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

FA20D (Toyota 4U-GSE): 1998 cc DOHC 2013-

  • Subaru BRZ
  • Toyota 86

FA20F DOHC turbo, 2012-

  • JDM Subaru Legacy 2.0GT DIT and 2014
  • Subaru Levorg 2014
  • Subaru Forester XT
  • 2015+ USDM Subaru WRX

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.

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Best Engine Mods for your FA20

  1. Mapping - remaps provide the most advantage in power for your outlay. There are a few anomalies with the FA20 so we recommend you use a specialist who knows these cars.
  2. Fast road cams are one of the most significant mechanical changes, but they must be installed by someone who knows what they're doing and they are not always easy to source but you might find a local firm to regrind a stock camshaft.
  3. Intake and Exhaust - Note that on their own these mods will NOT ADD POWER in most cases, but they can help enhance power after other mods by removing the restriction. Focus on the headers and cat and you'll see an improvement.
  4. Upgrades to turbochargers and superchargers - forced induction is the most efficient approach to increase air supply, allowing you to burn more fuel and make more power, there are a few decent BRZ kits around. For the cost this should net you the largest power gain.
  5. Head work - The goals of porting and flowing the head are to get air flowing into the engine while removing flow restrictions and turbulence.

FA20 Tuning stages

Typical stage 1 mods often include: Lighter flywheel,Remap,Panel air filter,Sports exhaust.

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

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

NASP engines need quite a lot of work when you add a turbo, so we have a separate guide to help you take into account the pros and cons of going this route on your FA20

Remapping the FA20

A decent tune combined with headers and decent exhaust should net around 10-15% more power.

TorqueCars recommend you do the mapping last so it can take into account all your other mods, and will fully release the power from all of the mods and upgrade.

Remapping the F20 will take power to around 215bhp, then if you add a high flow sports exhaust you'll see figures around 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.

Cam timing and ignition timing improvements will help iron out the torque dip on the BRZ engine. Some of this is down to the 8 injectors used, which have crossover and this causes peaks and dips, but when a tuner knows the BRZ well he can smooth out the power delivery and provide a much flatter wide torque curve that suits the nature of the car.

FA20 Turbo Upgrades

The more air you can get into an engine, the more fuel it can burn and uprating the induction with a turbocharger upgrade makes superb power gains.

When the engine is fitted with a turbocharger upgrades are more reliable and you will discover turbo charged engines are built with uprated components.

There are common areas of failure for every engine, with some being very over engineered and some just sufficiently able to handle stock power

See where you'll find these limitations and fit better pistons and crank to survive the power.

There are many mechanics spending a a stack of money on turbo charger upgrades on the FA20 only to suffer the indignity of watching the car throw a rod just after it's used on the roads.

Large upgraded turbo chargers often suffer no power at low rpm, and smaller turbo chargers spool up really quickly but don't have the peak end bhp gains.

In recent times the market of turbo units is always moving on and we commonly find variable vane turbo units, where the vane profile is altered according to speed to lower lag and increase top end power.

Twin scroll turbo units divert the exhaust flow into a couple of channels and direct these at differently angled vanes in the turbocharger. They also boost the scavenging effect of the engine.

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

FA20 Fuelling

Don't overlook the need to pay attention to the fuelling when you are increasing the power - it makes the car more thirsty. Most tuners we speak with say to be generous with your flow rate on the injectors.

As a rule of thumb add 20% when specifying an injector, this takes into account injector deterioration and affords you some spare capacity should the engine require more fuel.

We think this one is common sense, but you'll need to match your fuel injector to the type of fuel your car uses as well.

All the following flywheel power targets will assume an injector duty cycle of 80% and a base of 58psi of fuel pressure at idle.

4 Cylinder turbocharged engines

  • 58 PSI 340cc/min 200hp
  • 58 PSI 511cc/min 300hp

4 Cylinder NASP engines

  • 58 PSI 285cc/min 200hp
  • 58 PSI 426cc/min 300hp

4 Cylinder supercharged engines

  • 58 PSI 312cc/min 200hp
  • 58 PSI 468cc/min 300hp

FA20 Exhaust

Only look to replace your exhaust if your exhaust is creating a restriction in flow.

On most factory exhausts you should find that the exhaust flow rate is still ok even on modest power gains, but when you start pushing up the power levels you will need to get a better flowing exhaust.

Exhaust manifolds are a potential area for improvement on the FA20, there is a well documented torque dip.

A set of unequal length exhaust headers and tune can help mitigate this, but this is usually at the expense of a little top end power. Bear in mind you'll spend most of your time in the mid rpm range, so losing a little top end is a minor downside.

Sports exhausts can help increase the flow of gases through the engine.

But if your exhaust is too large, ie: it's over 2.5 inches bore, you will lose a lot of your flow rate and end up lacking power and torque.

Typically exhaust restrictions come around the catalysts installed, so adding a freer flowing high performance aftermarket one will improve air flow, and rather than doing an illegal decat, will keep the car road legal.

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.

FA20 Supercharger kits

When you want significant performance gains, it makes sense to fit a supercharger kit. These pretty much bolt on and with fuel and timing modifications you can totally transform the power output of your FA20 engine.

Expect to pay quite a lot for the kit, but bear in mind the power return will more than make up for this initial expense.

It is not unusual that there is a limitation in the air flow sensor MAP/MAF/AFM on the FA20 when loads more air is being drawn into the engine.

Going up you'll find 4 bar air sensors coping with quite large power gains, whereas the OEM air sensor was restricting performance at a much lower level.

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.

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 up to 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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