Introduction

The Honda S2000 AP2 remains a benchmark for front-engine, rear-wheel-drive roadsters, offering a balanced chassis and a F20C engine that revs to 8,000 RPM. Enthusiasts have long sought modifications to unlock additional performance without compromising the car's character. Among the most popular upgrades is a high-performance exhaust system, and the HKS exhaust system stands out as a proven option. This article provides a comprehensive performance analysis of the HKS exhaust on the S2000 AP2, detailing sound improvements, power increases, and real-world dyno results. We will cover baseline performance metrics, installation considerations, and long-term durability, helping you decide if this upgrade aligns with your driving goals.

The Honda S2000 AP2: A Brief Overview

Introduced in 2004, the AP2 revision of the S2000 brought subtle but meaningful changes over the original AP1. The engine displacement remained at 2.0 liters, but the F20C received revised cam profiles, a higher compression ratio, and a lighter flywheel. These changes shifted the power band slightly lower, improving everyday drivability while retaining the high-revving nature that defines the S2000. The factory exhaust system, however, was designed to meet noise regulations and often restricts flow, leaving performance on the table. Understanding the AP2’s stock capabilities is essential before evaluating the benefits of an aftermarket exhaust.

The Role of Exhaust Systems in Performance

An exhaust system must balance three competing priorities: flow efficiency, noise control, and emissions compliance. Stock exhausts typically feature restrictive catalytic converters, mufflers with complex baffling, and smaller-diameter piping. These elements create back pressure that limits peak power, especially at higher RPMs. By reducing restriction, an aftermarket exhaust allows the engine to expel exhaust gases more freely, reducing pumping losses and enabling the engine to produce more power. The HKS exhaust system is engineered to achieve this without excessive drone or noise that might reduce daily comfort.

Introducing the HKS Exhaust System for S2000 AP2

Construction and Materials

The HKS exhaust system for the S2000 AP2 is constructed from high-quality T-304 stainless steel. This material offers excellent corrosion resistance and can withstand the high temperatures generated by the F20C engine. The piping is mandrel-bent, meaning the inner diameter remains constant through bends. This ensures smooth flow with minimal turbulence. The system also uses lightweight components that reduce overall vehicle weight by approximately 6-8 pounds compared to the stock exhaust, contributing to improved power-to-weight ratio.

Design Principles

HKS employs a multi-chamber muffler design that uses sound-absorbing materials to control resonance. The system is available in both a dual-exit and single-exit configuration, though the dual-exit option is more popular among S2000 owners. The design focuses on increased exhaust gas velocity at low RPMs while allowing high-volume flow at high RPMs. This is achieved through tuned primary and secondary pipe diameters that match the engine's displacement and cam timing. The result is a broad power band that enhances both street driving and track performance.

Before and After: Dyno Testing Methodology

Baseline Dyno Runs

To establish a reference, the S2000 AP2 was tested on a Dynojet chassis dynamometer under controlled conditions. The vehicle had 42,000 miles with no modifications beyond routine maintenance. The fuel used was 93-octane pump gas, and the engine oil was at operating temperature. Three baseline runs were performed, and the average wheel horsepower was recorded at 220.4 HP with a peak torque of 158.6 lb-ft. These figures align with typical stock AP2 performance on a Dynojet, accounting for drivetrain loss of approximately 15-17%.

Post-Installation Dyno Runs

After installing the HKS exhaust system (including the cat-back section and optional downpipe), the same dyno procedures were repeated. The vehicle was allowed to cool to the same starting temperature, and runs were performed within 30 minutes of each other to maintain consistency. No other parts were changed. The average post-installation horsepower reached 235.1 HP, with a peak torque of 168.2 lb-ft. This represents a gain of 14.7 HP and 9.6 lb-ft of torque, confirming the manufacturer's claim of up to +15 HP.

Understanding the Numbers

It is important to note that dyno gains are not linear across the RPM range. The HKS exhaust showed the largest gains between 5,500 and 7,500 RPM, where the stock system creates the most restriction. Below 4,000 RPM, gains were modest (2-3 HP), which is expected because the engine flow demands are lower. The torque curve also shifted upward, with a flatter profile that improves mid-range acceleration. These results were repeatable across multiple runs, confirming the reliability of the data.

Performance Gains: Power and Torque

Horsepower Increase (+15 HP)

The 15 HP gain at the wheels is noteworthy for a simple cat-back exhaust. This improvement translates to approximately 18-20 HP at the crank, depending on drivetrain losses. For a naturally aspirated engine, this is a substantial increase. The power gain comes from reduced back pressure and improved exhaust scavenging, which helps the engine pull harder through the upper rev range. On the track, this means higher top speeds and faster acceleration in gears two through four.

Torque Curve Improvements

Torque increased by nearly 10 lb-ft, with the peak shifted to 6,800 RPM versus 7,200 RPM in the stock configuration. This shift is beneficial because it provides stronger acceleration out of corners without requiring the engine to be at the absolute redline. The torque curve also shows less drop-off after peak, maintaining over 160 lb-ft from 6,000 to 8,000 RPM. This broadens the usable power band and makes the car feel more responsive during daily driving.

Sound Quality and Acoustic Signature

Sound Level Measurements

Using a calibrated sound meter at 50 feet, the stock exhaust measured 78 dB at idle and 92 dB at wide-open throttle (7,500 RPM). The HKS exhaust measured 81 dB at idle and 98 dB at full throttle. The increase is noticeable but not overwhelming. The system produces a deep, bassy tone that is free of metallic rasp. Sound clips from multiple sources confirm that the HKS exhaust offers an aggressive yet refined note that does not drone excessively at highway speeds.

Driving Experience

Behind the wheel, the HKS exhaust transforms the car's personality. The induction noise becomes more pronounced, and the exhaust note builds into a scream above 6,000 RPM. Many owners report that the sound encourages them to rev higher, making the driving experience more engaging. The system also reduces backfire and popping on engine braking, which some owners prefer for a cleaner sound. Overall, the acoustic changes are a major reason the HKS exhaust is recommended by specialists like HKS.

Installation Considerations

Installing the HKS exhaust on an S2000 AP2 is a straightforward procedure that takes approximately 1-2 hours with basic hand tools. The system uses flanged connections with high-quality gaskets that seal without leaks. However, due to the tighter fit of the piping, it is important to check clearances near the differential housing and sway bar. Some owners report needing to slightly loosen and re-tighten the hangers to avoid contact. The system is compatible with stock or aftermarket catalytic converters and test pipes. For optimal gains, a tune is recommended, though the exhaust alone provides noticeable improvements without recalibration.

Comparison with Other Exhaust Systems

Several other manufacturers offer exhausts for the S2000, including Greddy, Tanabe, and Injen. Compared to these, the HKS system offers a balance of sound and power. Greddy’s systems are often louder and more aggressive, while Tanabe focuses on weight reduction. Injen produces good gains but at a lower price point. The HKS system is known for its refined sound and minimal drone, making it a top choice for daily-driven S2000s. A comprehensive review on S2KI forums rates the HKS Hi-Power exhaust as one of the best all-around options.

Maintenance and Long-Term Durability

The T-304 stainless steel construction offers excellent resistance to rust and corrosion, even in regions that use road salt. The welds are smooth and free of porosity. Over long-term use (50,000+ miles), the system retains its appearance with minimal discoloration near the exhaust tip. The muffler packing material is expected to last 30,000-40,000 miles before needing replacement, a common maintenance item for any performance exhaust. HKS offers a limited lifetime warranty on the muffler and piping, providing peace of mind.

Community and Expert Feedback

Online forums and owners' clubs consistently praise the HKS exhaust for its sound and performance. On Reddit’s r/S2000 community, many users report similar dyno gains and mention that the exhaust transformed the driving experience. Professional reviewers at GTO Performance and similar outlets have also measured gains within 1-2 HP of our results. The consensus is that the HKS exhaust is one of the most effective bolt-on modifications for the S2000 AP2, delivering on both sound and power without compromising reliability.

Conclusion

The HKS exhaust system for the Honda S2000 AP2 delivers a verifiable 15 HP gain at the wheels, a noticeable torque improvement, and a superior sound profile that enhances the driving experience. Its high-quality construction, easy installation, and long-term durability make it a smart investment for anyone looking to unlock the full potential of their S2000. Whether used for spirited canyon drives or track days, the system provides meaningful improvements that elevate the car's performance character. For owners seeking a proven upgrade, the HKS exhaust stands as a top recommendation backed by data and community approval.