The STI’s powertrain will feel immediately familiar to anyone who’s driven a highly strung Impreza: big on traction and robust and substantial through the gearlever and clutch pedal but not exactly straightforward to interact with.

Given the work put in to overhaul it, the new gear linkage should be slicker. As it is, it feels notchy and ponderous. But it’s only one constituent part of an engine and transmission combination that’s a bit of a monster: potent, sure – but demanding to use and generally unwilling to yield to your efforts to bring it to heel.

Matt Saunders

Chief tester
Subaru's engine gets a new ECU and bigger intercooler in the STI

Subaru’s turbocharged flat four might as well be a 1980s turbocharged F1 engine, given how peaky it feels compared with an equivalent modern turbocharged in-line engine.

Bury the pedal with less than 3000rpm showing and embarrassingly little happens; there’s a fair bit of turbo lag to push through, followed by a separate wait for the crankshaft to spin fast enough for the turbo boost to peak.

At 3500rpm the car begins to pick up; at 4000rpm it’s finally hauling. But that only gives you a 2500rpm sweet spot in which to aim to keep the crankshaft spinning in order to keep the car surging on.

Doing that means concentrating and timing your shifts with careful precision. And there will be lots of shifts, so short are the STI’s intermediate gear ratios.

That’s certainly an engrossing process, and we wouldn’t argue that the STI isn’t an involving drive. It’s characterful, too; seldom do you find modern performance cars in which you can feel the turbo boost building so vividly.

But if all of that sounds like we’re making excuses for the car, it’s because we are. Frankly, in this era of direct fuel injection and variable-geometry turbos, a £30,000 performance saloon should be more flexible, more responsive and just plain easier to drive quickly.

If the STI were all of those things, it would probably have broken the 5.0sec-to-60mph barrier – which is all it needed to do in order to be competitive with its current rivals. Instead, it languishes at least half a second off the required pace.

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