FB20: Everything You Need to Know | Specs and More

Subaru introduced the FB20 in 2010 as a replacement for the very outdated EJ engine family. The EJ family was used in nearly every single Subaru product since 1989 and Subaru still use them in the Impreza WRX STi. The FB20 was designed with economy in mind and features many technologies that allowed Subaru to improve their fuel efficiency. In this short article, we’re going to cover everything you need to know as well as specs.

FB20: Engine. Basics and Specs

Just like many Subaru engines of the past, the FB20 is a flat four-cylinder engine. The cylinder block and cylinder heads are made of cast aluminum to help save weight which also increases efficiency. The flat engine configuration helps keep the center of gravity low which inherently improves handling.

Subaru focused on creating a very lightweight rotating assembly to help improves efficiency. The connecting rods are asymmetrical and the pistons are extremely lightweight. Subaru also changed from a belt-driven valve train to a chain-driven valve train. This allowed them to decrease the angle on the valves allowing for a smaller cylinder bore. With that smaller bore came a slightly larger stroke which further increased efficiency.

  • Production Run: 2010 – Current
  • Cylinder Block Material: Cast Aluminum
  • Cylinder Head Material: Cast Aluminum
  • Weight: 350 lbs (Estimated)
  • Valvetrain: Dual Over Head Cams – Four Valve per Cylinder
  • Stroke: 90mm
  • Bore: 84mm
  • Discplacement: 1,995cc
  • Compression Ratio: 10.5:1 to 12.5:1
  • Horsepower: 146 horsepower @ 6,000 RPM
  • Torque: 145 lb-ft @ 4,200 RPM

Cars That Came With The FB20

The EJ engine family came in pretty much every Subaru produced after 1990. Although the FB series is fairly new, it will likely follow in the same footsteps of the EJ. The FB is currently used in the Impreza, XV, XV Hybrid, and JDM Forester. You may be thinking “doesn’t the BRZ use the FB20?” The BRZ and WRX use the FA20 which is closely related to the FB20.

  • 2011 – Current: JDM Subaru Forester (FB20B)
  • 2012 – 2016: Subaru Impreza (FB20B)
  • 2012 – Current: Subaru XV (FB20B)
  • 2016 – Current: Subaru Impreza (FB20D)
  • 2014 – Current: Subaru XV Hybrid (FB20X)

FB20: Known Problems

Since Subaru wanted this engine to achieve excellent efficiency they used a lightweight rotating assembly and a high compression ratio. This increased thermal efficiency which translated into a 2+ MPG increase. Those lightweight pistons, however, are known are having poor oil rings. Poor oil rings results in excessive oil consumption as mileage increases.

Other than the oil rings the FB20 is a pretty reliable little engine. It’s arguably more reliable than the EJ20 or EJ25 which are known for failed piston ring lands.

FB20: Tuning Potential

Subaru designed the FB for efficiency and as such didn’t utilize a very strong bottom end. The cars that use the FB20 aren’t performance oriented at all either. For this reason modifying the FB20 engine is pretty much never done. A simple intake and exhaust may pick up a couple of horsepowers, but anything past that is a bad idea. If you want something fast it’s better to just upgrade to a Subaru with a turbocharged FA20 or EJ20.

If you’re still craving more FB20 information we recommend checking out the Subaru Wiki page.

About Bryce Cleveland 249 Articles
Bryce founded Dust Runners Automotive Journal in 2014 as a way to write about the cars he found interesting. When he's not writing for Dust Runners he's writing for Power Automedia as a freelancer. He currently drives a 2015 Fiesta ST and absolutely loves it.

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