A wiring meltdown and spun bearing prompted William Deaton of Cincinnati to start with a fresh but certainly more powerful boxer engine combination for his 2008 Subaru Impreza WRX STi in this Homebuilt Horsepower edition. The foundation is a PSI Proformance shortblock in the stock 99.5 x 79.0 cylinder dimensions for a 2.5-liter displacement. It supports Manley rods and pistons that provide an 8.2:1 compression ratio.

The heads were cleaned and surfaced, then fitted with Supertech valves and beehive springs. The stock camshafts were retained but polished along with the bearings. Also stock is the intake and throttle body, but Deaton performed a TGV delete. Boost comes from a BorgWarner S300 83/75 turbo through a Mishimoto top-mount intercooler.

“The header is a no-name cheapie I’m modifying and having re-TIG-welded,” adds Deaton. “The up pipe is custom as well as the down pipe that started life as a stock Meagan racing pipe for an STI.”

Fuel is delivered via a Deatschwerks 275 lph tank-mounted pump to Injector Dynamics 1,000cc injectors.

“It’s still running the factory ECM, but I’m currently working on a plug-n-play harness to run a stand-alone Haltech,” says Deaton, adding the utilizes the factory SI-Drive knob to select from three different tunes. “I’m looking for 18 pounds economy, mid-20s on medium boost and 30 pounds on full boost.”

Other engine details include Perrin crank pulley, Gates Racing timing kit and Clutch Masters stage 3 clutch.

There’s still some work left, including wrapping the exhaust and stand-along lubrication for the turbo, but Deaton has a goal of 600 horsepower at all four wheels!

If you’re interested in submitting your garage-built engine to Homegrown Horsepower, send a few quality photos and brief writeup of the details to [email protected].