The main differences between the FA and EJ engines

Welcome again on our Blog! In this edition we are going to break down for you the differences between the two main Subaru engine platforms; EJ and FA.

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The EJ Engines

The EJ platform is a big family that contains a few variations. The Flat 4 H4 engine was designed in the late 80s and hit the market in 1989 before becoming more commonly used in the Legacy and Impreza chassis in the early 90s. It is still in use today in the 2021 Sti. All EJ engines uses a shotbloc casing that separates in two, in the center of which sits the crankshaft. The rotating assembly is completed by two pairs of rods and pistons that are moving in opposite directions. All common versions uses 8 valves in each head, with a mix of one or two camshaft(Sohc or Dohc) depending on the version or generation.

It's an engine that has been used under different displacement accross all markets(North America, Latin America, Japan, Australia, Europe);

• EJ15 (1,5L) Jdm Impreza Gc1 & 93-06 Impreza in Latin America
• EJ16 (1,6L) 93-06 Impreza in various part of the world
• EJ18 (1,8L) Impreza Gc6 93-99 - Legacy 90-96
• EJ20 (2,0L) 89-19 in various Impreza, Legacy, Forester etc chassis
• EJ22 (2,2L) 95-01 Impreza & 90-99 Legacy
• EJ25 (2,5L) 94-21 in various Impreza, Legacy, Forester etc chassis

The FA engines

 The FA platform on it's side really is the newcomer in the Subaru world. The still Flat 4 H4 engine first appeared in the North American market in the 2012 Impreza(under the FB code) and is currently gaining more and more chassis each year;

• FA20D (2,0L non turbo) 12-20 Brz/Frs
• FA20F (2,0L turbo) 14+ Forester Xt & 15+ Wrx
• FA24F (2,4L turbo) 19+ Ascent & 20+ Outback Xt

All FA engines are still using a two-part casing with a centered crankshaft and two pairs of oppositely mounted rods and pistons. Appart from some newly angled rods, the shortbloc is very similar to the EJ with the exception of various measurements. Timing is taken care of by a dual timing chain and quad AVCS(Active Variable Camshaft System)system, cylinder heads each have 8 valves total(4 per cylinder) and uses two camshafts per cylinder head. The EJ valve bucket system however have been replaced by a lifter-type system in the FA engines.

As of now(early 2021), rumors are that the next Sti could finally transit over to the new FA engines with it's own version of the FA24.

More informations

It's important to understand that since the EJ engine has been in our cars for 30 years, Subaru went all in when adapting new technologies such as;

• Replacing the timing belt system with a no-maintenance timing chain system
• Replacing the port injection system with the direct injection system
• Leaving the undersquared Bore-to-Stroke ratio to use a perfectly squared ratio(86:86)

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