Comprehensive FA20 engine guide

"All you ever need to know about tuning the FA20 Engine"

The FA20D fitted to the BRZ and GT86 use a Subaru engine design including variable valve timing in a boxer layout with a Toyota D-4s clever injection system combining direct injection and port injection to maximize efficiency and response.

The FA actually came after the FB subaru engine and boasted a new design and was optimized for lower weight. It shares little in the way of parts with the FB engine and was a quantum evolution of the design.

When Toyota and Subaru collaborate you get the FA20 engine which is fantastic.
  • Bore: 86 mm Stroke: 86 mm
  • Displacement: 1,998 cc
  • Compression Ratio: 12.5:1
  • Power: 197 hp at 7,000 RPM Torque: 151 lb·ft at 6,500 RPM
  • DOHC and VVT with a 1 3 2 4 firing order

Just take another look at the power figures? Yes you see 100bhp per 1000cc which is no mean feat for a NASP engine. It is just crying out for more power though.

Stage 1 mods: Lighter flywheel,Remap,Panel air filter,Sports exhaust.

Stage 2 mods: Polished head larger exhaust port, 3 angle intake valve grind,Fast road cam,Fuel injector & fuel pump upgrades, Power clutch

Stage 3 mods:Internal engine upgrades (pistons/head/valves), Adding or upgrading forced induction (turbo/supercharger), Engine balancing, Competition cam.

We've also come across some owners toying with twincharging conversions and making some impressively high power hikes but these are costly and difficult to setup.

Remapping the F20 will take power to around 215bhp, then if you add a high flow sports exhaust you'll see 225bhp. Things do get very hot in the engine bay and thermally wrapping the exhaust is considered essential and pushes power figures (with these other mods) to around 230bhp.

Keep the oil temps low as well, many of our FA20 owners fit an oil cooler to help with this.

FA20 forced induction (superchargers & turbo kits)

Superchargers are generally easier to add than a turbo and there are a few FA20 supercharger kits on the market at the moment. Note that turbos provide boost in exponential proportion to rising engine speed and this can make mapping difficult whereas a supercharger provides boost relative to engine speed.

If you wanted a turbo kit then we have seen the Mitsubishi TD05-20G turbo added successfully giving a peak of 10psi boost but TorqueCars recommend porting and flowing the head, fitting forged parts and getting a good quality boost controller and blow off valve.

The high 12.5:1 compression ratio, even with direct injection limits boost to around 7psi unless you use very high octane fuel and careful timing where you can push up to around 10psi. *(Some have seen 12psi working well but TorqueCars would caution you to avoid these peaks unless you are on E85 fuel and have a very good ECU tuner to hand).

Dropping in forged pistons and taking compression to 10.5:1 will allow you to run higher boost levels  on a forced induction setup. For NASP tuning you could increase the compression ratio to around 13.5:1 but OEM pistons are pretty reliable for NASP tuning projects.

Using an aftermarket ECU or good quality remap you can see power levels hit around 250bhp if supported with other mods.

Cosworth have done some interesting work on the FA20 and applying their motorsport experience have come up with a stage 2 Power package taking power gains on the full stage one kit from 230bhp to 280bhp. The kit includes a supercharger and front mounted intercooler.

We have seen some tuners hitting 450bhp with a turbo, giving a little indication in the potential for tuning these FA20 engines.

FA20 engine weakspots

Fuel pump upgrades and injectors are required when you want to exceed 300bhp or you will suffer from running lean.

Big valves enhance the already nicely setup head and a 3 angle valve job on the air intake. Enlarging the exhaust port will also assist your power goals.

Stock internals seem to be quite reliable upto around 300bhp. The first thing that struggles are generally the connecting rods. Forged rods (X beams are generally preferred) and ARP2000 bolts are usually good to 800bhp and rev happily to 9000rpm.

Keep an eye on oil pressure when tuning, if this drops to 50psi you will have problems. Ideally it should sit around 80psi or 70psi when on the track. The engine bearings should really have oil prioritized and this can be achieved through modification of the oil feed and crank.

Please help us to complete this article, use the feedback box below if you spot any errors or have any tips or comments to pass on to other FA20 engine tuners.

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