Understanding the FA24 Engine: A Modern Performance Platform

The Subaru FA24 is a 2.4-liter turbocharged flat-four engine that debuted in models like the 2022+ WRX, Ascent, Legacy XT, and Outback XT. Its closed-deck block, direct injection, and twin-scroll turbocharger make it a robust foundation for power upgrades. Stock output sits around 260 horsepower and 277 lb-ft of torque, but the engine’s design leaves substantial headroom. For enthusiasts, the key question isn’t just what can it make—it’s how much does each horsepower cost and whether the investment pays off in driving satisfaction and long-term value.

Unlike older Subaru platforms like the EJ series, the FA24 benefits from better thermal management and stronger internals from the factory. This means even mild modifications can yield significant gains without immediately requiring engine rebuilds. However, cost-effectiveness depends heavily on your goals, budget, and willingness to tackle installation yourself.

Below is a detailed look at common upgrades, their price ranges, and typical horsepower gains. These figures come from real-world tuning data and aftermarket pricing as of 2025.

UpgradeEstimated CostTypical HP GainCost per HP
ECU Tune (Cobb Accessport or Ecutek)$650 – $1,200 (including tuning software/cable)30–60 whp~$15–$35 per HP
High-flow Downpipe + Exhaust$800 – $2,00020–40 whp (with tune)~$25–$50 per HP
Upgraded TMIC / Front-mount Intercooler$500 – $1,5005–15 whp (mostly holds power)$50–$100 per HP (better for consistency than peak)
Upgraded Turbocharger (e.g., FP Green, Garrett G25-660)$1,500 – $3,500 (turbo + install kit)80–150 whp (with supporting mods)~$15–$25 per HP
Cold Air Intake (CAI)$250 – $6005–15 whp (tune recommended)$30–$80 per HP
Ethanol Flex Fuel Kit + Tune$800 – $1,500 (kit + custom tune)50–80 whp (on E60-E85)~$12–$25 per HP

Note: whp = wheel horsepower. Gains vary by dyno, altitude, and fuel quality. Costs include typical retail prices for parts, but installation labor is not included—add 15–30% if you cannot DIY.

Cost-Effectiveness by Upgrade Tier

Tier 1: The Budget Powerband (Under $1,500)

For owners looking to maximize value per dollar, the best first upgrade is an ECU tune. Cobb Accessport and Ecutek platforms can unlock 30–60 whp from the factory turbo with a conservative 93-octane map. Many tuners report the FA24’s stock fueling can support up to 340–360 whp safely with just a tune and a high-flow filter. Cost per horsepower here is unbeatable: under $20/HP.

Adding a cat-back exhaust for sound and minor flow improvement won’t hurt, but the real gains come from a downpipe. A catted downpipe paired with a tune often nets 40–50 whp for around $1,200 total parts. That’s roughly 25–30 dollars per horsepower—still very efficient.

Tier 2: The Sweet Spot ($1,500 – $4,000)

This tier includes flex fuel (ethanol) kits and upgraded intercooling. Ethanol is the single most cost-effective power adder for the FA24 after a tune. A flex fuel sensor, upgraded fuel pump (often the stock pump can handle E40–E60), and a custom tune can push the FA24 to 370–400 whp. The cost is roughly $1,200–$1,800, and the cost per HP drops to around $12–$20. However, ethanol reduces fuel economy by 20–30% and requires careful monitoring of ethanol content.

Upgrading the intercooler (either a larger TMIC or a front-mount) is less about peak horsepower and more about consistent power on hot days. While cost per HP looks high ($50–$100), the real value is preventing power loss from heat soak. For enthusiasts who track their car or live in hot climates, this is a must-have, shifting the cost-effectiveness equation from raw horsepower to usable horsepower.

Tier 3: Big Turbo and Beyond ($4,000+)

Once you replace the stock twin-scroll turbo with a larger unit, costs escalate quickly. A quality hybrid or ball-bearing turbo (e.g., FP Green, Garrett G25-660) with install kit, injectors, fuel pump, and custom tuning can easily exceed $4,000–$5,000. However, the power ceiling jumps to 450–550 whp. The cost per HP here can be as low as $15–$25, similar to a tune-only scenario, but the total outlay is much higher. Additionally, supporting modifications like an upgraded clutch, engine mounts, and a radiator may become necessary, pushing the true cost to $7,000+.

For daily drivers, the cost-effectiveness of a big turbo build is questionable unless you have a specific use case (drag racing, high-speed events). The added lag, reduced fuel economy, and increased maintenance burden can offset the adrenaline gains.

Hidden Costs: Installation, Tuning, and Maintenance

Many articles only quote part prices. Real-world cost-effectiveness must factor in labor, dyno time, and potential downtime. Professional installation of a downpipe or intercooler typically runs $300–$800. A custom protune on a dyno costs $500–$1,000. Cobb Tuning’s support documentation emphasizes that off-the-shelf maps are safe but leave performance on the table—a custom tune can net an additional 10–20 whp for the same parts.

Also consider hidden maintenance: higher horsepower stresses the CVT (if equipped), wheel bearings, and brake system. A manual transmission might need an upgraded clutch ($1,000+) when torque exceeds 350 lb-ft. The stock FA24 oil system is robust, but some owners add an oil cooler ($400+) for track days. These costs can double the initial upgrade budget.

Reliability and Longevity: What’s the Price of Power?

The FA24’s closed-deck block and strong rods are a significant advantage over older Subaru engines. However, reliability is not infinite. IAG Performance’s build guides note that on stock internals, 400 whp is a reasonable daily-driver ceiling with proper tuning (good AFR, conservative timing). Beyond that, you risk ring land failure or connecting rod fatigue, especially if running high boost on pump gas. The cost-effectiveness of pushing beyond 400 whp plummets if you factor in a $6,000 engine rebuild.

For most enthusiasts, the best balance of cost and reliability is a stage 2 setup (downpipe, tune, intake, ethanol) making 350–380 whp. This setup retains factory drivability, uses stock turbo spool, and costs around $2,500–$3,000 in parts. That’s roughly $7–$9 per horsepower from a baseline of 260 hp to ~370 hp—a 42% gain for a modest investment.

Real-World Examples: How Much Per HP?

Let’s look at two common build paths using real data from the NASIOC FA24 forum and personal builds:

  • Budget Build (WRX, manual): Cobb Accessport + custom tune ($1,000) + Borla cat-back ($800) = 310 whp. Total cost $1,800, cost per HP from stock (260 hp) = $36/HP. Driving experience improves noticeably, but gains are modest.
  • Ethanol Stage 2 (WRX, manual): Accessport + downpipe ($600) + flex fuel kit ($850) + tune ($600) + intake ($300) = $2,350. Expected 370 whp. Cost per HP from stock = $17/HP. This is widely considered the sweet spot for FA24 cost-effectiveness.
  • Big Turbo (Outback XT, CVT): Garrett G25-660 + injectors + fuel pump + intercooler + tune + CVT cooler = $6,000+. Expected 450 whp. Cost per HP from stock = $30/HP, but the CVT may limit durability and the Outback’s weight negates some of the thrill. Many owners report this feels overkill for a daily crossover.

The ethanol stage 2 clearly offers the lowest cost per horsepower, but the budget build may be more palatable for those who don’t want ethanol compatibility or warranty headaches.

Factors That Shift the Value Proposition

Initial Vehicle Cost

A new WRX starts around $33,000; a used Ascent might be $25,000. Spending $3,000 on a WRX with 260 hp makes sense if you intend to keep it long-term. On a $25,000 crossover, the same $3,000 represents a larger percentage of the car’s value—but if the car meets your needs otherwise, the upgrade can be highly satisfying.

Resale Value

Modified cars rarely recoup full modification costs. However, tasteful, well-documented upgrades (especially those that are reversible) can help you sell faster. A stage 2 WRX with a known tuner’s map and maintenance records may fetch $2,000–$3,000 more than stock, offsetting 50–70% of upgrade costs. Big turbo builds often scare off buyers, reducing the effective ROI.

Community and Driving Enjoyment

Cost-effectiveness isn’t purely monetary. The FA24 community on platforms like Reddit’s r/WRX frequently shares dyno sheets, data logs, and DIY guides. Learning to tune or install your own parts provides intangible value. Many enthusiasts report that the process of researching and building the car is as rewarding as the final horsepower figure.

Common Mistakes That Undermine Cost-Effectiveness

  • Buying parts without a plan: Installing an intake without a tune can actually lose power. Always plan upgrades in order of gain-to-cost ratio.
  • Neglecting fueling: The stock high-pressure fuel pump (HPFP) can become a bottleneck around 380–400 whp. Upgrading a part early saves re-tuning later.
  • Ignoring datalogging: A $650 Accessport that you never use to log is wasted money. Invest in a quality tuner who will review logs.
  • Overbuilding for street use: A 500 whp FA24 on a daily commute is rarely enjoyable—lag, heat, noise, and tire wear become issues. Match the power level to your driving environment.

Long-Term Benefits Beyond Horsepower

While the upfront costs of FA24 upgrades can be significant, the long-term rewards often justify the expense:

  • Improved driving engagement: A tuned FA24 with a responsive throttle and an ethanol blend transforms the vehicle’s character.
  • Enhanced reliability with quality parts: Upgraded intercoolers, oil coolers, and properly tuned fuel trims reduce operating temperatures and stress.
  • Community connection: Shared knowledge, group buys, and meets provide social value that money can’t quantify.
  • Potential fuel economy improvement: With careful tuning, some owners report slight highway mileage gains thanks to optimized AFR and spark timing (though ethanol drops overall MPG).

The Verdict: Is It Worth It?

For most Subaru enthusiasts, the FA24 is an exceptionally cost-effective platform. Starting at 260 hp, a $2,000–$3,000 investment can yield 370+ whp—a 42% increase at roughly $20 per horsepower. That compares favorably to many other turbo platforms (e.g., a BMW B58 might require $4,000 for a similar % gain). The key is to choose modifications that align with your budget and use case: ethanol and a downpipe provide the best bang for the buck, while big turbos are reserved for dedicated track or show builds.

Before spending a dime, set a clear horsepower target, research reputable tuners (Cobb Accessport or Ecutek are both excellent), and budget for supporting mods and a safety margin. If you can do basic wrenching, the cost-effectiveness improves dramatically. With thoughtful planning, the FA24 can deliver thrilling performance without breaking the bank—making it one of the most rewarding modern engines to modify.