Subaru STI Performance Parts are found in a glossy 18-page catalog chock-full of short throw shifters, strut braces, exhaust systems, cold air intakes, transmission mounts, boost gauges, and more. Of course, one will also find the obligatory cosmetic carbon fiber add-ons, STI mugs, and Subaru-branded golf balls. While most of the parts are covered under the factory limited warranty, some of them are only covered under the limited parts warranty, and a few are sold "as-is" without any warranty covered (those are typically designed for "off-highway" or race applications only).



To give us an excellent back-to-back comparison between a stock and an SPT modified vehicle, Subaru brought four cars to the Streets of Willow Springs race track, located just outside the town of Rosamond in the California desert. There were two Impreza WRX models (one stock and one modified), and two Impreza WRX STI models (one stock and one modified). As an unexpected cherry on this ice cream sundae of an afternoon, Subaru also brought out its one-of-a-kind Forester XTI concept for its track debut. That's right, the SEMA show car custom-fitted with full STI running gear!

2009 Forester XTI (Concept)

• 2.5-liter turbocharged boxer flat-four
• Est. 315 hp / 300 lb-ft
• Six-speed manual
• Dunlop SP Sport 600 – Max Performance Summer Tires (200 A A)

As a one-off concept, we were understandably apprehensive about tossing this particular Forester into the corners at speed. To our amazement, however, it handled the circuit like a true champ. Entering the turns, the compact SUV displayed initial turn-in that inspired confidence (the underpinnings are slightly modified from the STI, not mirrored). While credit may go to the additional weight over the front end, that same mass becomes a slight penalty while exiting the sharper corners which took all 315 horses to get back to speed. We didn't push it that hard, but overall the XTI was balanced and easy to drive without any glaring shortcomings. Subaru's so-called "tarmac monster" delivered as promised. Now, we want to see it in the showroom!

2009 Impreza WRX four-door sedan (stock)

• 2.5-liter turbocharged boxer flat-four
• 265 hp / 244 lb-ft
  
• Five-speed manual
• Dunlop SP Sport 01 – Ultra High Performance Summer Tires (280 A A)

While the bone-stock Subaru WRX is a ton of fun as a daily driver on public roads, but when the new body style debuted, it simply became too domesticated for proper showroom-to-track duty. In fact, its inadequacies – starting with the suspension – surface in the first corner. When really pushed, the tallish ride height leads to pronounced body roll. The stock WRX suspension is soft and the body tends to float rather than settle down. The shift in weight unloads the inside tires and strips them of their contact patches. Pushed harder, the stock WRX will plow as the front outside tire is completely overworked. Adding power simply increases the tire howl without any significant directional change. Lacking firm suspension while sliding on street tires, the best way to recover is to get off the gas, wait for the vehicle to dump weight back on the inside springs, and then use the all-wheel drive grip to hustle the car around the corner. Driven at 8/10ths, and with weight transfer a mental priority, the stock WRX is safe and predictable... just not a slot-car ride on a track.

2009 Impreza WRX Five-Door (SPT modifications)

• 2.5-liter turbocharged flat-four boxer
• 265 hp / 244 lb-ft
• Five-speed manual
• Dunlop SP Sport 01 – Ultra High Performance Summer Tires (280 A A)
• STI Lip Spoiler
• STI Shift Knob 5MT
• STI Short Throw 5MT
• STI Shifter Bushing
• Strut Tower Brace
• Chassis Brace
• SPT Performance Exhaust 5D

The stock five-speed transmission feels great... until you try the short throw set-up. Then, you quickly realize how much it improves shift throw and feel without adding unnecessary effort or making the transmission feel too mechanical. We like it. Under the skin, this WRX is fitted with chassis reinforcements, but really no other suspension modifications. It also wears a throaty SPT stainless exhaust system. There must be some "mental horsepower" with the new exhaust, because the aggressive sound caused us to push this car much harder than the stock WRX on the track.

Seat of the pants, the chassis did feel a bit better, but lacking any direct suspension upgrades we found ourselves plowing and sliding into the corners yet again. Interestingly enough, something else surfaced: Driven at 9/10ths, our higher speeds were really starting to destroy the single-piston brakes. The stock pads were overheating and the rotors were getting chewed-up. Even worse, we noticed that heavy brake applications above 90 mph would invoke immediate ABS. With the wheels clawing for traction, the WRX would become uncomfortably unsettled on the stock suspension. While the short throw shifter and new exhaust was welcomed, we think the chassis-bracing modifications were a bit out of order – our money would focus on calming the struts, sways, and springs first, along with a new set of brake pads.

2009 Impreza WRX STI five-door (stock)

• 2.5-liter turbocharged flat-four boxer
• 305 hp / 290 lb-ft
• Six-speed manual
• Dunlop SP Sport 600 – Max Performance Summer Tires (200 A A)

The stock STI was immediately a noticeable improvement over both WRX models. With additional power, a more advanced AWD system (including the Driver Controlled Center Differential), and Brembo brakes, we were able to push it hard on the track. In stock showroom form, the high-performance STI still exhibited noticeable body roll and would eventually understeer, but after a few laps, it became easy to predict exactly how the vehicle would react. While we were absolutely killing the stock street tires, and the brake pads weren't up to heavy track duty, it was apparent that your Average Joe could hit the local circuit in a stock STI and spend his day plastered with a big grin.

2009 Impreza WRX STI five-door (SPT modifications)

• 2.5-liter turbocharged flat-four boxer
• 305 hp / 290 lb-ft
• Six-speed manual
• Dunlop SP Sport 600 – Max Performance Summer Tires (200 A A)
• STI Lip Spoiler
• STI Shift Knob 6MT
• STI Short Throw 6MT
• STI Shifter Bushing
• SPT Strut Tower Brace
• SPT Chassis Brace
• STI Pink Springs
• SPT Performance Exhaust System 5D

What a difference some good suspension tuning makes. This STI was fitted with the 6MT short-throw shifter and stainless exhaust. Both are must-have items that really complement the personality of this high-performance vehicle without sacrificing ride quality or comfort. Under the skin, the modified STI was equipped with chassis braces and new springs, lowering the ride height and firming things up.

On the race circuit, this STI was clearly top dog. It was incredibly stable in the corners – almost neutral – and we could really use its power to our advantage on the exits. Again, the tires and brake pads were the weak links, but those are both easy aftermarket fixes. This STI was outfitted very well for a combo daily driver/track role, as it never felt abusive or harsh in our hands (as dedicated track cars often do). With a set of R-compound tires and some race pads slipped into the meaty Brembo calipers, a vehicle configured like this STI would eat more than its share of competitors on the race circuit.



Bred on the competitive World Rally Championship circuit, the WRX and STI both offer an impressive amount of street performance straight out of the box. The track is a whole different animal, as was evident by the abuse the street tires and brake pads were taking on all of the vehicles (if you are going to regularly track any vehicle, do yourself a favor and invest in the proper tires and pads first). Competition consumables aside, there are countless aftermarket options when modifying an Impreza. And with factory engineering and designs proven in professional racing, Subaru owners would do well to check out the comprehensive list of SPT offerings.

Gallery: Subaru WRX with SPT

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Photos Copyright ©2009 Michael Harley / Weblogs, Inc., Subaru North America