Understanding the F20C Engine and Its Quirks

The Honda S2000 AP1 is powered by the legendary F20C engine, a naturally aspirated 2.0-liter inline-four that revs to a dizzying 9,000 rpm. Its high specific output and VTEC variable valve timing make it one of the most revered engines of its era. However, the very characteristics that make the F20C thrilling also give rise to common performance issues as the car ages. Owners must understand that many of these problems stem from heat management, component wear, and factory compromises made for cost and emissions. By addressing these weaknesses with purpose-built aftermarket solutions, you can restore—and even improve—the car's original performance envelope. This article systematically breaks down each frequent problem and details the parts, products, and procedures that experienced owners and shops recommend.

Engine Overheating: Causes and Cures

Engine overheating is one of the most reported issues on the S2000 AP1, especially during spirited driving or track days. The stock radiator, while adequate for street use, struggles to shed heat during sustained high-rpm operation. Contributing factors include a failing thermostat that sticks closed, clogged coolant passages after years of neglect, or an original radiator with plastic end tanks that develop cracks. Overheating not only risks head gasket failure but also triggers the ECU to pull timing, robbing you of power just when you need it most.

Aftermarket Radiator Upgrades

The first line of defense is a larger-capacity radiator. Many owners replace the OEM unit with an all-aluminum radiator from Koyo or Mishimoto. The Koyo VH072558 is a popular direct-fit unit that increases core thickness by nearly 40%, dramatically improving heat rejection. Mishimoto offers a CNC-machined radiator cap with a higher pressure rating (1.3 bar vs. stock 1.1) to raise the boiling point of your coolant. If you frequently drive in hot climates or at the track, consider a Mishimoto fan shroud kit that includes dual high-flow fans wired to run simultaneously. For those wanting maximum cooling, a PWR radiator with integrated oil cooler can be used, though it may require slight modifications to the bumper support.

Thermostat and Coolant Management

Replace the factory thermostat with a low-temperature unit (e.g., Mugen 68°C or Spoon 70°C) to allow coolant to circulate earlier. However, be aware that too low a thermostat can prevent the engine from reaching operating temperature in cold weather, causing rich running and increased fuel dilution. A balanced choice is a Mishimoto 74°C thermostat. Flush the entire cooling system with distilled water and Honda Type 2 coolant or a high-quality ethylene glycol blend. Pay attention to the coolant hoses—replace them with silicone hoses from Samco or Mishimoto to prevent burst failures at the water pump neck. Finally, upgrade the water pump to a Gates Racing or OEM replacement with a metal impeller if your car still has the original plastic version.

For more information on cooling system diagnostics, the S2KI forum has extensive threads with step-by-step guides.

Restoring Throttle Response

The AP1 uses a cable-driven throttle body, not drive-by-wire. A lazy or sticking throttle can make the car feel sluggish, especially when trying to rev-match downshifts. The most common cause is carbon buildup on the throttle plate and inside the bore. Over time, this gunk restricts airflow and causes the plate to stick when you first press the pedal. Another cause is a worn accelerator pedal assembly—the cable can stretch or the pedal return spring weakens.

Cleaning and Replacing the Throttle Body

Remove the intake duct and visually inspect the throttle body. Use a dedicated throttle body cleaner (not carb cleaner, which can damage the Teflon coating) and a soft brush to scrub away carbon. Manually open the plate with your fingers while cleaning. After reassembly, perform a TPS (throttle position sensor) voltage reset procedure: with the ignition on, slowly open and close the throttle, then cycle the key. If cleaning doesn't restore crisp response, consider an oversized throttle body, such as the Skunk2 Pro Series 70mm unit. This requires port matching to the intake manifold or using a spacer. Pair it with a Skunk2 Ultra Street intake manifold for maximum gains, though even a cleaned stock unit with a high-flow intake (like the AEM V2) will improve throttle feel.

Upgraded Accelerator Pedal Assembly

If the pedal itself feels sloppy, replace the entire assembly with an aftermarket unit from Hardtopguy or a used OEM part in better condition. Some owners install a throttle pedal extension to make heel-and-toe shifts easier, which indirectly improves perceived response. An alternative is to adjust the cable tension—locate the adjustment nut at the throttle body bracket and tighten it just enough to remove slack without holding the throttle open.

Taming Excessive Engine Vibrations

As the rubber in the OEM engine mounts ages, it hardens and cracks, allowing the engine to move excessively under load. This leads to vibrations felt through the steering wheel, floor pan, and even the gear shifter. A worn rear mount is particularly noticeable when you shift into first gear or reverse. Excessive movement also misaligns the drivetrain, placing stress on the transmission case and axles.

Aftermarket Engine Mounts

The most effective remedy is replacing the three engine mounts with polyurethane or billet aluminum units. Hasport Performance offers mount sets in various durometers: 70A (street-legal, mild vibration increase), 80A (track-friendly, noticeable at idle), and 95A (race-only, harsh). For a daily-driven S2000, the 70A or 80A compound from Innovative Motor Mounts is recommended. These mounts drastically reduce engine movement, improve shift feel, and eliminate the clunk when engaging the clutch. Install them with blue Loctite on the mounting bolts and torque to factory specifications (54 Nm for the main mounts).

Additional Vibration Dampers

If you still feel residual vibrations, install a polyurethane harmonic damper on the crankshaft pulley (unnecessary on the F20C which has a good harmonic balancer from the factory), or a vibration damper bracket on the transmission (e.g., the Spoon Sports transmission mount stopper). Also check the condition of the rear differential mounts—worn diff mounts can transfer vibration into the cabin. Replace with polyurethane units from Energy Suspension or a full kit from Powertrain Solutions.

Banishing Brake Fade for Track Days

The AP1's braking system is adequate for street driving but quickly fades during repeated hard stops on backroads or at the track. Brake fade occurs when the pads, rotors, and fluid exceed their thermal limits. The stock brake pads are prone to glazing, and the single-piston calipers struggle to dissipate heat. Upgrading pads and fluid is the most cost-effective way to eliminate fade.

Performance Brake Pads & Rotors

For a dual-purpose car that sees occasional track days, choose a compound like Carbotech XP10 or Hawk HP Plus. These pads offer a high friction coefficient from cold and can withstand significant heat without fading. Pair them with drilled or slotted rotors to increase bite and help outgas pad material. StopTech slotted rotors are a popular choice—they resist cracking better than drilled rotors. For dedicated track cars, consider a full big brake kit (BBK) from StopTech or Wilwood with 4-piston calipers and larger rotors (320 mm front, 290 mm rear). This kit dramatically improves stopping power and heat management.

High-Performance Brake Fluid

Brake fluid absorbs moisture over time, lowering its boiling point. Use Motul RBF 600 or Castrol SRF—both have dry boiling points above 310°C. Flush the entire system every 12 months or after every three track events. Also install brake cooling ducts that route air from the front bumper to the rotors. Rennsport or DIY backing plate mods (removing the dust shields and adding NACA ducts) can reduce rotor temperatures by 50–100°C.

Learn more about brake upgrades from StopTech's technical guides.

Improving Transmission Feel

The AP1's six-speed manual transmission is generally robust, but owners frequently complain about a stubborn 2nd gear grind when shifting quickly at high rpm. This is caused by worn synchronizers, insufficient lubrication, or a misadjusted clutch pedal. Difficulty shifting into reverse or a notchy feel across all gears also indicates worn linkage or old fluid.

Synchronizer and Fluid Solutions

Before rebuilding the transmission, try a high-quality aftermarket gear oil. GM Synchromesh (part number 88900399) or Amsoil Manual Synchromesh is known to reduce the 2nd gear grind in many S2000s. Drain the old fluid and refill with 2.1 quarts. If the grind persists, install Carbon Synchros from Synchrotech—these provide a higher coefficient of friction and last longer than brass synchros. This requires transmission disassembly, so it's best left to a specialist.

Short-Throw Shifters and Clutch Upgrades

A short-throw shifter reduces the lever travel and tightens the gate, making shifts quicker and more precise. The Buddy Club Short Shifter and KMiata (K-Tuned) S2000 shifter are popular choices. They use spherical bearings instead of the stock rubber bushings, resulting in a direct mechanical feel. Pair the shifter with polyurethane shifter base bushings from Bryan Thompson or Energy Suspension.

Clutch engagement problems can also cause grinding. Replace the original clutch master cylinder and slave cylinder with KMiata CMC/SC kit (designed to correct the bore sizing and provide more consistent pedal feel). Upgrade the clutch disc to a Exedy Stage 1 Organic or ACT Heavy Duty unit—these hold more torque and reduce the tendency of the disc to "float" at high rpm, which can lead to missed shifts.

Other Performance Bottlenecks

Beyond the five main problems listed above, several other areas limit AP1 performance. Intake and exhaust restrictions rob the F20C of top-end horsepower, while the stock ECU tune is conservative. Addressing these unlocks the engine's true potential.

Intake Systems

The stock airbox is restrictive at high rpm, especially after installing a less restrictive exhaust. Install a high-flow intake such as the AEM V2 or Mishimoto Performance Intake. Both feature larger filter surfaces and smooth intake tubes that reduce turbulence. The Fujita F5 intake is another proven option. If you want to keep the engine bay cleaner, the Ballade Sports carbon fiber intake box with a larger K&N filter is effective.

Exhaust Systems

Replace the factory exhaust manifold (which has restrictive cast iron) with a set of long-tube headers from Toda Racing, Mugen, or Berk Technology. These headers improve scavenging and increase peak power by 10–15 hp. Pair them with a test pipe or high-flow catalytic converter (e.g., MagnaFlow) and a cat-back exhaust such as the HKS Hi-Power or Greddy Supreme SP. Keep in mind that the AP1's exhaust note is iconic; choose a system with a Helmholtz resonator or baffles to avoid drone.

ECU Tuning

The stock ECU is locked, but you can reprogram it using Hondata FlashPro. This allows you to adjust fuel maps, ignition timing, VTEC engagement point, and rev limiter. A custom tune by a professional (like Church Automotive Testing or HTUNED) can safely extract 20–30 additional horsepower from a bolt-on setup. FlashPro also includes datalogging capabilities to monitor knock and AFR in real time.

For a comprehensive tuning guide, visit Hondata's official site.

Conclusion

Owning a Honda S2000 AP1 means embracing a car that rewards maintenance and thoughtful upgrades. The common problems of overheating, poor throttle response, engine vibrations, brake fade, and transmission issues are not flaws of the platform but opportunities to tailor the car to your driving style. By selecting aftermarket solutions such as upgraded radiators, polyurethane mounts, heavy-duty brake components, and quality shifters, you can preserve the car's legendary character while eliminating its weaknesses. Approach each fix methodically—start with the most impactful (cooling and brakes) before moving to driveline and engine management. With the right combination of parts and a little effort, your AP1 will remain a joy to drive for thousands of miles to come.