The car we built is a 2013 Impreza WRX STI sedan. It had already been to us for a stage 2+ parts install and flex-fuel tune previously, so the car did have some parts on it already. However, with a goal of 600 wheel horsepower, basically every system would need to be touched or upgraded in some way. We needed to address the engine, clutch, fuel system, cooling , oiling, etc. This is no small task in itself, but to also make everything fit together, play together nicely, and look good, is where the good builds are separated from the bad builds. We set out to make this car perform up to the clients expectations, be a streetable/drivable car without issues, and look good when the hood is popped. This is how we did it.
The heart of this build is the engine. The block needs to be able to handle considerable forces including over 30psi from the oversized turbocharger. We opted for a closed deck EJ257 STI block, that was bored and honed for 99.75mm JE pistons. The block was drilled for 1/2" head studs, which will allow for more clamping force to keep all that boost contained and the heads where they need to be - attached to the block. We planned on using ARP case bolts to keep the halves of the block bolted together as tight as possible, so the block was torqued down to ARP specs and line honed to ensure the mains would be perfectly aligned for our crankshaft and bearings. Lastly we had the mains pinned, one more step to ensure that the block locks together tightly and will not shift under high loads. When your block starts to shift and move around bad things happen. Explosive things. So keeping everything together for a high horsepower build like this was imperative. We also had the rotating assembly dynamically balanced. This is done to prevent unwanted vibrations when the engine is run at speed. Vibrations can slowly (or quickly if bad enough) rattle an engine to death, we don't want that to happen.
Once we received the upgraded block halves back to our facility we set about cleaning and assembling the shortlblock components. The crank, pistons, rods, and wrist pins were all measured and inspected. Our builder then hand polished the new STI heat treated crank to a mirror finish. The wrist pins, piston pin bores, and big rod end bores were also hand polished. Polishing the rotating assembly takes away minor surface imperfections that can catch on other components or inhibit oil flow. Once we were satisfied that everything was weighed, measured, polished and cleaned to our standards we set about assembling the block. In went the polished crank with new King bearings. Manley Turbo Tuff I-beam rods were used in conjunction with JE FSR pistons, which were all matched to within 1 gram of each other. ARP case bolts hold the block together tighter than the OEM bolts, and we topped off the crank with a Fluidampr pulley. These pulleys actually help to absorb unwanted vibrations and have been proven to increase horsepower through lost energy. It's win-win with improved engine life and more power!
With the block ready for power we moved on to the heads. Kelford stage 2 cams were chosen as our bumpsticks to keep the turbo fed with enough exhaust gasses to churn out 600 angry horses. These were backed up with Kelford race springs and titanium retainers. New manganese bronze intake and exhaust valve guides were installed and a performance valve job was performed. Brand new valve buckets were used, as re-using old buckets with new cams can result in uneven wear, which will eventually destroy the valvetrain. We also spent time working the camshafts to make sure oiling was adequate for the face of the buckets. Subarus are known to eat buckets/camshafts, and doing things right at this stage in the build can prevent a very costly failure later on. Once the heads were assembled, valve clearances were checked and set and the heads were ready to be bolted to our block. We used JE Pro-seal headgaskets along with a special sealant we like to get a really good seal around the entire face of the gasket. 1/2" Head studs were then torqued down in series to clamp the entire assembly together. The longblock was now ready for the extra goodness.
Oiling upgrades included the Killer B Ultimate oil pickup and baffle, to keep precious oil flowing from the pan into the engine. We inspected and modified an OEM oil pump next. The gerotors are inspected and polished, the inlet and outlet bores deburred and polished, and the bypass piston and bore is deburred and polished. This is done to ensure oil can move freely through the pump without restrictions, and that the bypass does not get stuck. We have personally seen a bypass get stuck and destroy an engine, so this step is very important in any engine build. We then closed the pump with loc-tite, as the backing plate screws are known to back out with heat and vibration. The oil pump was now ready to go and was bolted in place. An OEM water pump, pulleys, and oil pressure switch were used. Upgraded and cleaned AVCS gears and a performance timing belt were then installed. The bottom of the engine received solid Cusco engine mounts, and then we set about the intake side assembly.
The STI intake manifold was bolted on with billet IAG TGV deletes on top of 8mm phenolic spacers. The spacers will help keep unwanted engine heat from transferring into the intake manifold and increasing charge temps, and the deletes provide a smooth transition into the heads for more power. Radium fuel rails were then used with 1700CC ID injectors. We ran our own fuel lines using PTFE fuel line and an fittings. PTFE hose is ideal for use with upgraded fuel system as it can withstand harsh E85 fuels and it prevents unwanted gas fumes from permeating through the hose. We added an AEM 5 bar MAP sensor to give us the headroom we wanted to tune this setup. IAG air pump delete plates were used to get rid of the worthless OEM air pump, which saves space and about 12 pounds of weight. It was now time to drop the engine in, and get started plumbing in fuel, mounting the turbo, and making it all fit.
The turbo, usually the star of the show, was specced for the power numbers our client asked for. Instead of just bolting on the biggest turbo we could find, we researched what would provide the power numbers we wanted, without the side effect of a ton of lag. A properly sized turbo is imperative to preserve the drivability of a car and a usable powerband. Our chosen turbo was a Borg Warner EFR 83/74 1.05 A/R T4 Twin Scroll unit. We would be using this with twin external wastegates. This was going to be a badass setup and we couldn't wait to hear it scream. A Full-Race manifold, up-pipe, and downpipe were used to mount the turbo in the STI. The piping was beautifully finished in a satin black ceramic coating, which helps keep the heat inside the pipes. This promotes faster exhaust gas flow and helps to keep the radiant heat down in the engine bay, which is very important in a tight engine bay like this one. We bolted the header to the heads using ARP studs and nuts, we did this because the header assembly weighs quite a bit, and the upgraded hardware will help to keep it in place through tons of heat cycles. Twin 38mm Tial wastegates were mounted with downtubes and we moved on to the tedious stuff!
Space is at a premium in an STI engine bay, and making a massive turbo like this one fit was not easy. We started by re-routing the main engine harness to the backside of the shock tower. The next major item to move was the ABS module. We cut the original bracket, very carefully re-located the ABS module and hard lines up higher on the shock tower, and then re-welded the bracket and secured it all in place. The next item to make a move was the EBCS, a custom bracket was made and it was mounted below the turbo, to make room for the huge intake that would soon occupy that space. One of the last major items to be moved was the coolant reservoir. This needs to be the highest point in the cooling system to allow for proper bleeding of the coolant system once filled. The reservoir was relocated into the front of the intake manifold with a custom bracket, and new lines were run. While we were in that area a new power steering line was run under the intake manifold. We used an AN fitting and SS line for this. The original PS line ran too close to the turbo, and this can end in a fire...not what you want at all. One last item that needed a new home was the IAG competition AOS. It would normally sit where the new turbo lives, so we made a very nice custom mounting arm that would allow us to mount the AOS next to the pitch stop on the driver side. Some custom lines and a downtube and the AOS was ready for action.
We then moved on to the fuel system. We were going to need to move a lot of fuel from the tank to the engine when using E85 at full tilt. So we started by installing a Radium in tank hanger and hard-wiring in a Walbro 450lph pump. The stock fuel lines were going to be too small for the fuel we wanted to move for this tune, and for more potential power later, so we ran all new large diameter PTFE fuel hose from the tank to the front of the car, and back for the return. This was secured along the chassis with rubber grip mounts and careful routing to keep debris and road hazards away. With space at a premium in the engine bay we mounted our in-line fuel filter to the driver side firewall with a custom mount. Next to that we mounted a Cobb Flex-Fuel sensor with another custom mount. They are tucked into a safe place, away from heat and road debris, we were happy with the placement and how clean it looked. Next in line was a Radium FPR and gauge, so we can monitor and adjust fuel pressure. Custom fuel lines were then run to the rails and back to the tank. A few spots were very close to the turbo, so they were wrapped in gold tape to reflect heat away and keep the fuel as cool as possible. Fuel system done, we moved on to the intercooler.
This STI already had a Mishimoto intercooler installed, so we kept the core at the clients' request, and set about making new intercooler pipes to work with the turbo setup. We used a combination of 2.75" and 2.5" pipes to route the intercooler tubes in the most efficient path possible with the given space. Once welded up and situated where we needed them we painted the piping wrinkle black to complete the finished look we were going for. The Tial BOV was mounted close to the turbo to vent excess pressure when needed. The turbo was clocked for the most efficient feeding and draining of oil and to give us the right angle for the outlet tube. We finished up the piping with a custom 4" intake to feed the beast. It fit perfectly in the space we had created by moving the ABS module and other components earlier in the build.
Click the link below to jump over to "Part 2" of this build, and the completion of this beast!
Part 2 - http://www.circuitmotorsports-blog.com/2017/07/600hp-built-and-tuned-sti-all-sauce_11.html
-Circuit Motorsports is a performance tuning shop located in Orlando, FL. We have a professional tuner on staff who is a certified Ecutek Master Tuner and a Cobb Protuner. Our shop specializes in import performance cars from Subaru, Nissan, Mitsubishi and more.
Facebook - www.facebook.com/circuitmotorsports
Website - www.circuitmotorsports.net
Youtube - www.youtube.com/circuitmotorsports
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