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March 11, 2011


The New Subaru FB20 Boxer Naturally Aspirated Engine


The New Subaru FB20 Naturally Aspirated Engine

Original Translation from “Proud of Boxer. Technology and passion for Subaru Boxer Engine.”







FB20 has the following specifications

Engine Form: 4-Cylinder DOHC Flat Engine

Engine Type: FB20

Engine Displacement: 1995cc

Bore x Stroke: 84.0 x 90.0mm

Compression Ratio: 10.5

Maximum Output: 109kW/6000rpm

Maximum Torque: 196Nm/4200rpm










FB20 Versus EJ20


EJ20 (Gasoline)

FB20 (Gasoline)

Engine Displacement



Bore Pitch



Bore x Stroke

92 x 75mm

84 x 90mm




Cam Drive System


Rocker Arm

Valve Angle

41 degrees

27 degrees

Fuel Injection Method








The Bore pitch remained at 113mm to keep room for the 2.5L version. The longer stroke improves the fuel Efficiency, and even with longer stroke, the engineers were able to maintain the new FB engine close to the dimension of EJ engine.


The new TGV (Tumble Generator Valve) on the FB20 has a new flap feature to adjust the air flow to the intake chamber. The FB20 also features an in-port fuel injection, a major change from the EJ predecessor. The fuel injectors are located on the cylinder heads to improve fuel efficiency and reduce gas emissions.






In-port injection



Breaking down the internals of FB20




The valve is direct bolt-on with cam angle at 410 with cam distance of 126mm on EJ engine.





FB20 uses roller rocker on the valve to retain the engine width and reduce friction loss. Valve cam angle is reduced to 270 and cam distance to




Smaller bore on FB20 engine





FB20 Cylinder head, separate pieces from the cam carriers, reducing the weight





FB20 Connecting rods shaped to engine width similar to the EJ. FB20 piston is smaller. The crown design is to maintain tumble flow’s momentum.

























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