Introduction: Unlocking the F22C’s Hidden Potential

The Honda S2000 AP2, produced from 2004 to 2009, is the refined evolution of a modern icon. Its 2.2-liter F22C engine delivers 237 horsepower at 7,800 rpm and 162 lb-ft of torque—more low-end grunt than the earlier F20C, but still a high-strung four-cylinder that rewards every rpm. Enthusiasts seeking additional thrills often turn to naturally aspirated bolt-on modifications before considering forced induction. Two of the most popular entry-level upgrades are lightweight pulleys and a free-flowing exhaust system. When combined, these parts can liberate 15–30 wheel horsepower, sharpen throttle response, and shed significant weight without sacrificing daily drivability. This article provides a comprehensive breakdown of what to expect from pulley and exhaust upgrades on the AP2, including technical details, dyno-verified gains, installation considerations, and a no-nonsense look at the costs involved.

Pulley Upgrades: Reducing Rotating Mass

How Pulleys Affect Engine Performance

The F22C’s accessory drive system includes a crankshaft pulley (harmonic damper), alternator pulley, water pump pulley, and sometimes an idler pulley. The stock crankshaft pulley is a heavy, rubber-damped unit weighing around 4–5 pounds. Its mass absorbs vibrations but also adds rotational inertia, which saps power as the engine revs. Lightweight aftermarket pulleys—typically made from billet aluminum or chromoly steel—can weigh as little as 1–1.5 pounds for the crank pulley and even less for the accessories. By reducing the weight of the rotating assembly, the engine expends less energy spinning those components, freeing up horsepower that can reach the wheels.

Contrary to some claims, lightweight pulleys do not directly increase the engine’s torque output. Instead, they reduce parasitic losses, meaning more of the power the engine produces actually makes it to the drivetrain. Throttle response improves noticeably because the engine can accelerate and decelerate faster without the heavy pulley’s inertia fighting against it. On the AP2, typical dyno results show gains of 5–10 wheel horsepower from a crank pulley alone, and up to 12–15 wheel horsepower when paired with lightweight alternator and water pump pulleys.

Specific Products and Considerations

Popular options for the AP2 include the Science of Speed underdrive pulley kit and the Lightweight Technologies (LHT) performance pulley set. The Science of Speed kit underdrives the alternator and water pump slightly, reducing drag at high rpm while still maintaining proper charging at idle. Some purists prefer non-underdrive pulleys to avoid any effect on accessory speed. It’s worth noting that underdrive pulleys may cause lower alternator output at sustained low-rpm cruising (e.g., in heavy traffic), but this is rarely an issue in street use. For track cars, a non-underdrive set is often recommended to keep cooling and electrical systems running at full capacity.

Installation is straightforward for a DIYer with basic hand tools, but the crankshaft bolt is torqued to 130 lb-ft and requires a special tool to hold the pulley. Many owners opt to replace the main pulley bolt with a new OEM piece (Part No. 90013-PR3-A00) and use thread-locker during reinstallation. Expect to spend 2–3 hours on the job if you’re experienced. Professional installation typically adds $150–$300.

Potential Risks

The stock harmonic damper is designed to dampen crankshaft vibrations at certain frequencies. Replacing it with a solid aluminum pulley can, in theory, increase harmonic stress on the crankshaft and bearings. However, for street-driven S2000s and even many track cars, this has proven to be a non-issue in the community; the F22C’s crank is robust enough to handle the change. Nevertheless, some owners retain the stock crank pulley and only upgrade the accessory pulleys to avoid any concerns.

Exhaust System Upgrades: Letting the F22C Breathe

Why the Stock System Restricts Power

The AP2’s factory exhaust is a compromise between noise, emissions, and cost. It features a heavy cast-iron exhaust manifold (header) that splits into two separate pipes before merging into a restrictive catalytic converter and a muffler system with moderate flow. The exhaust manifold is the biggest bottleneck; its unequal-length runners cause exhaust pulses to interfere with each other, limiting scavenging and high-rpm power. Even a free-flowing cat-back exhaust alone will yield only modest gains—typically 5–8 whp—because the restrictive headers remain in place. To maximize gains, the exhaust system should be upgraded in stages: header (or header + test pipe), then cat-back.

Header Upgrade

Aftermarket headers for the AP2 are almost always equal-length designs, which improve exhaust pulse timing and increase scavenging. This allows the engine to expel spent gases more efficiently and draw in a fresh air-fuel charge, directly boosting torque and horsepower across the mid-to-high rpm range. Top-of-the-line options include Toda Racing’s equal-length header, the Berk Technology header, and the Injen Gen2 system. These headers are typically made from T304 stainless steel and come with or without a catalytic converter. Gains from an aftermarket header alone range from 8–12 whp on a stock ECU.

If you choose a header without a catalytic converter (a “test pipe” setup), you can gain another 3–5 whp but will trigger a check engine light (CEL) due to the missing post-cat O2 sensor. This can be addressed with an O2 sensor spacer, or better yet, a tune (see below). Note that removing the catalytic converter is illegal on public roads in many jurisdictions and will cause the car to fail emissions testing.

Test Pipe / High-Flow Cat

A test pipe (straight pipe replacing the catalytic converter) or a high-flow catalytic converter reduces backpressure further. High-flow cats from companies like Random Technology or GReddy flow almost as well as a test pipe while still providing emissions legality. Gains of 2–4 whp are typical on a tuned car. Expect to pay $100–$300 for a test pipe and $300–$600 for a high-flow cat.

Cat-Back Exhaust

The cat-back system (from the catalytic converter rearward) affects sound more than power on a stock or lightly modified engine. A well-designed cat-back can add 5–8 whp over the restrictive stock muffler. Favorites in the S2000 community include the HKS Carbon Ti, the Fujitsubo Legalis R, the GReddy Supreme SP, and the AP2 Anxiety exclamation point exhaust for those seeking a distinctive tone. Many cat-backs weigh 10–15 pounds less than the factory unit, contributing to overall weight reduction. Installation is a straightforward bolt-on job that takes about an hour.

Dyno Results: Typical Gains from Full Exhaust

An AP2 with a quality equal-length header, test pipe, and cat-back exhaust typically sees gains of 18–25 wheel horsepower compared to a completely stock car, as verified on multiple independent dyno sheets. For example, a popular S2KI.com thread compiling dyno results shows a 2006 AP2 gaining 22 whp and 12 lb-ft of torque from a Toda header, HFC, and GReddy cat-back. The peak power migrated from 7,800 rpm to about 8,200 rpm, with the engine still pulling hard to the 8,500 rpm fuel cut.

Combining Pulleys and Exhaust: Synergistic Gains

When lightweight pulleys are added to a car already equipped with a free-flowing exhaust, the gains are additive but also synergistic: the engine revs faster (thanks to less rotating inertia) and breathes more freely (thanks to the exhaust), so it reaches peak power more quickly and sustains it longer. Expect combined gains of 20–35 wheel horsepower over a stock AP2. A well-known independent dyno test published by Science of Speed shows a car with their underdrive pulley set, a Berk header, and a Mugen cat-back gaining 28 whp and 18 lb-ft of torque over stock. That’s a noticeable seat-of-the-pants difference: the car pulls harder from 5,000 rpm onward and feels significantly quicker through the gears.

Because the F22C is already a strong base, these mods bring the power-to-weight ratio closer to cars like the Porsche Cayman S, without the cost or complexity of a supercharger. The trade-off is that peak power still remains modest by modern standards — around 265–275 wheel horsepower on a well-tuned car — but the driving experience is transformed by the sharper response and the glorious sound of a high-revving naturally aspirated four-cylinder.

Tuning: The Missing Piece for Maximum Gains

Stock ECU tuning on the AP2 is conservative, with fuel and ignition maps designed for 91 octane pump gas and a wide safety margin. After installing pulleys and an exhaust, the engine will be running slightly leaner at the top end due to increased volumetric efficiency. While the stock ECU can compensate to some extent via its long-term fuel trims, it rarely provides optimal ignition timing or air-fuel ratios for maximum power. That’s where a reflash or standalone ECU comes in.

The Hondata FlashPro is the go-to tuning solution for the S2000 AP2. It allows a tuner to adjust fuel maps, ignition timing, VTEC engagement point, and rev limiter (safe to 8,700 rpm with valve springs). A custom tune for a car with pulleys and exhaust typically adds another 5–10 whp over the bolt-on parts alone, while also smoothing out the power curve and improving drivability. Expect to pay $695 for the FlashPro unit plus $400–$600 for a professional dyno tune.

Without a tune, you will still see most of the gains from the hardware, but you leave a small but noticeable amount of power on the table. Many owners drive for years with just the bolt-ons and remain satisfied, but for those chasing every last horsepower, a tune is strongly recommended.

Cost Considerations: Building a Budget and Sticking to It

Modifying any car requires a clear budget. Below is a realistic breakdown of costs for a complete pulley-and-exhaust upgrade on an S2000 AP2. Prices are in USD and reflect mid-level aftermarket parts; premium brands will cost more.

Modification Typical Cost Notes
Lightweight pulley set (crank + 2 accessory) $200 – $600 Most sets include alternator & water pump pulleys; crank pulley sold separately sometimes.
Equal-length header $600 – $1,500 Toda, Berk, Injen, etc. Stainless steel. Includes gaskets.
High-flow cat or test pipe $100 – $600 HFC for street legality, test pipe for max flow.
Cat-back exhaust $500 – $2,000 Titanium or stainless. Weight saving varies.
Installation (professional) $300 – $600 For header + cat-back + pulleys combined. DIY saves this.
ECU reflash/FlashPro + tune $1,000 – $1,300 If you want max power. Not strictly required but recommended.
Total (without tune) $1,700 – $4,700 Wide range due to brand choices.
Total (with tune) $2,700 – $6,000 Includes all parts, install, and tuning.

It’s easy to spend $4,000 or more if you choose top-shelf components and professional installation. However, a budget-minded approach using a set of used pulleys (e.g., LHT set for $250), a Berk header (around $700), a used cat-back ($400), and DIY installation can keep the total under $1,500 while still netting substantial gains. The key is to prioritize the parts that give the biggest power-per-dollar: the header is the most impactful single mod, followed by pulleys, then cat-back.

Conclusion: Realistic Expectations for the AP2 Enthusiast

Upgrading the pulleys and exhaust on a Honda S2000 AP2 is one of the most rewarding naturally aspirated modification paths. The combination of reduced rotating mass and improved engine breathing yields a tangible increase in power—typically 20–35 wheel horsepower—along with sharper throttle response, a more exhilarating sound, and a lighter curb weight. The total cost, whether you DIY or pay a shop, is modest compared to forced induction, making this an accessible entry point for owners who want to extract more from the legendary F22C.

To get the best results, plan your modifications as a complete system: choose a header and cat-back that are known to work well together, add underdrive or lightweight pulleys, and consider a FlashPro tune if your budget allows. Always research parts thoroughly on forums like S2KI.com and consult with a reputable shop or tuner who has experience with the AP2. With the right combination, your S2000 will feel more alive than ever—an authentic return on investment for one of the most celebrated sports cars of the 2000s.