Subaru FA (2.0 and 2.4)

Subaru's direct-injected flat-four — the FA20 in the BRZ and the turbocharged WRX, and the FA24 in the current WRX and Ascent. The naturally aspirated FA20D in the BRZ was co-developed with Toyota, which fitted it to the GT86 and GR86 as the 4U-GSE, using Toyota's D-4S port-and-direct injection.

That joint origin is worth knowing because it means BRZ and GT86 material is interchangeable, and because the D-4S dual injection keeps the intake valves clean — so the carbon problem common to direct-injection engines does not apply to the naturally aspirated version in the way it does elsewhere.

The naturally aspirated FA20D's known characteristic is a pronounced torque dip in the mid range, which is a design property rather than a fault and is regularly reported as one. On the turbocharged FA20F and FA24F, the themes are the usual ones for a boosted direct-injection engine, with heat and oil condition mattering more than on the naturally aspirated cars.