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FA24 Engine Guide

Chandler Stark

Meet Chandler

Chandler is an automotive expert with over a decade of experience working on and modifying cars. A couple of his favorites were his heavily modded 2016 Subaru WRX and his current 2020 VW Golf GTI. He’s also a big fan of American Muscle and automotive history. Chandler’s passion and knowledge of the automotive industry help him deliver high-quality, insightful content to TuningPro readers.

When Subaru announced the new 2022 WRX there was only one thing on everyone’s mind: Was it going to include the FA24 or not? When the answer was yes, WRX enthusiasts immediately threw up their hands in celebration. Finally, the FA20DIT from 2015 was getting a serious upgrade.

Subaru had initially introduced the FA24 boxer engine in 2019 in the Subaru Ascent to some pretty good reviews. However, they re-tuned the engine for its placement in the 2022+ WRX, limiting the torque but increasing horsepower. Subaru also came up with a naturally aspirated version of the FA24, which they put in the 2022+ Subaru BRZ.

Though the FA24 is still a relatively new engine, we’ve put together everything that is known about it so far in this guide. Below, we will look at its history, specs, design, reliability, and, most importantly, its performance. Let’s get started.

Subaru FA24 Engine - FA24 Specs, Reliability, Performance

Subaru 2.4 L Engine Specs

EngineFA24DITFA24D
Configuration16 Valve Flat 416 Valve Flat 4
Displacement2.4L (2,387 cc)2.4L (2,387 cc)
AspirationTwin-Scroll TurboNaturally Aspirated
Bore & Stroke94mm X 86 mm94mm x 86mm
Fuel SystemDirect InjectionDirect Injection
Head/Block MaterialAluminumAluminum
Compression10.6:112.5:1
Boost Pressure12 PSIN/A
Horsepower Output260-271 hp228-234 hp
Torque Output258-277 lb-ft-tq184 lb-ft-tq

FA24DIT Engine Design

Like nearly all other Subarus, the FA24 is, of course, a horizontally opposed “boxer” style engine. The FA24DIT is based on the outgoing FA20DIT (FA20F), a 2.0 L engine Subaru first introduced in 2012. The FA24 is a 2.4 L, flat-four, turbocharged engine with direct injection. Subaru increased the bore from 86mm to 94mm to get the extra 0.4 L of displacement over the FA20DIT. It features an all-aluminum block and head, and has dual overhead cams controlled by a timing chain. Compression is unchanged from the FA20DIT at 10.6:1, and select models come equipped with an oil cooler to regulate oil temperatures. Also similar is the use of a twin-scroll turbo.

Twin-scroll turbos are more efficient and perform better than their single-scroll counterparts. The point of the twin-scroll design is to separate the exhaust gas pulses coming out of the exhaust manifold into two ports, or scrolls, which separately feed into the compressor wheel. This creates smoother flow from the exhaust into the turbo, which allows for better cam timing and more pulse energy. Subaru’s tuning utilizes this, in conjunction with direct injection, to massively increase power output and efficiency on the FA24. It results in an earlier and flatter torque curve, while increasing horsepower throughout the power band.

There is also a naturally aspirated version of the FA24, the FA24D. The FA24D supplements the engine’s direct injection with port injection, courtesy of the Toyota D-4S fuel system. This eliminates issues with carbon buildup while providing extra fueling for peak power. The compression ratio on the FA24D is raised to 12.5:1, to account for the lack of forced induction. Subaru also tuned the torque curve to be much earlier in the FA24D than its naturally aspirated predecessor, the FA20D.

Gasoline Direct Injection

The biggest carryover from the FA20DIT to the FA24DIT is the continued use of direct injection. Gasoline direct injection, or GDI or DI for short, is actually a relatively old technology that Bosch first developed in Germany in the 1950s. However, Subaru did not start to use the technology until the 2010s, with the FA and FB series of engines.

GDI fuel systems run at much higher pressure rates than traditional port fueling systems. They include high pressure fuel pumps that pressurize fuel at 2,000-3,000 PSI – 50x more than port fueling systems. GDI works by injecting atomized fuel straight into the combustion chamber rather than upstream. This allows for incredibly precise fuel injection timing, which massively reduces emissions while boosting fuel economy and performance.

The downside to GDI is the much higher manufacturing costs, as well as the added complexity of the systems. GDI fuel injectors are much more expensive than their standard counterparts, and GDI systems also add an extra fuel pump. There is the standard in tank fuel pump, as well as a high pressure fuel pump directly upstream of the injectors and fuel rails. Unfortunately, these high pressure fuel pumps have not always shown to be reliable, and they are expensive to replace. In addition, DI engines are subject to carbon build up on the intake valves.

Reliability

So far, early returns on the FA24 point to pretty stout reliability, but the engine is so new that data is very hard to come by. Virtually nobody has driven the naturally aspirated FA24D, so it is really anybody’s guess on that engine and what to expect. However, if the outgoing FA20s are any guide, there are a few things to look out for.

Number one is going to undoubtedly be carbon buildup on the intake valves. Carbon buildup occurs on the intake valves of GDI engines, because the location of fuel injectors does not allow them to spray fuel on the back of the intake valves to clean the carbon off. Typically, this is not too big of an issue, and 95% of owners will never experience problems related to excessive carbon buildup. In severe cases, it can cause poor idling, misfiring, and loss of power. The only prevention method is to periodically have your intake valves cleaned through a process known as walnut blasting. But again, it’s highly unlikely the average driver will suffer from these issues, as they rarely caused serious issues on previous GDI Subarus.

The other issue with the outgoing FA20DIT is weak connecting rods. Early 2015-2016 WRXs were notorious for throwing rods at relatively low mileage on tuned engines. However, the FA24 supposedly has improved piston design and stronger connecting rods, which should hopefully alleviate any lingering issues.

Apart from those, there have not been any widespread reports of problems with the FA24 engine. However, now that it is being pushed more to its performance limits, that might change.

Performance and Upgrades

Now onto the most exciting part of the FA24DIT: performance and mods. From the factory, the FA24 makes between 260-271 hp and 258-277 tq, depending on the application. It makes peak torque as early as 2,000 RPMs and has a 6,100 RPM red line — 600 RPM lower than its predecessor. The naturally aspirated FA24D makes 228-234 hp and 184 tq, depending on selected options for the BRZ. The BRZ makes torque a little later, at 3,700 RPMs, but it lasts until red line.

On the track, the FA20DIT makes the zero to 60 mph sprint in just 5.5 seconds, while its naturally aspirated brother does so a hair slower, in 5.9 seconds. The FA20DIT is also not surprisingly faster at the ¼ mile, making it in 13.9 seconds at 103 mph. Whereas the BRZ does it in 14.3 seconds at 98 mph. The FA24 only runs on 12 PSI of boost, 4 PSI less than the FA20, but it makes almost identical power. Off boost, the FA24 is much more responsive and powerful than its predecessor, a benefit of its larger displacement.

One of the biggest gripes with the new FA24 is that it is not anymore powerful than its predecessor, and that complaint does have some merit. Torque output is identical, while horsepower is only increased by 3. Some dynos have even shown the FA24 to make less horsepower than the FA20. However, while peak numbers might not be very flattering for the 2.4 L, the entire powerband is much improved. Gone are the unfortunate torque dips and uneven power distribution of the FA20. The new engine gives the car a larger mid-range and reaches peak torque earlier while holding it for longer.

FA24 Upgrades

Unfortunately, so far there is not a ton of aftermarket support yet for either variant of the FA24. It is unclear if FA20 WRX parts will fit the new engine, but it is not likely they will be direct fits. It looks like the industry will pretty much have to start from scratch with the new FA24s, as there is not even a well known tuning solution yet.

Yet, we do know a little bit about the power limits for the FA24. Prime Motoring swapped an FA24 engine out of an Ascent into a Subaru Crosstrek as part of a pretty monster build. It ended up making over 500whp on the stock block, and reportedly has held up pretty well without major issues. So, while it’s a stretch to say the FA24 is now definitely capable of putting down 500whp reliably, it is an indication these motors can take some future mods and abuse.

The FA24 Is Shaping Up To Live Up To The FA20’s Legacy

The FA24 engine is still pretty new, but so far it looks like it will be a great motor. Performance-wise, it has already shown some serious potential, and even in its stock forms it is no slouch. The combination of direct injection, a twin-scroll turbo, and increased displacement, will certainly make the FA24 formidable for the foreseeable future.

A lot is still unknown about the FA24, and there is virtually no aftermarket support – yet. But, as we have seen the Subaru community do continually, it’s likely only a matter of time before someone starts to crack the code. It will be interesting to see how the FA24DIT ages with the WRX and how the Subaru community grows with it.

Are you considering getting a brand new 2022 WRX or 2022 BRZ with the FA20DIT? Do you already have experience driving or working with one?
Let us know in the comments below!

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3 Comments

  1. Bought my first WRX (Orange Premium Manual) a week ago and am awaiting for it to arrive from the port (RI) to the dealership. I am so excited!!!!

  2. Considering purchase of Outback Wilderness with FA24DIT. A bit freaked about carbon buildup on intake valves. Cannot seem to find zny info specific to this engine about rate of buildup, previous owners’ experience, etc. Reviewed several chemical spraynsystmes to “clean” intake carbon, but none seem to deliver like a good old walnut blast. Trying to determine if this service would be 50k, 100k ot never? Probably gest to get a borescope into the intakes to look. Is this a difficult thing to do? Any/all replies appreciated.

    1. Hey Stephen,
      From my experience with the FA20 platform, which I would think is very analogous to the FA24, carbon buildup was never a problem for me or anyone else I knew with the car. It was rarely an issue that popped on forums, too. The consensus among most of us was that repeated short trips where the engine does not get up to operating temperatures was generally the biggest cause for too-much buildup. Just normal operation (and occasional spirited driving) was more than enough for excessive carbon to burn-off the valves and prevent issues from happening. In addition, the buildup comes on pretty quick, so most people who walnut blast find their valves just as dirty within <10,000 miles.
      Problems are not likely to crop up within 150,000 miles under normal driving conditions. But if they do, walnut blasting is a pretty safe and simple procedure. I would not worry about getting the service done until you need to, i.e. the car starts running rougher or you get a CEL for it.

      All the Best,
      Chandler

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