Subachad 1993 Impreza 1.8 Liter Turbo Build Up – Original Article

This is the original article from when I built up my original kit in 1999.

Disclaimer: This article is written for information purposes only. In no way do I suggest doing this. If you do… this information should be interpreted as a tool or learning device, not a “how to.” I take no responsibility for what you do on your time. That being said, this information is correct to the best of my knowledge.


After seeing turbo cars pop up in magazines and after owning a 1990 Eagle Talon TSI Turbo, I decided to look into turbo charging the Impreza even more. Once Minnam Racing came out with a turbo kit for the Impreza, I realized that it is possible to feasibly turbocharge an Impreza. At this time the thought of 4 spinning tires, neck-break acceleration, and the quarter mile times of a Porche 911 turbo were mostly just fantasy. Soon after however, something pushed me over the edge. The March 1999 turbo magazine. On page 130 lies Byron’s now 500+ horsepower daily driver Impreza.

With an “if they can do it, we can do it” attitude a friend and I started looking into turbos. The first project was a 1990 Toyota Tercel. A Garret T3 was sourced from a retired Turbo Thunderbird, and soon mounted up. It worked, though maybe a little too well. Tercel’s don’t seem to like 15 pounds of boost and that was that.


If you are reading this and considering actually building your own kit, I recommend you do some research on your own. Most of my knowledge was gained from,, JC Sports (which is now out of business), Turbo magazine, and doing lots of Internet searches for turbo cars. Research at the time was a bit sketchy given the amount of time aftermarket turbo Impreza’s roamed the streets. The small consensus was 5 pounds without an intercooler or any other electronics and 7 pounds with an intercooler and fuel and timing management. According to JC Sports, their front wheel drive 1.8L Impreza went from 83hp at the wheels to 142hp with only 5 pounds of boost, no electronics and no intercooler.


This made the page too large, so check out the 93 Impreza “Simba” Initial Turbo Parts page for more info on the parts used.


The first place I looked was to look at the different turbo’s and compressor maps. The compressor maps are somewhat cryptic to read, but they basically let you know what size turbo components you need for different engine sizes. After getting hyped up about a Turbonetics T03/T04 hybrid with a ceramic ball bearing center, I went over to to check on price, about $1300 for the turbo and $220 for the wastegate. Too much for me… time for a new plan. My friend with the turbo Tercel was able to get a T3 off a Thunderbird for $45. I however couldn’t find one. What I did find were numerous Subaru turbos. Total search time lasted about 3 weeks. Once I found one in good shape, I was able to pull the turbo with wastegate, up pipe, and downpipe in about 45 minutes. Would have been quicker, but the junkyard wouldn’t let me take the pre cat, so I had to cut it off with a dull hacksaw. One modification was needed for the turbo to make it work. It comes with a 1½ outer diameter outlet flange which is too small. Good luck finding a 1½” to 2” reducer. I had the outlet part of the turbo machined to a 2” outer diameter so I could actually get a silicone hump hose on it, problem solved and they also bored out the actual port for me as well. (thanks S&H Racing in Beaverton Oregon) They have done a lot of machine work for my friends and I, always great work, good turnaround time and they are nice too which is important to me, especially with my strange requests. One place actually said “no one modifies Subarus” and laughed at me. This was for some custom suspension work and new bushings, needless to say, I never returned.


Oil Feed/Return:

This should have been easy. I knew how much steel braided line I needed to get from the turbo to the oil pressure sending unit. I also knew I’d only need about two feet to return to the pan. To the pan was easy, I had a fitting welded to the pan and just ran a two foot #12 11/16” steel braided line. I used silicone to help seal the top and A/N fittings to hold it on to the Oil Pan. For the Feed, I used #4 7/32” 3’ steel braided line and the necessary fittings for the turbo and oil pressure sending unit. The unit pictured below with the A/N fittings on it is actually from ISR. For the feed, go through ISR. The line is about $40 and already has the fittings mounted to it. It also takes the oil from right below the throttle body as opposed to the oil pressure sending unit.

For the oil return, you should be able to get a fitting that returns the oil directly into the head on a 2.5, but not for the 1.8L. Just use an A/N fitting at the head and slip the other end over the turbo or an A/N fitting there depending on preference.


2¼ high flow cat and muffler:

I used a Dynomax muffler (28-2371) and a 2¼ cat that is actually for a Chrysler turbo, but I lost that receipt so I really don’t know the part number for the catalytic converter. All of my exhaust work was done locally at a muffler shop. It really helps to know someone here, otherwise they might not be too willing to work with you. Another tip is to go to a shop that does a lot of custom work. The shop I had it done at is really into building muscle cars for drag racing, so they appreciate what I am doing. I would leave the name and shop, but it’s under new management now.

Here’s a picture of the old up and down pipe that came off the car. Prime example of how NOT to do it, notice the crush bends and overly bad design.


UPDATE: That exhaust is off. I made a custom 2″ up pipe, 2.5″ down pipe and all the way back with a 2.5″ exhaust.


A few years ago, I drove a turbo wagon and seem to remember it having about 5 to 7 pounds of boost. Armed with this information, I left the stock wastegate on the turbo. The very first drive I watched the needle shoot up to 10 pounds. WOW, not much lag, but too much boost. Get a Turbonetics or Tial 3-5 pound wastegate. Other turbo owners are complaining about the Deltagate by Turbonetics, saying they are getting boost spikes due to a “sticky” spring. That said, the TIAL might be a better option. Even if you want more boost, because you can always turn it up, but you can not turn it down. More information is available in the FAQ section under wastegate. I was able to get a good deal on a Deltagate, so this is what’s going into my install.

UPDATE: The current setup uses no external wastegate. With the TD04L on my 2.2/1.8 hybrid, I peak at 7psi.


This was the most expensive part of my whole setup. I have a Weapon-R intake that goes to the turbo. From there is a 2” hump hose to the 2” exhaust tubing, to a 45’ silicone elbow, to more exhaust tubing, to a 90’ silicone connector, to more exhaust tubing, to a silicone 2” to 2.75” transition into the throttle body. The silicone connectors were purchased from and cost about $210 with shipping. Actually it cost me $295 for the connectors, but I had 2 extras. If you are using a Weapon-R intake, it is important to get the Air Filter mount from Kartboy Kustoms as the “universal” MAF mount that comes with the intake is more comical than practical.

RE: Silicone connectors needed for intake, Joel wrote me this:


UPDATE: The intake charge pipe has been replaced with all mandrel bent tubing and Silicone connectors from Belair Composites.

The turbo to MAF is still in process.

Boost Gauge:

Quite possibly one of the most fun parts to having a turbo. The first time you see positive pressure, you’ll smile. This is the first part that should be put on the car, even if you don’t have a turbo. It lets you know how your car is running. Also without it, I would have no way of knowing I was getting 10 pounds of boost. The boost gauge I have is an Autometer 2” (P/N 5703) boost gauge and a mounting cup (P/N 2204) as well. Now that Autometer makes pillar mounts for Imprezas, I’d much rather go that route.


Blow off Valve:

For the blow of valve (BOV), I used a Bosch from Turbonetics. Basically drill a hole in the intake and stick a Home Depot 1″ O/D pipe on there, plug a 1″ heater or dishwashing hose in, then connect the hose to the BOV. The Bosch is plastic so you can’t weld it on like you can a more expensive one. The Bosch BOV is also only $40 so it was the BOV of choice for my initial build up. The air from the BOV is then returned to the filter side of the Intake via hose, but on the turbo side of the MAF so as not to confuse the computer. With the BOV unhooked, it makes a nice loud PSHHHHH sound when letting up the gas, but the car doesn’t idle very well, in fact it usually just dies and is hard to start. The BOV is not absolutely necessary, but I recommend it, read the FAQ on how it works for a better explanation.


Just putting an Intake and exhaust on a car can cause it to run lean. That said, something has to be done about the fuel and every car is a little different, so the settings will differ by car. A more powerful fuel pump is in order to supply fuel. I have a pump from an Rx7 twin turbo for mine. A Rising Rate Fuel Pressure Regulator (RRFPR) is needed to increase the fuel pressure. The car will run “ok” at 5 pounds with no fuel mods, but you will be running lean. For the RRFPR, most people use a 4:1 which means for every one pound of boost, the fuel pressure is increased by 4 pounds. Dyno testing is really needed to get a better setting. 92 octane is also necessary as it is slower burning and less prone to detonation. I would STRONGLY recommend engine management, but if you can’t do it please don’t go cheap on the fueling. At least get an SAFC. The RRFPR is somewhat of a “patch” job and is simply not enough.


If you are even considering this, I recommend more research. Read turbo magazine, check out other sites with turbo cars such as Jon’s. Don’t limit yourself to Subarus, some of my research is from turbo Civics. One other point I would like to mention is the fun factor of owning a turbo. The whine is great, the blow off, spinning all 4 tires, and smack talking mustang GT’s. That is about it. Thanks for reading this through, I hope it helps. If you have any further questions, comments, or just want to chat, be sure to check out the FAQ, or email me.