If you've owned a Subaru WRX in the last decade, you've lived through the platform change. The EJ20 and EJ25 powered WRX and STI models for over 20 years. The FA20F replaced the WRX's EJ from 2014 in Australia. They're both turbocharged Subaru flat-fours, but they're completely different engines to work with.
This guide breaks down the differences that actually matter - for reliability, for tuning potential, and for building a car that lasts.
The EJ Platform: What You're Working With
The EJ series ran from 1989 through to 2021 in various markets. The EJ20T and EJ205 powered the early WRX; the EJ207 and EJ257 powered the STI and WRX STI variants. It's a long-stroke, cast-iron block design with aluminium cylinder heads. The EJ25 is the most common in the Australian used market.
The EJ's reputation is split. On one hand, it's a tuneable, proven platform with a huge parts ecosystem and decades of real-world feedback. On the other hand, the EJ25 has a well-documented susceptibility to head gasket failures - almost always traceable to cooling system neglect and overheating. Fix the cooling system and stay on top of maintenance and the EJ is genuinely reliable.
What makes the EJ special for builders: the parts ecosystem is massive, the tuning knowledge base is deep, and the aftermarket has had 30 years to engineer solutions to every factory flaw. If you know what you're doing, an EJ build is a well-mapped journey.
The FA Platform: What Subaru Changed and Why
The FA20F - aka the FA20DIT (direct injection turbocharged) - replaced the EJ in the WRX from 2014. It's shorter stroke, uses a direct injection fuel system, features a twin-scroll turbocharger, and sits in a more compact package. It makes more power from a smaller displacement (2.0L vs 2.5L for most EJ25 builds) and uses a timing chain rather than a timing belt.
The FA20 was Subaru's response to tightening emissions standards and the demand for better fuel economy alongside performance. It achieved both goals. It also introduced new challenges: direct injection carbon buildup on intake valves is a known issue over high mileages, and the FA20's cylinder 4 cooling characteristics mean it runs hotter than the other three under sustained load.
The FA20 represents modern Subaru engineering - more refined, more efficient, and in many ways more complex. The tuning community has caught up, but the depth of aftermarket development for the FA doesn't yet match the EJ.
Cast-iron block · Aluminium heads · Long-stroke · Timing belt · 30+ years of aftermarket · Deep tuning knowledge base
Aluminium block · Direct injection · Short-stroke · Twin-scroll turbo · Timing chain · Modern emissions compliance
Reliability: Where Each Platform Struggles
Head gaskets on the EJ25 are the most discussed failure - almost always cooling system related. PCV hose and connector degradation is common on high-mileage EJ engines and leads to oil consumption and smoking. The front camshaft seals, timing belt tensioners, and the air pump system are all service items with documented failure patterns.
Cold-start timing chain rattle is the most discussed FA20 issue - usually caused by tensioner drain-down overnight and typically harmless at 1-5 seconds, but worth monitoring. Cylinder 4 cooling is the bigger structural concern - the factory cooling circuit prioritises cylinders 1-3, leaving cylinder 4 running slightly hotter. Extended hard running, especially on track or in hot Australian summers, can accelerate head gasket wear on cylinder 4 specifically. The Fuji Racing Cylinder 4 Cooling Mod addresses this directly.
Performance Potential: Boost, Fuelling, Cooling
The EJ's long track record means there's a clear path for almost every build target. Single turbo conversions, built engines, larger injectors, flex fuel - the EJ has been done every way possible and the failure modes are well understood. A competent Subaru shop can get 300kW from a built EJ257 with a known, manageable risk profile.
The FA20 makes strong power in stock form (a stock FA20F WRX makes around 195kW at the wheels) and responds well to ECU tuning on E85 or flex. The limiting factor for high-power FA builds is still the bottom end - the aftermarket for FA bottom end builds is still developing.
For most street builds below 250kW, the FA20 is the cleaner, more modern solution. Above that, the EJ's deeper tuning ecosystem starts to make more sense.
| Category | EJ (EJ20 / EJ25) | FA (FA20F) |
|---|---|---|
| Displacement | 2.0L / 2.5L | 2.0L |
| Block | Cast iron | Aluminium |
| Fuelling | Port injection | Direct injection |
| Timing drive | Belt (replace every 80–100k) | Chain (no scheduled replacement) |
| Known weakness | Head gaskets (cooling related) | Cylinder 4 heat, carbon buildup |
| Street build ceiling | 300kW+ (built EJ257) | ~250kW (bottom end limit) |
| Aftermarket depth | Extensive - 30+ years | Growing - 10+ years |
| Best suited to | High-power builds, project cars | Street builds, daily drivers |
Parts Ecosystem: What's Available for Each
The EJ has 30+ years of aftermarket development behind it. Everything from OEM replacement parts to purpose-built race components exists and is well-priced. Roo Racing's EJ product range covers the full maintenance and upgrade spectrum - from genuine service kits through to cooling mods, PCV components, and performance hardware.
The FA20 ecosystem is growing quickly. Core maintenance items (genuine service kits, oil system parts, cooling components) are well-supported. The Fuji Racing Cylinder 4 Cooling Mod is specifically engineered for the FA20 platform's thermal management gap. The gap is in high-power build hardware - big turbos, built bottom ends - where the EJ still has the edge.
Which Platform Should You Build?
There's no universal answer, but the decision matrix is relatively clear.
- If you own an FA20 WRX (2014+) and want 200-250kW for the street and occasional track - stay on the FA, tune it well, address the cylinder 4 cooling, and maintain it religiously.
- If you own an EJ-platform car (WRX pre-2014, STI to 2022 in most markets) and want to build past 250kW - the EJ's aftermarket depth, known tuning map, and parts availability make it the smarter long-term investment.
- If you're buying a project car specifically to build - the EJ257 GDB/GRB STI platform offers the best combination of tuning infrastructure, parts availability, and potential for the price.
The FA20 is the better daily driver. The EJ is the better builder's engine - not because the FA can't make power, but because the EJ has 30 years of failure data, community knowledge, and aftermarket solutions behind it. Know which platform you're on, know its weak points, and buy the parts that address them. The factory left gaps in both engines. Roo Racing's job is to fill them.