When we last visited with our 2004 Subaru Impreza WRX STi, it received a much needed transplant. The "built" EJ257 engine under the hood experienced an unfortunate episode of oil starvation that shredded the main bearings. To get the STi back on the road, a stock shortblock was sourced and installed. With the block in place, the BorgWarner S200 turbocharger went back to producing boost, while XS Engineering's front-mount intercooler continues to take care of reducing the temperature of the aircharge. In the hands of XS Engineering's Koji Arai, the stock EJ257 block generated 363 horsepower and 319 lb-ft torque at 22.7 psi.

The Boxer Gets Buff

Now that the STi was back on the road, we returned to our original objective; to build a bigger, stronger engine. We started with a call to Brian Crower. He recommended his BC Brian Crower Stroker Kit. This kit includes a BC Brian Crower 4340 billet stroker crankshaft, BC Brian Crower Pro Series forged connecting rods and CP Pistons machined to Brian Crower's specifications. The stroker kit increases the bore by 0.5mm and the stroke by 4mm, effectively increasing the displacement from 2,457cc to 2,608cc.

Starting with the stroker kit, we sourced a new EJ257 block and sent it to Race Engine Development (RED). RED machined the block and dropped in a set of Darton International M.I.D. ductile iron sleeves. The M.I.D. sleeves feature a modular integrated deck which helps to brace the sleeves against the walls of the water jackets. Once the sleeves were set, the block made its way to Benson's Performance Engine and Machine. Dan Benson bored and honed the block before assembling the BC Brian Crower stroker kit. Benson balanced the rotating assembly and blueprinted the shortblock before sending it to Garage Tuning. Garage Tuning gave the EJ257 cylinder heads a 3-angle valve job before seating the STI valves, Cosworth valve springs and titanium retainers. The block and cylinder heads were then clamped together with ARP's head stud and case bolt kit.

Back To The Dyno

Once the block had been secured in the engine bay, the BorgWarner S200 turbocharger was bolted back into place. With the EcuTek software in hand, Koji Arai of XS Engineering reflashed the factory ECU once more with the new block. With peak boost at 19.4 psi, the stroker engine generated 386.6 horsepower and 340 lb-ft of torque. This is an improvement of 23 horsepower and 21 lb-ft over the 2.5-liter engine. Despite the lower boost levels, the additional 151cc's of displacement changed the shape of the power and torque curves. Both the torque and horsepower curves shifted, bringing power and torque on nearly 500 RPM sooner. At 4,000 RPM an additional 45 whp was realized, while at 6,000 RPM an additional 47 whp made its way to the ground. Peak horsepower at the wheels topped out at 386.6.

On The Way To The 500's

We're on the way to our target horsepower goals in the 450-500 horsepower range. Maxed out on pump gas, we're looking to test our 2.6 liter EJ257 with VP Racing's 117-octane Q16 race fuel. Another avenue to consider is a methanol/water injection system to chemically raise the octane and bring us up to our horsepower target. We may also beta test one of AEM's prototype stand-alone engine management systems designed for "drive-by-wire" systems. Stay tuned.