Moving to chain-driven cams is said to allow the valves to be placed at a more narrow angle to each other and shrink the bore of cylinder from 99.5 to 94 mm (3.92 to 3.70 in).

Subaru is able to maintain the exterior dimension substantially unchanged by using asymmetrical connecting rods like those in the EZ36 engine.

[4] Subaru claims a 28-percent reduction in friction losses, mainly due to lighter pistons and connecting rods.

[1] The FB has a 10% improvement in fuel economy[1] with the power coming on sooner and the torque band being broader.

All FB20 variants: The existing FB20B was modified by reducing internal friction for the hybrid drivetrain, which incorporates an electric motor in the Lineartronic CVT.

[13] Used in the fifth generation Impreza sedan and hatchback; compared to the FB20B, the FB20D adds direct injection, providing a slight increase in power and efficiency.

[4] All FB25 variants: The 2019 model year Subaru Forester was introduced at the 2018 New York International Auto Show with a revised version of the FB25 engine featuring direct injection, resulting in a slight boost in power and fuel economy.

[31] The seventh-generation 2020 model year Legacy and Outback also adopted the revised direct-injection FB25D as its base engine.