2015-2021 Subaru WRX FA20DIT Modifications Guide: Intake, Exhaust, Tuning & Engine Mods

Introduction

The 2015–2021 Subaru WRX introduced a new era for the platform with the FA20DIT — a direct-injected, turbocharged 2.0L boxer four-cylinder engine. While it replaced the beloved EJ series, the FA20DIT is a capable and modern engine that responds well to modifications. With the right combination of intake, exhaust, tuning, and engine upgrades, you can unlock significantly more power while maintaining daily drivability.

This guide is specifically written for the 2015–2021 Subaru WRX with the FA20DIT engine.

1. Intake Upgrades

Why Upgrade the Intake?

The factory airbox on the FA20DIT WRX is designed to balance noise, emissions, and performance. An aftermarket intake allows the turbocharger to breathe more freely, improving spool response and top-end power. On a tuned car, intake upgrades can contribute to 10–20+ WHP gains.

Types of Intakes

• Drop-In Filter: The simplest upgrade — replace the stock paper filter with a high-flow panel filter. Minimal power gain but improved airflow and easy installation. No tune required.
• Short Ram Intake (SRI): Replaces the stock airbox with a cone filter closer to the turbo inlet. Better flow than stock, but can pull in warm engine bay air. Best paired with a heat shield.
• Cold Air Intake (CAI): Routes the filter away from the engine bay to pull in cooler, denser air. Better for power but more complex installation. Requires a tune on most setups.
• Turbo Inlet Pipe: Replaces the restrictive stock accordion-style inlet hose between the airbox and turbocharger. One of the best bang-for-buck mods on the FA20DIT — improves turbo response noticeably.

FA20DIT-Specific Note

The FA20DIT uses a top-mount intercooler (TMIC), so intake routing is different from the EJ-based STI. Make sure any intake kit you purchase is specifically designed for the 2015+ WRX FA20DIT.

2. Exhaust Upgrades

Downpipe

The downpipe is the single most impactful exhaust upgrade on the FA20DIT WRX. The stock unit is highly restrictive. Upgrading to a high-flow catted or catless downpipe dramatically improves turbo spool and top-end power. A tune is required after installing a downpipe.

• High-Flow Catted Downpipe: Retains a catalytic converter for emissions compliance. Best for street-driven cars in states with emissions testing.
• Catless Downpipe: Maximum flow, maximum power. Not street-legal in emissions-tested states. Best for track or off-road use.

Cat-Back Exhaust

A cat-back exhaust replaces everything from the catalytic converter back. On the FA20DIT WRX, this provides a sportier sound and minor power gains. Look for 3-inch diameter systems for the best balance of flow and sound.

Equal Length vs. Unequal Length

Unlike the STI, the stock FA20DIT WRX already uses an equal length header from the factory. This means you won't gain the same dramatic sound change from a header swap, but you can still benefit from a higher-quality aftermarket unit with better flow characteristics.

Shop our WRX Exhaust Collection for downpipes and cat-back systems.

3. Tuning

Why Tune the FA20DIT?

The FA20DIT WRX responds exceptionally well to an ECU tune. Even on a stock car, an off-the-shelf (OTS) tune can add 30–50 WHP by optimizing boost pressure, ignition timing, and fuel delivery. With supporting modifications, a custom tune can push the FA20DIT well beyond 300 WHP on the stock turbo.

Tuning Options

• Off-the-Shelf (OTS) Map: Pre-made tune for common modification combinations. Quick and affordable. Best for cars with bolt-on mods and no major engine changes.
• Custom Dyno Tune: Tailored specifically to your car, fuel, and modifications. Maximum power and safety. Recommended for any car with significant modifications or unique setups.
• E85 / Flex Fuel Tune: Ethanol-based fuel allows for significantly more aggressive timing and boost. The FA20DIT loves E85 — expect 30–40+ WHP over a 91-octane tune with the same hardware.

Popular Tuning Platforms for the FA20DIT WRX

• Cobb Accessport (most popular, user-friendly)
• EcuTek
• COBB + ProTune (best of both worlds)

4. Engine Modifications

Intercooler Upgrade

The stock top-mount intercooler (TMIC) on the FA20DIT WRX is a known weak point. Under sustained boost or in hot weather, it heat-soaks quickly, causing power loss and potential knock. An upgraded TMIC or a front-mount intercooler (FMIC) conversion dramatically improves charge air cooling.

• Upgraded TMIC: Drop-in replacement, no major modifications needed. Best for street builds up to ~350 WHP.
• FMIC Conversion: Moves the intercooler to the front of the car for maximum cooling efficiency. Requires piping modifications and a tune. Best for high-power builds.

Browse our WRX Intercooler options for TMIC upgrades and FMIC kits.

Fuel System

At higher power levels (300+ WHP), the stock fuel injectors and fuel pump can become limiting factors. Upgrading to larger injectors and a high-flow fuel pump is essential for E85 builds or any car pushing beyond stock turbo limits.

Turbo Upgrade

The stock FA20DIT turbo (IHI VF48) is capable of supporting around 300–320 WHP on a good tune. Beyond that, a turbo upgrade is necessary. Popular options include the VF52, VF54, and various aftermarket journal or ball-bearing turbos that offer faster spool and higher flow.

Recommended Modification Sequence

1. Start with a tune — even on a stock car, this is the best first mod
2. Downpipe — biggest single hardware gain, re-tune required
3. Intercooler upgrade — eliminates heat soak, especially important in summer
4. Intake + turbo inlet pipe — improves spool and top-end breathing
5. Cat-back exhaust — sound and minor power improvement
6. Fuel system upgrades + E85 tune — for maximum power on the stock turbo
7. Turbo upgrade — when you've maxed out the stock unit

Final Thoughts

The FA20DIT WRX is a modern, capable platform that rewards a systematic approach to modifications. Start with a tune, add supporting mods, and always make sure your fuel and cooling systems can support your power goals. With the right parts and a good tune, a 2015–2021 WRX can be a genuinely fast and reliable performance car.

At XT Performance, we stock performance parts specifically for the FA20DIT WRX. Browse our full catalog or contact us for fitment help.