Sam's Subaru STI

 The car I tried to build, but ended up buying:

 The Goal:

My fascination with the STI had always been  around its DCCD (Driver Controlled Center Differential) enabled 6-speed transmission. This is, in my mind, the best transmission you can have in any car that is not an exotic. I wanted a 2005 model because in it the front differential is a Haldex gear type unit. Also, the rear hubs are larger and stronger, the rims are wider, allowing the use of wider tires, and the interior has been improved over the 2004s. But back to the transmission:
 It has 3 limited slip differentials; the front is a gear type torque sensing unit (Torsen). The rear is a clutch type posi, and the center is a computer controlled electromagnetically actuated clutch pack that can vary the degreee of front to back power split dynamically. When set in automatic mode, the STI uses input data from a G sensor and a Yaw sensor to figure out if the car is braking, accelerating, or cornering, and then if in cornering it is under steering or over steering. It will then change the degree of slip on the center differential to achieve neutral handling. This results in a car that handles like nothing else I had ever driven up to then;  I could purposely throw the car into a corner at a much greater speed than it was capable of taking the corner at, knowing it would slide, then get on the throttle and let the computer and the transmission figure it out, clawing and sliding my way out of the corner with complete confidence. In launching, the full limited slip differential setup provided incredible traction, putting down full power in any gear, on virtually any road condition. Oh, and with the DCCD set for "full rear", it could do some incredible slides too!

 For me the STI 6 speed transmission, and all the uprated components that came with it (thicker halfshafts, stronger gears, larger differentials) alone was worth the cost of the STI. But it also had a MUCH better interior than my RS, much better seats, HID headlights with a dash mounted leveling switch, and massive Brembo brakes. In short, the STI was the complete package; power, handling, speed, comfort. It was the car I had always tried to build. And this time it would be reliable, because it was stock.

 The Car:

The Engine

 The engine on all US-Spec STIs is termed "EJ257". Unlike the 2.0L EJ207 from Japan, it displaces 2.5L, presumably in order to make equivalent power with the inferior fuels available here. On paper, the bigger engine looks great: More power and torque prior to the turbo spooling up, and more power and torque at any given boost level once the turbo does spool up. This engine also incorporates AVCS (Advanced Valve Control System); a system that retards camshaft timing on the intake side to further reduce turbo lag, then advances it for optimal power on boost. The same system keeps cam timing fully retarded on cruise, so as to reduce pumping losses and net better fuel economy.

 In practice, the engine had two major letdowns for me: First of all while it may in fact have spooled up faster, it never felt that way because the car was so heavy. Secondly, it redlined at only 7000RPM, and started to lose power well before that. The low redline coupled with short gearing made for a lot of shifting, but not a whole lot of acceleration. Sure, to put it in perspective, on a typical day this will still be one of the fastest vehicles on the road, and on a rainy day it most often is the fastest and most capable vehicle on the road. But I was used to more, and I wanted more. Much more.

 Exhaust:

The biggest restriction to most turbo engines is the exhaust system. A lot of people believe that turbochargers tap into some kind of "free" energy within the engine, using wasted exhaust gas energy to spool up and compress air into the intake. This is simply not true; the presence of a turbocharger on the exhaust causes vastly enlarged backpressure (often as much as 20PSI and higher) and this backpressure makes it more difficult for the engine to move exhaust out and take fuel in, reducing its power and efficiency. Obviously, the largest gains possible come from using a bigger turbo. Still, there are large gains to be had by freeing up the exhaust system itself. Since I lived in Michigan, I opted for an Invidia 3" catless downpipe.
 Also, very mindful of the Boxer Engine's unique Intercooler configuration: right on top of the engine where it soaks up heat from the exhaust and becomes an interheater, I had every single piece in the exhaust system first coated with high temperature ceramic insulation, then wrapped in Thermotec Gen 2 exhaust wrap. The insulation was so successful that I could always touch the exhaust pipes, no matter how hot the engine was. By far, the largest gains on this engine were had from the downpipe.

 Headers:

I probably wouldn't have done headers on this car right away, but it came with them. These were GT-Spec equal length headers with a 4-into-1 merge collector and an included large diameter up pipe. The headers are vastly less restrictive than the factory cast iron piece, and open up the way for very large power gains when coupled to big turbos, which are choked by the small primaries of the factory piece. However, there are two downsides to running headers in a turbo car:

1- The same larger pipe diameter that allows more horsepower at the top end through lower restriction also causes increased lag, as the exhaust gases have a larger space to fill before reaching the turbine and ding work to it.

2- The factory headers are thick and made of cast iron; they retain heat a lot better than the thin wall stainless steel aftermarket headers are made of; because of that, they allow the gases to cool down before reaching the turbo. As gases cool down, they contract, causing a further increase in turbo lag. Coupled with the fact that all that heat loss rises up and heat soaks the intercooler, I would recommend never running uninsulated headers on a turbo car. I had these out for ceramic coating after only driving with them for a month. Once removed, I also noticed that their equal length design made the car lose a lot of its characteristic "Boxer Burble" exhaust note.
Overall, I would say that headers are a must on any big turbo / maximum effort car, and that they should always e ceramic coaetd or wrapped. On a factory car they also produce gains (somewhere in the order of 10whp), particularly when tuned for, but are not the most cost effective modification (I probably had around $1000 into these by the time they were coated and wrapped and ready to do).

Catback Exhaust:

Borla Hush, twin tip. WOW! Is all I can say. After dealing with numerous loud, obnoxious aftermarket exhaust systems that would thunder and resonate, setting off car alarms and getting me pulled over, I can honestly say that I hit the jackpot with this lifetime warranty, all stainless steel system from Borla. It produced one of the nicest exhaust notes I have ever heard in any vehicle, and was just loud enough, but never too loud. It also lacked a stupid 4+ inch diameter tip that seems to be the norm in the import world, making cars like this prime target for law enforcement. I  recommend nothing else.

Intercooler:

 In a turbo car, intake air teperature is everything: on boost, you will make as much power as you can intercool into your engine.

Brakes, Tires and Traction:

Girodisk 2 piece lightweight brake rotors, Racing Brake semi metallic street/track pads and Falken Azenis RT-615 tires, sized 2 sizes up for 245 40 17.

 Interior:

 

Pillar: Boost and Air/Fuel Ratio
Center Console: Oil pressure, EGT and XM receiver
Steering wheel: KnockLink detonation monitor.

Under Construction!

Under Construction!

Under Construction!

Under Construction!

The new car