The FA20 engine has become a modern icon among sports car enthusiasts. Developed jointly by Subaru and Toyota for the Subaru BRZ, Toyota 86, and Scion FR-S, this 2.0-liter naturally aspirated flat-four is celebrated for its low center of gravity, high-revving nature, and excellent throttle response. However, its modest 200-horsepower output leaves many drivers wanting more. The question on every enthusiast’s mind: what happens when you push the FA20 past its limits to produce 400 horsepower? This article compares the stock FA20 with a 400 hp build in real-world conditions on both the track and the street, based on data, hands-on experience, and community insights. We’ll examine what it takes to get there, how the driving experience changes, and whether the trade-offs are worth the investment.

The FA20 Engine: Anatomy and Stock Performance

Before diving into modifications, it’s important to understand what makes the FA20 special. This 2.0-liter boxer engine uses a unique combination of port and direct fuel injection, known as D4-S, to optimize efficiency and power. The dual injection system reduces carbon buildup on intake valves and allows for lean cruise conditions. The engine also features a high 12.5:1 compression ratio, which helps the stock engine deliver a surprisingly broad torque curve for a naturally aspirated four-cylinder. Stock power peaks at about 200 horsepower at 7,000 rpm and 151 lb-ft of torque at 6,400 rpm. The engine’s light weight — roughly 100 pounds less than a comparable inline-four — contributes to the car’s agility.

Stock Performance Figures

  • Displacement: 1,998 cc (2.0 liters)
  • Compression Ratio: 12.5:1
  • Power: 200 hp @ 7,000 rpm
  • Torque: 151 lb-ft @ 6,400 rpm
  • Redline: 7,400 rpm
  • Transmission: 6-speed manual or 6-speed automatic
  • Curb weight (manual): ~2,770 lbs
  • 0-60 mph: 6.0 seconds (manual)
  • Quarter-mile: ~14.5 seconds @ 96 mph

While these numbers are respectable, the FA20’s stock torque dip between 3,000 and 4,500 rpm is a known complaint. The engine feels flat in the mid-range, requiring the driver to keep revs high for maximum acceleration. This characteristic motivates many owners to explore forced induction.

Building a 400 Horsepower FA20: The Recipe

Reaching 400 wheel horsepower (approximately 470 crank horsepower, assuming 15% drivetrain loss) on an FA20 requires a comprehensive build. The stock engine block can handle roughly 350-400 wheel horsepower on a good tune, but reliability becomes a concern. A 400 hp goal typically demands upgraded internals, a larger turbo, and serious fuel system modifications. Below is a typical recipe used by experienced builders.

Forced Induction and Turbocharger Choice

The most common path to 400 hp is a turbocharger system. Single-turbo kits (e.g., Garrett GTX3071R or BorgWarner EFR 7064) are popular for their efficiency and spool characteristics. Twin-scroll designs help reduce lag. For a 400 hp target, a turbo in the 5858-6258 frame size is ideal, paired with a high-quality manifold and external wastegate. Kit suppliers like Full Blown Motorsports and P&L Motorsports offer proven packages.

Internal Engine Upgrades

Stock FA20 pistons and rods are cast and will bend under sustained high boost. For 400 hp, forged pistons (9.0:1 compression ratio) and forged connecting rods are mandatory. King Race bearings and ARP head studs provide additional safety. The cylinder heads benefit from upgraded valve springs and retainers to handle higher RPMs. Most builders also replace the timing chain guides and oil pump with performance units.

Fuel System and Tuning

Stock fuel injectors (4-port) cannot supply enough fuel. A full return-style fuel system with 1,000-1,300cc injectors, a larger fuel pump (AEM 340 or Walbro 525), and a flex-fuel sensor (for E85) is common. E85 offers excellent knock resistance and allows more timing advance. Tuning is absolutely critical; trust only experienced shops like Delicious Tuning or Tuned By who have extensive FA20 experience.

Supporting Modifications

  • Large front-mount intercooler (FMIC) or air-to-water intercooler
  • Full 3-inch turbo-back exhaust with high-flow catalytic converter (or catless)
  • Cold-air intake / turbo inlet tube
  • Upgraded clutch (e.g., ACT or South Bend) to handle 400+ lb-ft of torque
  • Stiffer engine and transmission mounts
  • Extra cooling: oil cooler, upgraded radiator, and possibly a dual-pass coolant expansion tank

Without these supporting mods, a 400 hp FA20 will quickly overheat, detonate, or break driveline components.

Track Performance: Where the 400hp Build Shines

On a road course or drag strip, the difference is night and day. The stock FA20 feels underpowered on long straights, while the 400 hp build transforms the car into a legitimate performance machine. Based on real-world tests from platforms like FT86 Club and independent tuners, here are typical gains.

Acceleration and Quarter-Mile Times

  • 0-60 mph: Stock 6.0s → 400 hp build: 3.4-3.6 seconds (with sticky tires)
  • Quarter-mile: Stock ~14.5s @ 96 mph → Build: 11.2-11.8s @ 122-128 mph
  • Top speed: Stock ~140 mph (limited) → Build: 165+ mph (depending on gearing)

On a road course, lap times improve by 2-4 seconds per minute of track. The higher power allows later braking zones and higher corner exit speeds. However, the stock brakes and suspension become insufficient. Most track-focused 400 hp builds include upgraded brakes (6-piston front calipers, performance pads, and better rotors), coilovers (Öhlins, KW, or Fortune Auto), and wider wheels with sticky tires (like 245/40R17 or 255/35R18).

Handling and Chassis Dynamics

The added torque upsets the car’s balance. The FA20’s soft stock suspension (especially on early models) leads to excessive body roll and wheel hop under power. A proper setup includes front and rear sway bars, subframe bushings, and a limited-slip differential (if not already equipped). The Torsen diff in the BRZ/86 can handle the power, but many opt for a clutch-type LSD for more aggressive lockup.

Heat Management and Reliability on Track

Heat is the biggest enemy of a turbocharged FA20. On a 20-minute session, oil temperatures can exceed 260°F, causing viscosity breakdown and detonation. A large oil cooler (Setrab or Mocal) with a thermostat is essential. Water temperature also rises quickly; a Mishimoto or Koyo radiator with a high-flow thermostat and electric fan upgrade is common. Many track builders add a Hoffman or Perrin dual oil cooler system. Without these, the engine will go into limp mode or suffer damage.

Street Driving: The Trade-Offs

Driving a 400 hp FA20 on the street is a different story. The raw power is thrilling, but daily usability takes a hit. Enthusiasts who drive their car to work, run errands, or deal with traffic should weigh these considerations.

Drivability and Power Delivery

The modified FA20 suffers from increased turbo lag compared to the naturally aspirated engine. Peak boost (~22-24 psi) arrives around 4,000-4,500 rpm, which is higher than the stock torque dip. Below 3,000 rpm, the car feels flat, and you might even bog off the line if the tune isn’t optimized. Modern ECUs with anti-lag or launch control can help, but they’re harsh on the drivetrain. For stop-and-go traffic, the stock engine is far more pleasant. Many 400 hp builds are paired with a manual transmission and a heavy-duty clutch that has a stiff pedal feel, making city driving tiring.

Fuel Economy and Noise

Fuel consumption drops dramatically. Stock FA20 returns around 25-28 mpg combined (depending on driving style). A 400 hp build on 93 octane will see about 16-20 mpg, and on E85 it can drop below 12 mpg under hard driving. The exhaust also becomes much louder: a full turbo-back system often produces 95-105 dB, which can be fatiguing on long trips. Some owners add a resonator or valve to quieten things down, but that adds cost.

Practical Concerns: Smog, Legality, and Insurance

Upgraded turbo systems often require removal of catalytic converters or use of high-flow cats that may not pass visual inspection in emissions-controlled states like California. Tailpipe sniffer tests also become a challenge with rich tunes. Insurance companies may deny coverage for modified engines or increase premiums significantly. Check with your provider before building. Additionally, a 400 hp FA20 demands premium fuel (93 octane minimum) or E85, which isn’t available everywhere.

Cost Analysis: Building vs. Buying

Building a reliable 400 hp FA20 isn’t cheap. Below is a realistic cost breakdown that includes common components and labor. Prices are based on current market average as of 2024-2025.

Parts List (Approximate Costs)

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  • Turbo kit (manifold, downpipe, wastegate, blow-off valve): $3,500-$5,000
  • T4/T3 turbocharger (e.g., Garrett GTX3071R): $1,500-$2,000
  • Forged pistons and rods (e.g., Manley, JE): $1,500-$2,000
  • Clutch kit (sprung hub, single or twin disc): $800-$1,500
  • Fuel system (injectors, pump, lines, regulator): $1,500-$2,500
  • Intercooler and piping: $600-$1,200
  • Oil cooler and radiator upgrade: $600-$1,200
  • Engine management and tuning (ECUtek or custom flash): $1,000-$1,500
  • Labor (engine build, install, tune): $3,000-$5,000

Total estimated cost: $14,000 to $20,000+ (excluding supporting suspension, brakes, wheels, tires, and incidental items).

Hidden Costs

  • Gauges (boost, oil pressure, AFR): $300-$600
  • Stronger axles or driveshaft (if you break stock ones): $1,000-$2,000
  • Transmission rebuild or swap (many owners blow the stock 6-speed after repeated launches): $2,000-$4,000
  • Upgraded differential (if the Torsen fails): $1,500-$3,000
  • Frequent consumables: tires (every 5-10k miles), brakes, and oil changes (more often with forced induction)
  • Potential engine failure and rebuild: $5,000-$10,000

Clearly, the total investment can exceed the car’s original value. Buying a pre-modified car might save you some money, but you inherit someone else’s problems.

Community Insights and Real-World Builds

Forums like FT86 Club and GR86.org are filled with build threads documenting 400 hp FA20 projects. One notable example is the “SBD 400X” kit, which uses a BorgWarner EFR 6758 and a fully built engine to deliver over 400 wheel horsepower on E85. Owners report reliable performance on track with proper cooling. Another popular build is the Jackson Racing turbo system combined with forged pistons and a flex-fuel tune, capable of 420 whp. However, many builders caution that the stock transmission often fails at 400+ horsepower, requiring a swap to a stronger unit (e.g., from a Subaru WRX STI or an aftermarket sequential).

Conclusion: Is 400 hp on the FA20 Worth It?

The stock FA20 offers a balanced, engaging, and reliable experience perfect for daily driving and learning performance driving. A 400 hp build transforms the car into a track-ready monster that can embarrass much more expensive machinery. But the journey is not for the faint of heart — it requires significant financial investment, technical expertise, and willingness to accept decreased daily usability. For enthusiasts who primarily track their cars and have the budget to support the build, the reward is a truly exhilarating driving experience. For those who use their car as a daily driver, the stock FA20 remains a better choice, or perhaps a milder 300 hp build that retains more drivability. Ultimately, the right choice depends on your priorities: raw performance or everyday convenience.