator -- Either the Vortech SFMU, Bell Eng. 20007, Vortech FMU (non-adj.) or any other non-adjustable RRFPR. The SFMU and most of the Bell Eng. uits are fully adjustable. Cost will be anywhere from $150-$270. The Bell Eng. part is actually adjustible through the use of screws, but the Vortech unit must have disks swapped out to change the ratio. The stock MY00+ ECU runs a very aggressive timing map, so the more control over your fuel, the better. The RRFPR is needed to increase the fuel pressure based upon boost. Basically, for every 1psi of boost, it will increase your fuel pressure by 6psi (varies upon RRFPR or adjustment). The non-adj. RRFPR seems to run best at 4:1 with high baseline fuel pressure, or 6:1 with stock baseline fuel pressure. This will force more fuel in on each injector pulse. This is a way to force an NA ECU to run a turbo car. If you purchase the non-adj. FMU, you can also purchase additional rate disks for it from Vortech. This allows the exact control of the rate, without paying extra for the baseline fuel pressure adjustment. The fully adjustible units can be substituted as a primary FPR. This removes the need to purchase a seperate, adjustible, primary FPR to drop the fuel pressures after the installation of a high-flow fuel pump.

High-flow Fuel pump -- The stock fuel pump isn't able to sustain the high flows needed for forced induction. Stock fuel pressure at idle is 37psi and at WOT it is 47psi, with my fuel pump installed, the fuel pressure at idle went up to 48psi and at WOT it is 50psi. A fuel pressure regulator capable of adjusting stock idle pressure back down to stock levels is recommended. My preference is the Walbro 255lph pump sold by Vishnu. You may also see if you can source a Legacy turbo, Wrx, Supra, or Rx7 fuel pump for cheaper. I purchased my WAL255hpm fuel pump from JD's Performance for $99. Please keep in mind that the Vishnu Walbro pump is a direct replacement part, however the JD's Performance Walbro has a slightly different pickup. Be aware of the different flow/pressures the pumps are capable of. Here is a comparison of the Walbro and the stock (Walbro on the left), as well as the completed assembly with the Walbro installed:

EGT Gauge and Probe -- This is your main tuning device. A good temperature goal is about 1400 deg F. If you start to run higher than that, it indicates you are running lean. If you run lower than that you are ok, but it does tell you that you may be running rich. I had the probe fitting tapped about 2-3" from cylinder # 3 (passenger side closest to firewall) in the exhaust manifold. Cylinders are labeled on the top of the block where the plug wires go into the distribution block. Cost was $184 though Carparts.com with a coupon. I used an Autometer EGT Probe 3/16" 10ft NPT (racing) and Exhaust Gas Temp 0-1600F 2 1/16", Phantom. Part number for the probe is 5244 and the EGT guage is 5765. You may also want to source an AFR gauge so you can check your Air/Fuel Ratio as well. Most people say that an AFR gauge is worthless by itself, but when combined with an EGT gauge, you have a very powerful tuning tool.

Boost gauge -- Anything that will tell you how much psi of fun you are getting. Cost is about $50 from any Autometer dealer. I used an Autometer 2 1/16" Boost 0-30psi, Phantom. Part number is 5703. You can tap your boost gauge from any vacuum line except the map sensor signal line. I have teed the FPR line to my RRFPR and also sourced my boost signal line from there.

Fuel pressure gauge -- This will allow you to make sure your fuel system is functioning properly. Internal electronic is perferred. The range must be from ~30psi up to about 100psi. The full sweep version is $179 at Summit Racing; part number 5763.This is the Autometer 2 1/16" Fuel Pressure 0-100psi Phantom, full sweep. Or Autometer has a another version that is only $79.95 at Summit Racing. Part number 5709. This one is Autometer 2 1/16" Fuel Pressure 0-100psi Phantom,short sweep. It is a cheaper alternative, but it is not a full-sweep gauge, has less electronics, and is not nearly as accurate. I went ahead and purchased the short sweep gauge and I am left guessing the exact fuel pressure, but I get the basic idea.

Dual gauge pod -- Not needed, but it is a good way to hold your gauges. Cost is $24.95 from any Autometer dealer. Part number is 20590. I have my boost and EGT gauges in here.

Apex'i S-AFC, Split Second FCC1, or the Field Hyper R -- These devices allow you to enrichen or lean out your air/fuel mixture based on load and rpm. In a nutshell, these devices just modify the input voltage from the MAF or MAP sensor and gives the ECU a different voltage; thus tricking it into adding or removing fuel. If you have a MY99 or MY98, then it will work fine. If you have a MY00+ then you cannot use any of these for fuel enrichment once you hit boost. Because the MAP sensor reaches its max voltage output at atmospheric pressure and wide open throttle (WOT), any increases in the voltage caused by any of these devices will force the ECU into fuel cut mode. You may also run into the MY00+ ECU compensating for the AFC changes and negating all changes by varying the ECU operation. The best way (which is what I will be doing) is to go with the Tec-II or some other stand-alone engine-management. It is entirely possible to run the car with a variety of piggy-back electronics including a RRFPR, JCS Torque Chip II (or voltage clamp), J&S Knock Sensor, and possibly uprated injectors and air/fuel computer.

MAP Signal Voltage Clamp: ASR Check valve, J&S Electronics FCD, Split Second VC1, or Torque Chip II -- This is copied from an I-Club post by Rallispec. "The MAP sensor sends a voltage to the ECU ranging from .4 to 4.8V depending on the pressure. If the sensor sees more pressure than it was designed to handle (aka boost), it tries to send the ECU a signal that is out of range, thus causing the car to buck and hesitate. By installing a $ .10 zener diode to the ECU, you can now limit the maximum signal the ECU will see." Any one of those listed above will correct the boost problem for a MY00+ in one way or another. None of these are needed for the MY99 and MY98 Imprezas. ASR sells a MAP sensor relocation kit that allows the use of a check valve which will bleed anything above atmospheric pressure. The FCD has adjustible pots to achieve the exact voltage required and can be purchased from any J&S dealer; Trey Cobb and Christian recommend this. The Split Second unit can be purchased from Split Second. The Torque Chip II can be purchased from JC Sports. Prices vary from $0.10 to $120. All have been used successfully.

Zener diode -- Here is more information regarding how to use a zener diode to limit the MAP signal. This is copied from an I-Club post by Rallispec. " Under 4.7 Volts, the diode does nothing to the MAP signal, allowing the car to run totally normal off of boost. The moment the MAP sends more the 4.7 V, the diode bleeds it off thru its ground and limits the signal at 4.7 V. Ideally, a 4.8V diode would be best as it would allow for a little more injector duty cycle, but we haven't found any yet... Everything is done inside the ECU. Solder the Cathode end (with the stripe) to Pin #5 on ECU plug B136 ( it goes to a Pink with blue wire on the harness). Fortunately, the pin that needs to be soldered to is on top. On the other end of the diode, solder a small piece of fine gauge wire with a small ring terminal on the other end. Ground the ring terminal under one of the ECU case mount screws. You should cover any exposed leads with some insulation. Be careful when working on your ECU and do so at your own risk( disclaimer)...With only a 80 psi pump and a FPR, this diode setup seems to work up to 6 psi boost." After ordering 10 of the diodes from Radio Shack , I found out that the 4.7v 1W version is actually too much and clamps the voltage too early. Blaster88 says that a 1 watt, 5.6 volt version clamps right at 4.72 volts, part number 1N4734A. This solution should work, but has been found to create a transient lean spot on throttle tip-in. This occurs because of voltage bleed and is common among zener diodes.

Torque Chip II -- This is a "black box" which you wire into your ECU. It is supposed to contain logic that enhances your fuel curve, increases the ECU optimization, modifies your ignition curve, and removes the MAP boost problem. It can be purchased from IWTU Electronics . Here are comments from Larry:

"It increases fuel delivery for modified cars in a variety of ways, but also is supposed to benefit unmodified cars. I don't understand how it works (electrical engineering is a puzzle to me), but have been told what it does. It is very clever.

(1) First it enriches about 6% across the board but can lean out when needed, works with any year model (manual or auto tranny), and allows the ECU to train faster for the best air/fuel and acceleration (about 1 week for best results, but still helps right away).
(2) It has two possible outputs/wires for fooling the ECU into thinking the engine is approx 5% or 10% colder (depends on which wire), so it will enrichen more or less dependent on engine temps.
(3) It follows the car's acceleration (rpm vs time) and adjusts the air/fuel mixture for optimal acceleration like when the engine is free reving. This like a built in road dyno maybe? It helps the ECU remember these fuel requirements for future use.
(4) It watches the ignition timing and prevents the timing retard caused by the ECU when experiencing back-to-back full acceleration runs.

It definitely works better with my MY00 turbo than when I had an AFC. I still had to tune the fuel pressure for different amounts of boost, but the car at 5 psi and an untrained ECU with TCII (with and without using the electronic boost controller) was faster than when I had played with the AFC settings for three months! "

Check valve -- I have heard rumors that you will need to purchase a small check valve to prevent the charcoal canister from receiving positive pressure. You should have a vacuum diagram shown under your hood. Follow it until you locate the line going towards the charcoal canister and then add this check valve to it so it will not receive positive pressure from the intake manifold. This check vavle is documented in the JC Sports IHI Turbo Kit Installation Instructions and it goes in the vacuum line which taps off the top of the manifold and drops over to the passenger side of the throttle body. Some people say it is needed on all cars except the MY00+ RS.

Cruise Control -- In order to place a turbo inside the 2.5RS engine compartment, the cruise control must be removed or relocated. The cruise is a green drum-looking piece just in front of the passenger side firewall. It attaches to the strut tower with a metal bracket right alongside the AC Dryer. There are three bolts which must be removed in order to relocate the cruise. Once they are undone, you must also unplug the wiring harness. I have just removed my cruise for now, so the wiring harness was left dangling, the cruise throttle cable was removed, and the vacuum line was blocked. This vacuum line is ideal for tapping your boost gauge into. Please refer to the JC Sports IHI Turbo Kit Installation Instructions for a more detailed explanation.

Dan E. used a rather unique location for reinstalling his cruise. Most likely, I will follow in his footsteps. I do not know the details of the installation in this location, but I will be sure to document when I try it.

Engine Management

Split Second adjust. MAP sensor -- This is a unique device that is rather new to the market. It allows fuel to be tweaked by altering the signal being issued by the MAP sensor. I do not have much information on this so you do good to seach on I-club.com .

SDBC additional injctor controller -- Larry has had great results with adding in an additional injector just in front of his throttle body. Many will argue against this, but he has had wonderful results with this resulting in a 13.4 second 1/4 mile time at 6,000 feet. Again, a search on I-club.com will yield the best information.

Vishnu Tec-II (III) -- Complete engine management will eliminate the need for the RRFPR and map sensor manipulation. Cost is $2500 from Shiv at Vishnu Performance Systems. It will include the Electromotive Tec-II, Wintec Software, 550cc R/C injectors, and a boost control module. Compatible with all 2.5RS model years (slight additional costs for the MY98). This will be installed as a Parallel Engine Management System and will only take over the functions of ignition and fueling; leaving the rest of the duties up to the stock ECU. Installation time is usually about one weekend with many long hours of tuning to follow. However, Shiv does provide a baseline map to drive your car around and many people have simply bypassed initial tuning for awhile. Contrary to many beliefs, a PEMS system doesn't require the laptop to be in the car at all times nor does it require constant tuning. There are many people whom have achieved a state of proper tune and have not had their laptops in their car for months. Tune into Richard Diamond's Tec-II FAQ here for more details. You can find the installation instructions here.

Unichip -- Trey Cobb has had some decent results with using the Unichip to tune the RS-T's. There is atleast one person on the I-club.com that has gone this route. It's not very popular and I am not sure on the exact details after having talked with Trey about it.

Let me know if you need any information, or have any revisions to what I have posted. Email link is at the bottom of the page.

-Jon