Subaru Impreza 485 HP 400 LB-FT Of Torque
Subaru's Impreza has been kicking up dirt on the world rally circuit well before the WRX was brought to American soil. Few Americans realize how capable the older Impreza models really were or at least could become after some modifications. Like many cars, they were noticeably lighter in weight back then, and offered a driving feel that many say are simply lacking in today's cars.
This '96 Impreza is possibly the most awe-inspiring example in the country. Originally purchased in 2003 by Michael Warfield of GST Motorsports, it was intended to be nothing more than his simple daily driver. It wasn't until years later, in 2006, that it began the transformation into this time attack monster. It all began when GST and partners GOTO:Racing and Calculated Risk were scratching their heads trying to figure out what car to enter in the NASA 25-Hour Endurance race that year. Brian Lock of GOTO:Racing suggested that Michael build up his old Impreza. With everyone in agreement, Michael called on engine-tuning legend Cosworth for some motor help. The car was stripped and the frantic wrenching began.
They managed to get the car ready with no time to spare, with the final dyno run being performed at 2 a.m. the night before the race. In a field of 55 cars, it qualified in Fourth Place, although mechanical gremlins caused the car to run only six hours of the actual race. Afterward, they decided it would become a dedicated time attack race car, and the crew got back to work.
With Cosworth still on board for the engine build and Prodrive now helping with the suspension, Michael knew it would be a serious performer as a time attack car. The centerpiece of the motor is the Garrett GT35R turbocharger, although GST has also been known to use a GT30R (along with 8.1:1 compression) configuration for less extreme duty. Air enters through the 4-inch K&N filter and is cooled through a Blitz intercooler, while excess is dealt with through a TiAL wastegate and blow-off valve. The plumbing was custom-fabricated by GST, including the 3-inch exhaust system, while the crosspipe is Injen equipment.
In order to cope with the extreme boost, the engine internals have been heavily fortified with forged Cosworth parts, including the crankshaft and connecting rods. The forged JE pistons (10:1 compression) and rings are also well suited at handling the high pressure. The stock oil system has been scrapped in favor of a high-capacity pump, pan, and windage tray, all from Cosworth. The oil is further kept cool with a Setrab core with a Mocal sandwich adapter. The Cosworth-spec cylinder head received just as much attention as the block. It features a complete Cosworth valvetrain, including camshafts, valves, springs, retainers, keepers, and rockers. It has also had a full CNC port and polish, all finished by hand.
The Bosch Motorsports 044 high-flow fuel pumps are further boosted by a pair of Walbro 255lph pumps, sending the high-octane gas to RC Engineering 1,000cc/min injectors. The swirl pot and fuel rails were custom fabricated by GST, and Aeromotive's fuel pressure regulator keeps it all in check. Ignition was left stock and is controlled by the Hydra Nemesis engine management system.
The latest dyno run shows that this setup is good for a consistent, reliable figure of 485 hp and 400 lb-ft of torque, going to all four wheels. In order to cope with this power, a new Spec C six-speed JDM transmission from Subaru was installed and customized. The clutch is an ACT unsprung six-puck unit, and the flywheel and pressure plate are also from ACT. Both the front and rear differential have been swapped for clutch-type units from Cusco.
Brake layout for the front consists of 340mm Stasis discs and four-piston Stasis calipers. For the rear, GST opted for STI-spec StopTech 316mm discs and two-piston Brembo calipers. Michael counts on Endless to supply the pads and Stasis for the braided brake lines.