Sam's 2005 Subaru Impreza WRX STI

 Introduction:

Disclaimer: I am an engineer, not a professional mechanic, or a car dealer, or a shop owner. Modification of any of your car's systems carries with it risks that may include loss of warranty, failure to meet emissions regulations, and failure of the system itself. You pay to play, make your own decisions and take responsibility for your own actions.
 Side Note: Your manufacturer is entitled to void any warranty can prove was caused by an altered or non factory component. If you put a bigger turbo on your car and the engine blows up with 3000 miles on it, or your transmission grenades, or your clutch catches fire, good luck getting it replaced under warranty. On the other hand, if your window won't go down any more and they want to void your warranty because your engine is modded, you can take them to court.

 By far the number one question I got when talking about my car was "Why didn't you just buy an STI?". Granted, the Subaru Impreza STI was everything my 2.5RS was meant to be: Turbocharged, aggressive looks, aggressively tuned to handle and stop like a race car. Still, the question never failed to annoy: My 2.5RS was a 6 year old car when the first STI came to the United States, and it had cost me $11,500 off an Ebay Auction, whereas a new STI retails somewhere around 33thousand dollars. My usual response was something sarcastic along the lines of: "Yeah, I was kind of torn between the Lamborghini Murcielago and the Buggati Veyron, since I wanted all wheel drive, but then I realized I had no money and bought what I could afford".
 The trouble is, between all the extensive modifications I performed to my RS in order to make it accelerate, stop, handle, and look the way I wanted it to, I had spent as much money as what an STI would have cost. Worse still: My RS had a habit of breaking really expensive parts at somewhat regular intervals (3 engine blocks, 2 transmissions, wheel bearings, half shafts, etc). This was fantastically inconvenient and frustrating, because not only was the car costing me a small fortune, but it was also my only car and my daily driver, so part failures routinely meant lost classes, having to hitch rides, walk 2 miles each way to school, etc etc... Nonetheless, I justified my investment with the simple fact that the RS was not an STI: no, it weighted over 400 pounds less, and it put more power down at the wheels than a new STI makes at the crank. Simply put, for the money, my 2.5RS was unbeatable; nothing I could possibly buy would even come close to it when it came to thrilling every time the gas pedal was put down. And it wasn't just a straight line car either; the RS had virtually every single braking and handling upgrade available.
 

 Then, within one and a half months my clutch went (It was a SPEC clutch. It lasted approximately 6 months of non aggressive street driving. Side note: SPEC; makes hands down the most poorly built clutches on the market today). Thanks to Spec's wonderful consumer support I was convinced to replace my flywheel, clutch master cylinder, and clutch slave cylinder; items I did not need.
 Then my power steering pump went. Then a wheel bearing. Then my Oxygen sensor. In 1 and a half months I drove the car for approximately 5 days, but spent over $3000 in repairs. That was it; with the RS still in the shop I went on Ebay and bought the one car -the only car- that could substitute it for me... A Black, 2005 Subaru WRX STI, with tinted windows. It was a dream come true. Oh, and it already came with some of the upgrades I had on my RS (larger swaybars, chassis reinforcements).

 Driving the STI:

 Well, in three words, it was kind of slow... Granted, it will hook up and pull hard through the gears; triple digit speeds come with ease and it will definitely go as fast as anyone could possibly care to drive on any public road, but compared to the 8100RPM redline, 20pounds of boost, sub 2800lbs 2.5RS I had, the STI felt more like a heavy, hopped up 4 door sedan than a sportscar...
 BUT... What it gave up in acceleration, it made up everywhere else... The STI is quiet, smooth, has a really nice interior (well, compared to the RS anyways), and stops and handles like nothing else I have ever driven. Yes, on STOCK suspension (but upgraded swaybars) the STI can turn and brake better than the RS could ever hope to. What if I change a couple of things about the STI? Could I make it my ideal car?

 The Makings of a Sportscar.

 One thing always drove me crazy about factory vehicles; in an effort to quiet down drive train noise, manufacturers will mount the engine, transmission, differentials, shifter, etc all on soft rubber bushings. The pliable rubber absorbs vibrations and deadens noise that would otherwise rattle the chassis, but at the same time it will also create play, or "slop" on the driveline. This is obvious on any vehicle, but it is specially bad on all wheel drive cars, since these will have 4 halfshafts, 3 differentials, and a hinged driveshaft, all mounted on soft bushings. The net result is that when the gas pedal is pressed or released there is a slight time delay during which the entire driveline tenses up and compresses the bushings, or relaxes and bounces on its bushings for a bit when the gas is released. Rapid throttle transitions will make the entire car buck and bounce like it is powered by a giant rubber band. Most people don't seem to care, but I find it extremely annoying; when I hit the gas, I want the car to squat down and GO! NOW!
 Of course as with any modification, reducing or eliminating this will come at the compromise of added noise and vibration within the car. We begin by looking at race cars: These have no bushings; everything is a solid link or a Delrin (a type of fluoropolymer) cylinder. They will also vibrate fillings right out of your teeth, so that won't do for a street vehicle. How about a compromise?
 Subaru fortunately makes such a compromise; Group N homologated rally style Engine and Transmission bushings. These look identical to the factory parts but utilize a harder rubber compound; they still dampen vibrations, but at the same time will make the car more responsive. With the installed the difference was almost instantaneous. The engine pitch stop is also very soft and allows it to move back and forth during shifts. Replacing it for a billet aluminum unit eliminated that last bit of movement. This is something we have to be careful with though: a solid link between the engine and the firewall will resonate the entire chassis, making in-cabin noise unbearable. Fortunately Kartboy developed a pitch stop with polyurethane bushings that effectively locks the engine in place while at the same time not producing excessive cabin noise.

 Engine and transmission mounts aside, the rear differential is still mounted on what looks like recast gummy bears, and will make a nasty "THUMP!" on hard shifts. Not acceptable. Fortunately Turn In Concepts, a California Based Company, produces polyurethane bushings for just this purpose. These will tighten up the differential mounting to the chassis and eliminate its movement during hard shifts. Again the difference here was obvious; no rear differential movement and zero banging between shifts.

 Now we address the shifter: This isn't particularly what I would consider a "performance improvement", but the stock shifter on a stock STI has a long throw and is mounted, again, on the same stupid rubber bushings that make the rest of the driveline feel so disconnected. With the car in gear, the shifter can be moved side to side and back and forth by almost half an inch, and gear engagement feels vague and imprecise. The movement between gears is also quite large; to my liking, at least. The stock STI shifter is probably better than most other stock shifters, but, again, it can be improved.
 Kartboy Rear Shifter Stay Bushing
 Kartboy Shifter

 Power:

 Of course, you can also hear all that "free breathing", and, as a result, cars with altered intake and exhaust systems are always louder. Some times this can get downright obnoxious. I picked the quietest exhaust system I could find: A 3" twin tip Borla Hush catback. Borla backs their products by a million mile warranty and makes all their exhausts out of 304 stainless. They also sound the best out of all the exhausts, in my opinion (and, no, I haven't been paid to write this). To complete the exhaust mods the care came with a 3" bellmouth catted downpipe. I had it substituted for an Invidia 3" stainless steel, catted bellmouth downpipe. To reduce under hood temperatures and improve exhaust velocity I had the exhaust pipe first ceramic coated, then wrapped in Thermotec Gen2 header wrap. This combination has proved extremely successful; to the point where I can put my hand on the downpipe even after the engine has been running for a long time. My car also came with headers; these were GTSpec Generation 2; they are integrated with a high flow up pipe. The reasoning behind aftermarket headers is that by utilizing a lager pipe diameter they will be less restrictive at the higher power levels. A delayed merger between separate runners also helps keep exhaust velocity high and turbulence low. Finally, they are also a lot lighter than the factory cast iron pieces. This doesn't come without disadvantages however. For starters, the larger diameter tubing takes longer to fill up with exhaust gases, resulting in added turbo lag and reduced low end torque. Also, more importantly, the thinner wall tubing also loses more heat to the environment, and since exhaust gas heat is the energy that drives the turbocharger turbine, aftermarket headers routinely perform worse than factory units when it comes to low end torque and turbo spool. I intend to remedy these two issues by ceramic coating the headers and up pipe and wrapping them with Thermotec Gen 2 header wrap. We will see how this goes.

 For the intake my current modifications have been to saw off the intake air resonator on the fender well; this allows me to hear the turbocharger better from inside the car. Not a real performance modification, but it adds to my driving pleasure, and that's what this is all about, after all. I also installed a K&N Panel air filter.

 Engine Tuning:

 One of the great things about modern engine management is that the ECU will make the engine do whatever you tell it to do. A poor tuner will blow an engine in seconds, but a good one can squeeze spectacular amounts of power from an aggressively tuned motor; there are STIs in the states today making in excess of 600horsepower with a stock ECU. Some even running stock engine blocks!

 When it cames to engine tuning the options are 3:
1- A replacement ECU (Standalone): Standalone ECUs completely replace the stock unit and offer the greatest degree of tuning flexibility for the engine; things simply not possible with stock ECUs can now be done: staggered injectors? Dual fuel tanks running 2 different kinds of fuels? An engine never made for that car? Forced induction on a naturally aspirated engine? Antilag? Not a problem! However, these are also the most expensive tuning option, running over 1000 dollars for even a basic unit, and that's before tuning costs are thrown in. Also, standalones are tuned from scratch, and as a result commonly suffer cold start, idle, and part throttle drivability issues. Remember that the factory ECU has had a team of professionals dedicate days, weeks, maybe months fine tuning ALL aspects of engine operation. It is unrealistic to think one tuner is going to achieve the same level of sophistication on a standalone working over a couple of hours or days.

2- Piggyback computers: These intercept incoming or outgoing signals from the ECU and modify them with the intent of altering some engine running parameters; air fuel ratio, ignition timing, and boost are commonly dealt with by piggybacks, and these will typically leave the stock ECU alone to do its factory duty at low throttle inputs, resulting in factory-like driveability. Cost and retaining factory cold start, idle and part throttle are the advantages, but lacking in sophistication, piggybacks are limited in what they can do. Also, by "lying" to the engine or ECU, piggybacks can very often allow the engine to run itself in a destructive manner without any means for factory safety nets to proect it. A good example are boost controllers; Most factory ECUs have provisions for reducing boost under situations when the engine is at risk, such as excessive intake air temperatures, detonation, low octane level. With a piggyback or a standalone boost controller the ECU will try in vain to reduce boost, and then watch helpless as the engine destroys itself. Not good! Examples of piggybacks are Apexi S-AFC, Apexi ITC, Unichip, Utech. Some Piggybacks will pass computerized emissions tests.

3- ECU Reflashes: This is a recent innovation in the automotive world. Many of today's ECUs are as sophisticated or more sophisticated than many standalones, and through a reflash can be reprogrammed to accomodate modifications or simply to run the engine more agressively. Factory idle, cold start, part throttle driveability can all be retained, along with coded safety nets such as knock based ignition retard, intake air temperature variable boost and ignition timing, etc. Reflashes are also commonly the cheapest tuning option.
 There are currently 3 reflash options for Subaru ECUs; ECUTEK, Cobb's Accessport, and the free Enginuity software. Reflashes will typically pass emissions tests, and even when they can't the ECU can be converted back to stock with another reflash, and it is very difficult to detect that the ECU has ever been reprogrammed in the first place.
 

 For the reasons mentioned above I decided to go with an ECU reflash. I picked Cobb's Accessport for various reasons, namely the ability to reflash on the fly, and to store various programs including different octane levels, valet mode, etc. Finally, Cobb's promise of Launch Control and Flat Foot Shifting had me sold. (More on this later).
 The AP plugs into the car's OBD-2 port and with a 30 second flash will reprogram the car's ECU to run 17.5 pounds of boost, along with a more agressive map. Cobb claims the reprogram is good for 350HP, 385ft-lbs torque. Not bad! Now the STI is starting to feel like its got some balls...

 Brakes:

 Wheels, Tires, Handling:

 Instrumentation and Interior:

 2- Overboosting: A lose vacuum hose going to the wastegate actuator, a faulty wastegate, or wastegate control solenoid, improper tuning, or even a large change in atmospheric conditions for manual boost controller cars can cause a large spike in boost pressure (spiking) or a gradual uncontrolled rise in boost pressure (creep). Once either occurs the engine will either detonate, or the pressure will physically bend pushrods, blow head gaskets, destroy bearings, etc.

3- Detonation: Lean conditions caused by plugged injectors, faulty fuel pumps, faulty fuel pressure regulators, lose lines, leaking lines, overboosting, poor tuning, excessively advanced ignition timing, excessive in-cylinder temperatures, insufficient octane levels, are all examples of factors that will cause the air/fuel mixture inside the cylinder to ignite prematurely or detonate. Once this occurs bearings can be hammered apart, rods can bend or break, piston rings can shatter, piston crowns and/or cylinder walls can become pitted, and gaskets can be blown. Every detonation event carries with it a chance of irreparable engine damage. Large events or rapid succession of detonation events can catastrophically destroy an engine (literally blow it to pieces).

4- Excessively high combustion chamber temperatures: Caused by the same factors as detonation, and typically leading to detonation. Other factors contributing to excessive combustion chamber temperatures can be excessive engine load or excessive engine temperature. If detonation does not occur, other things can happen; the oil can overheat and shear too thin to adequately protect the engine, or the pistons can become so hot as to expand and seize into the cylinders.

 Sounds scary, doesn't it? I probably wouldn't know much of this if I hadn't experienced oil starvation on my first motor, blew a head gasket on the 2nd one, detonated a piston apart on the 3rd one, and overheated the 4rth one to destruction. As a result, I am now much more aware of how my car is running and much more cautious of engine operating parameters.
 Obviously, none of this is something you need to be worrying about on a stock vehicle, or on a trip to the grocery store. However, asking your factoy motor to pump out 50, 60, maybe 100+HP over what it was designed to do, and then tearing through the gears at wide open throttle for extended periods of time without any means to monitor what is happening is akin to playing russian roulette with your engine; some times you get lucky, some times you don't.
 Here is what I consider to be absolutely essential in any modified boosted motor:
1- Boost Gauge: Always. And watch it too.
2- Oil Pressure Gauge: A stock oiling system on stockish power levels in a relatively new car is probably OK without this. Otherwise watch it, specially on a track.
3- Exhaust Gas Temperatures: Useless unless a high quality, responsive one. It will let you know if ignition timing has been retarded due to knock or other factors, and will warn you if engine combustion chamber temperatures are becomming too high. I would never attempt a top speed run without one.
4- Air/Fuel Ratio: Expensive, but it will tell you at a glance about vacuum leaks, boost leaks, will help diagnose idle problems, will let you know if the tune is too agressive, if the engine is running too rich, too lean, etc. I consider it as important as a boost gauge, but many people only consider it necessary for tuning.
5- Knock indicator: I don't recall ever hearing knock, but I have had an engine literally detonate itself apart. Some engines simply do not knock audibly, or your car may be too loud for you to hear knock. Whichever is the case, I am currently expermenting with a Turbo XS Knocklite.

 Results:

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