The Impreza WRX STI is no longer an Impreza. Subaru UK dropped the prefix three years ago in an effort to distance the turbocharged 4x4 from the more ordinary Impreza hatches it was trying to sell at the time.
The passage of those three years hasn’t, however, made the idea of an Impreza STI that isn’t an Impreza at all seem any less strange to us. Subaru stops short of calling this a ground-up new car, but there’s not a lot that has been left untouched.
The new bodyshell is wider, lower, longer of wheelbase and 140 percent stiffer than that of the last STI saloon, giving notable improvements in ride and handling, they say. The bodywork, too, is all new, and to our eyes it’s a marked improvement on the bland amorphousness that went before.
The suspension has been modified rather than replaced. Stiffer cross-members and bushings feature front and rear, as well as thicker anti-roll bars and slightly altered mounting points that increase toe-in at the back and ground contact under load at the front. The hydraulic power steering has also been replaced, with a stiffer column and quicker gearing fitted.
The engine and drivetrain remain largely unaltered. That means you get 2.5 litres of burbling flat four driving all four wheels via a six-speed manual gearbox (with a shorter throw and new scissor springs and detent profiles) and through a viscous limited-slip centre differential with driver-selectable front or rear bias.
The ‘EJ257’ 2.5-litre flat four gets a revised ECU, a bigger intercooler and exhaust gas recirculation for this new STI, helping it to pass Euro 6 emissions tests. The engine is mounted low in a boxer configuration, so it gives the car a low roll axis, but the layout also causes some problems.
There’s no direct injection or variable-geometry turbo technology here. Neither has Subaru found a way to shorten the inlet tracts between the cylinder heads and centrally mounted turbocharger, which would help engine response.
Subaru also runs up against a packaging problem that forces it to run oversquare cylinders in a big-capacity engine. A slightly undersquare, longer-stroke design (such as most of the rest of the industry use for better low-end torque) would force the cylinder heads even further from the turbo and might not even fit between the suspension turrets.