The Honda S2000 AP2, produced from 2004 to 2009, is a driver’s car through and through. Its high-revving 2.2-liter F22C1 engine and near-perfect 50/50 weight distribution make it a joy on twisty roads and track days alike. But after a few months of ownership, many enthusiasts find themselves wanting more than the factory 240 horsepower. The good news is that the aftermarket for this car is mature and well-supported, with a clear path from mild bolt-ons to serious forced induction builds. This guide walks you through every stage of upgrading your AP2’s power output while preserving the reliability and drivability that make the S2000 special.

Understanding the F22C1 Engine

The AP2’s F22C1 is an evolution of the earlier F20C, with a longer stroke (90.7 mm versus 84 mm) that increases displacement from 2.0 to 2.2 liters. Honda engineers also revised the VTEC engagement point and gave the AP2 a slightly flatter torque curve. Still, the engine is a high-strung, naturally aspirated four-cylinder that lives for the top end. Key specs to know:

  • Displacement: 2,157 cc
  • Compression ratio: 11.1:1
  • Redline: 8,200 RPM (fuel cut)
  • Stock horsepower: 237–240 hp at 7,800 RPM (SAE net)
  • Stock torque: 161–162 lb-ft at 6,500 RPM

The F22C1 is famously durable for a high-revving four-cylinder, with forged connecting rods and a robust valvetrain. However, the factory intake and exhaust systems are restrictive, and the stock ECU tune is conservative. Understanding these limitations is the first step in planning a build that doesn’t sacrifice reliability for power.

Setting Your Power Goals

Before spending a dollar on parts, decide what you want from the car. A weekend autocross toy, a daily driver, or a track-focused monster? While the stock 240 hp feels lively, many owners shoot for 280–350 hp through naturally aspirated (NA) upgrades, or 400–500+ hp with forced induction. Each goal dictates a different combination of parts and supporting modifications. Be honest about your budget, your mechanical skill, and whether you can tolerate a stiffer clutch or a louder exhaust for daily commuting.

Stage 1: Bolt-On Power (250–280 hp)

Cold Air Intake

A quality cold air intake like the HKS Racing Suction or PRM Aeroform replaces the restrictive factory airbox with a low-restriction filter that draws air from outside the engine bay. Expect a modest 5–8 hp gain when combined with a tune. Watch out for designs that suck hot air from behind the radiator – a proper heat shield or cold-air routing is essential.

Performance Exhaust System

AP2 exhaust systems are heavy and one of the biggest bottlenecks. A cat-back exhaust from brands like Toda Racing, GReddy, or HKS typically saves 10–15 pounds and adds 8–12 hp to the top end. For maximum flow, pair it with a test pipe (replacing the catalytic converter) or a high-flow cat. Note that removing the cat will prevent the car from passing OBD-II emissions checks in most states.

Engine Control Unit (ECU) Tuning

Tuning is the single most important upgrade for any modified S2000. The factory ECU runs lean at high RPM and conservatively retards timing to protect the catalyst. A flash tune or a standalone ECU like the Hondata FlashPro (compatible with 2005–2009 AP2s) or AEM Infinity unlocks the engine’s true potential. After a cold air intake and exhaust, a proper tune can deliver 15–20 wheel horsepower alone. Always get a custom tune on a dyno by a shop that knows F22C1s.

Stage 2: Mid-Level NA Build (280–320 hp)

Performance Headers

Long-tube headers from Toda Racing, Berk Technology, or Competition Clutch vastly improve exhaust scavenging. The F22C1’s factory exhaust manifold is a log-style cast-iron piece that chokes flow. Aftermarket headers can free up 15–20 hp at the wheels. Ceramic coating helps manage underhood heat.

High-Lift Camshafts

Once you have improved the intake and exhaust paths, the camshafts become the next restriction. Drop-in camshafts from Toda Racing Spec C or Skunk2 Stage 3 feature increased lift and duration, shifting the powerband higher. Expect gains of 15–25 hp, but you’ll also need stiffer valve springs and retainers to prevent float at high RPM. Cam timing adjustments will be critical during tuning.

Upgraded Fuel System

With more air flowing through the engine, the stock fuel injectors (310 cc/min) and fuel pump may reach their limit above 280 whp. Swap to 750–1000 cc/min injectors (e.g., Injector Dynamics or Bosch) and a Walbro 255 lph fuel pump. A return-style fuel system with a regulator is recommended for larger power targets, but the stock returnless system can handle up to about 350 whp with a rising-rate fuel pressure regulator.

Stage 3: Forced Induction (350–500+ hp)

Turbocharger Kits

Turbocharging the F22C1 transforms the car. Kits from Full-Race Motorsports, LoveFab, or Science of Speed (link to Science of Speed) are engineered for the AP2 chassis and typically include a BorgWarner or Garrett turbo, manifold, wastegate, intercooler, and charge piping. A well-tuned 300–400 whp turbo S2000 is an absolute rocket, but expect to upgrade the clutch, cooling system, and possibly the transmission mounts.

Supercharger Kits

Supercharger systems offer immediate throttle response and a linear power delivery that many drivers prefer. Centrifugal superchargers from Vortech or Rotrex (sold by LHT Performance – link to LHT Performance) can produce 350–450 whp on a stock bottom end with proper tuning. Positive-displacement superchargers (like the HKS GT2) provide even more low-end torque but are harder on the engine and require a lower compression ratio.

Engine Internals for High Boost

For reliable power above 400 whp, forged pistons (9.0:1 or 8.5:1 compression), stronger connecting rods (e.g., Carillo or Eagle), and ARP head studs become necessary. The stock F22C1 block can handle around 450 whp with a conservative tune, but the ring lands are a weak point. A sleeved block from Darton or Golden Eagle is recommended for any build over 500 whp.

Supporting Modifications for Reliability

Cooling System

Higher output means more heat. The stock aluminum radiator is adequate for mild street use, but a Koyo 36mm radiator or Mishimoto aluminum radiator with dual SPAL fans is far better for track days and heavy traffic. Also consider a Setrab oil cooler with a thermostatic sandwich plate; oil temperatures above 250°F will quickly degrade lubricity and lead to bearing failure.

Clutch and Flywheel

The factory clutch will slip around 350 whp. A Competition Clutch Stage 4 or Exedy Hyper-Twin dual-disc setup can handle 500+ horsepower while still offering a pedal feel that’s tolerable on the street. Pair it with a lightweight flywheel (e.g., Fidanza aluminum) to improve throttle response, but be prepared for a chatter at idle.

Drivetrain Upgrades

The AP2’s six-speed transmission is robust, but the differential is open from the factory. Swap in an OS Giken Super Lock LSD or a Cusco RS type LSD to put the power down effectively. Stronger axle shafts and a differential brace help prevent wheel hop under hard launches.

Suspension and Brakes

More power demands better handling. KW Variant 3 coilovers or Öhlins DFV provide adjustable damping and a lower center of gravity. Upgraded anti-roll bars, front and rear camber kits, and polyurethane bushings transform the chassis. For brakes, the AP2’s rear calipers are prone to fading under hard use – a StopTech ST-40 big brake kit front and rear with track pads and high-temp fluid will keep you confident at high speeds.

ECU Tuning and Data Logging

Regardless of power level, a proper engine management solution is non-negotiable. For NA builds, the Hondata FlashPro is the most popular choice because it’s plug-and-play, allows real-time tuning, and includes knock control. For forced induction, many tuners prefer the Hondata K-Pro (converted K-series ECU) or a standalone like Haltech Elite 2500. Data logging wideband AFR, intake air temperature, and coolant temperature is essential to catch problems before they cause damage. Many tuning shops will provide a base map and then refine it on the dyno – a full tune typically costs $500–$1,000.

Cost Considerations and Part Selection

Building a 240 hp S2000 AP2 to a 400-hp street monster isn’t cheap. A well-executed naturally aspirated Stage 2 build (intake, exhaust, headers, cams, tune, clutch) runs $5,000–$8,000 in parts and labor. A turbo or supercharger kit adds another $5,000–$12,000, plus $3,000–$5,000 for engine management and supporting mods. If you’re building a complete forged bottom-end car with a large turbo, budget $15,000–$25,000. It’s tempting to buy the cheapest parts, but poor quality intake filters, knock-off injectors, or ill-fitting headers can lead to headaches. Stick to brands with proven S2000 track records: Toda Racing, Science of Speed, LoveFab, Full-Race, and Skunk2 have years of experience on this platform.

A reliable source for build advice is the S2Ki.com forums – the community has documented countless dyno charts, failures, and success stories. Another great resource is LHT Performance (link above), which has published detailed guides on turbocharging the F22C1. Know exactly what you’re getting into before you turn a wrench, and don’t skip the tuning step – it’s what separates a car that runs like a dream from one that blows up on the highway.

Putting It All Together: A Sample Build Progression

Imagine starting with a bone-stock 2005 AP2. Month one: install a PRM intake, a Toda cat-back exhaust, and get a FlashPro tune. You’ll feel the difference on the first drive – the engine revs more freely and pulls harder to redline. Month two: add Berk headers and a 70 mm test pipe; have the tune revised. You’re now in the 260–270 whp range and losing traction on corner exit with the open diff. Month three: install an OS Giken LSD, a Competition Clutch Stage 3, and a lightweight flywheel. The car hooks up and the engine response is razor-sharp. Month six: if you want more, add Toda Spec C cams, valve springs, and retune. You’re now at 310 whp naturally aspirated – a screaming, reliable 9,000 RPM experience that still gets 25 mpg on the highway.

From there, the path to forced induction is a matter of budget and desire. A well-sorted 400 whp turbo AP2 will annihilate most modern sports cars on a back road, but it demands meticulous maintenance and a heavier wallet. There’s no shame in stopping at a mild bolt-on build – the S2000 is already a classic that rewards driver engagement and balance. The key is to build a car that matches your driving style and expectations, not the wildest forum thread you’ve read.

Final Thoughts

Taking your S2000 AP2 from stock to 240 hp (and beyond) is not just possible – it’s a well-trodden path. The aftermarket offers proven parts at every power level, and the community is generous with advice. Start with a clear plan, choose quality components, and always prioritize a professional tune. With the right approach, your AP2 will be a faster, more responsive, and more rewarding car to drive, while still offering the reliability that made it a legend. Just remember: horsepower is expensive, but a well-sorted S2000 is priceless.