To most people stateside, converting to STi spec is merely adding the light covers and OEM badges. To be considered a fully-converted STi means physically pulling out the U.S.-spec five-speed transmission and 227-hp engine and replacing it with the 271-horsepower, J-spec model. Yeah, yeah we know, the U.S.-spec, 2.5 STi is 300 horsepower, but we chose the J-spec model. In any case it's still better than the standard engine. Since there are very few people that have attempted the swap, we decided to give it a shot. Before we got our feet wet we first had to get our hands on the setup, and just as luck would have it, a gentleman by the name of Ben Lake happened to call me and tell me he could get a low-mileage Subaru engine through Japan. After a quick meeting with him it turned out they are able to get used engines directly from Subaru at very low prices. We went through a distributor located in Canada, Four Star Motorsports, and an engine setup was on its way. At the time of the swap we only expected the key components needed to complete it but we ended up with a complete transplant to convert not only the engine to STi, but the whole vehicle to an STi. This included brakes, tranny, wiring harness and ECU.
When it comes to the STi engine's basic engine layout, it looks exactly like the U.S.-spec, 227-hp model but its main difference is its red intake manifold. What counts is what's inside. To start with, the bottom ends of the two engines are completely different. While the U.S. model comes with an open deck water jacket, the STi comes with a semi-closed deck for added strength. Other components that are beefed up to withstand turbo boost abuse include forged pistons and forged high-carbon steel connecting rods. Rods have been beefed up on the rod journal side and if any of you have thrown one of these out of the block, you know the most vulnerable point on the rod is closest to the rod journal. Adding more strength to the bottom end is a reinforced steel crankshaft, far superior to the U.S. spec. With just this bottom end alone, we have seen EJ20s from down under hit 450-and-up horsepower on the stock bottom end, even when they are daily drivers.
The key to putting the STi horsepower to the ground requires a transmission that can handle the power. For this we decided to stick with the STi six-speed transmission since it has been known to hold plenty of power. When comparing the five- and six-speed transmissions side by side the shear size of the six speed shows that it is more than an extra gear installed. In fact, other than the EJ20 engine's bolt pattern, the six speed doesn't share any similarities in gear ratio or design with the five speed. With a much longer tail shaft, we knew if we were to use this tranny we would have to swap out to a shorter driveshaft as well as the rear differential to match the front diff's gear ratio.
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