Subaru FB engine

 An entirely new generation of boxer engine announced on 23 September 2010. By increasing piston stroke and decreasing piston bore, Subaru aims to reduce emissions and improve fuel economy while increasing and broadening torque output over the previous generation engine.

The FB has an all new block and head. It has DOHC, with intake and exhaust variable valve timing (AVCS - Active Valve Control System), and a timing chain that replaced the timing belt. Moving to chain-driven cams is said to allow the valves to be placed at a narrower angle to each other and shrink the bore of cylinder from 99.5 mm to 94. It results in less unburned fuel during cold starts, thereby reducing emissions. Subaru is able to maintain the exterior dimension substantially unchanged by asymmetrical connecting rods like those in EZ36. The FB is only marginally heavier. Car and Driver is told direct injection will be added soon. Subaru claims a 28-percent reduction in friction losses, mainly due to lighter pistons and connecting rods. The FB has a 10% improvement in fuel economy with the power coming on sooner and the torque band being broader.

• FB16: 1,600 cc, DOHC, 78.8 mm bore x 82 mm stroke, 10.5:1 Compression Ratio,

Rated at: 84 kW (115PS) @5,600 rpm, 150 Nm (15.3 kgm) @4,000 rpm in (2012+ EUDM Impreza XV 1.6i)

• FB20: 1,995 cc, DOHC, 84 mm bore x 90 mm stroke, 10.5:1 Compression Ratio,

Rated at: 109 kW (148PS) @6,000 rpm, 196 Nm (20 kgm) @4,200 rpm in (2011+ JDM Subaru Forester),

Rated at: 145 hp, 145 lb·ft (2012+ Subaru Impreza)

• FB25: 2,498 cc, DOHC, 94 mm bore x 90 mm stroke, 10.5:1 Compression Ratio.

Rated at: 170 hp, 174 lb·ft @ 4,100 rpm (2011+ North American Subaru Forester, 2012+ North American Subaru Legacy)