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2004 Subaru WRX STI - Project STI

Mike Kojima
Jun 1, 2006 SHARE
0606_turp_01z_subaru_wrx_sti+project.JPG Photo 1/1   |   2004 Subaru WRX STI - Project STI

Subaru WRX STi or the Mitsubishi Lancer EVO. Many believe that the battle for who reigns supreme in the sport compact car market is between these two cars. Both cars are formidable weapons in battle. Both cars have similar performance envelopes. Both cars turn nearly equal times around a racetrack. Yet somehow both cars feel and drive quite differently.

The EVO is like a scalpel. The steering is precise and quick, almost to the point of feeling darty. It is very easy to drive fast, it tends to understeer, yet under throttle the front wheels tuck in and the car tightens its line. When lifting off the throttle in a turn the car will maintain control, simply tightening the line. With a ham-fisted, unskilled driver it will gently transition to oversteer. It is forgiving to the uninitiated. I have a way of describing this car. If you find yourself going too fast into a turn, it's almost like the car tells you: "Oh dear, here-let me take it," and somehow you make the turn. That's how good the stock EVO is.

The engine is somewhat pipey, defiantly feeling like the turbocharged small displacement engine it is even though the turbo is remarkably lag free. The engine does have an ample amount of power in stock form. It is a highly-developed engine with a long history of achievements in the world of motorsports from import drag racing to WRC. Thus, the engine has huge amounts of support in the aftermarket with a wide selection of parts.

The big Brembo brakes are superb, the pedal is firm and the stopping is fade free unless under racing condition, in which case a simple change of brake pads will upgrade things enough to work.

Does it sound like I love the EVO? In fact I do to the point where it is perhaps my favorite car for any amount of money.

However, this series isn't about the EVO, it's about its archrival, the Subaru WRX STi. The STi is about as opposite to the EVO as can be. If the EVO is a scalpel, the STi is a sledgehammer. Both are deadly weapons that can kill instantly, they just differ in their approach.

The STi has a huge amount of grip, however, its balance is not as delicate as the EVO's. The STi will understeer in a corner and as the throttle is applied, will understeer more. Apply a little more throttle and it will suddenly and almost violently transition to oversteer. The steering has a rubbery feel and does not return to center consistently. The shifter has the same rubbery feel.

The EJ25 has superior bottom end power and torque. The engine quickly shoots through the transmission's six speeds. It does seem to run out of breath at high rpm though. Although this is the opposite of how an EVO feels, both cars return remarkably similar 0-60 and 11/44 mile times. The engine has a computer-controlled drive-by-wire throttle, which makes it more difficult for aftermarket tuners to fiddle with and it does not enjoy nearly the same amount of aftermarket support as the EVO's 4G63.

Although the STi has the same big Brembo brakes as the EVO the pedal feel is not as good and the brakes are more difficult to modulate. Flex somewhere in the spindle or caliper mount makes the car susceptible to brake caliper piston knockback which makes consistent braking under track conditions more difficult than with the EVO.

When driving both cars around the track I have turned nearly identical lap times but with the EVO I marvel on how easy it is. With the STi, I feel like, Whew, that was a lot of work.

For this project in the months ahead we are going to improve upon the STi's strong point, mainly its torquey and tractable engine, making it much faster while keeping its streetable and road raceable characteristics. Mostly we'll be paying a lot of attention to improving the cars weak points, the handling and braking. Project STi's goals will be to keep its easy street persona while being able to rip the 11/44-mile in the 11s and also win a Time Attack.

We are going to do extensive suspension work to improve every aspect from the geometry to the damping. Our brake work will bring out the full potential of the Brembos and we will work to exploit every possibility for easy bolt-on power.

We started with a used 2004 STi bought from a private party. Although the car was in mint condition and essentially stock, it was equipped with some sort of horrible aftermarket lowering springs that lowered the car too much and were too soft. This led to bottoming out the front suspension under cornering loads and horrible understeer. Unfortunately, this is typical of aftermarket lowering springs. A car as good as the STi is in stock form it is easy for the typical aftermarket tuner to mess it up. We were unable to even come close to approaching the lap times of a stock STi at Streets of Willow Raceway. These springs will hit the garbage soon enough and we will replace them with adjustable dampers equipped with coil-overs.

The previous owner had curbed the stock wheels hard and probably ran the car through a carwash with unprotected rails scarring the wheels badly. This looked ugly. Mackin Industries saved the day and provide us with some ultralight forged bronze Volk CE28N wheels in 18x8.5 with a 44mm offset. The CE28N is a high tech, superlight forged wheel favored by touring car racers around the world. Each wheel weighs a feathery 18 lbs. Impressive for an 18-inch, wheel.

Our racing experience also tells us that the CE28N is an exceptionally strong wheel as I have personally banged many a set hard against FIA curbs and potholes on the track with no damage! We also needed some sticky tires in anticipation of our planned suspension mods and excess of power. We selected a set of 245/40-18 BFG G-Force KDW tires for all around wet and dry street performance. At a later date we will probably get a set of 17-inch wheels with some sticky R-compound tires just for track use.

As a first step we drained all of the fluids from the transmission, transaxle, differential, and engine and replaced them with synthetics from Motul. We will get more into these lubes at a later date. Next, we baselined Project STi on XS Engineering's 4WD dyno and were surprised with the results. Project STi spit out an impressive 246.3 hp and 241.8 lb-ft of torque.

In our next installments, we will try to see what some basic bolt-ons do to Project STi's power, start to tidy up Project STi's handling, and turn XS's Eric Hsu loose on tweaking the STi's factory ECU.

Finally, we plan to have a showdown, a war to settle the score. Project STi vs. Project EVO head-to-head. Who will win? Stay tuned.

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Sources

Mackin Industries
Santa Fe Springs, CA 90670
562-946-6820
http://www.mackinindustries.com
XS-Engineering
By Mike Kojima
55 Articles

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