Installing a lightweight flywheel on your Scion FR‑S is one of the most effective bolt‑on modifications for sharpening throttle response and improving acceleration. By reducing rotational mass, this upgrade allows the engine to rev more freely, delivering quicker spool and a more engaging driving experience. This comprehensive guide covers everything from understanding the flywheel’s role to detailed installation steps, torque specifications, and performance trade‑offs. Whether you’re a seasoned DIY mechanic or a dedicated enthusiast, you’ll find the information needed to complete the job safely and effectively.

Understanding the Lightweight Flywheel Upgrade

The flywheel is a heavy metal disc mounted between the engine and the clutch. Its primary function is to store rotational energy to smooth out engine pulses and provide inertia for starts and stops. A factory flywheel is intentionally heavy to improve drivability, reduce stalling, and dampen vibrations. By replacing it with a lightweight version—typically 8–12 pounds versus the stock 18–20 pounds—you reduce the rotational inertia that the engine must overcome during acceleration.

The result is faster rev‑up and rev‑down, making the engine feel eager and responsive. This is especially noticeable in the Scion FR‑S (and its siblings, the Subaru BRZ and Toyota 86) because the naturally aspirated FA20 engine benefits from any reduction in parasitic drag. However, lighter flywheels can also make the car slightly more difficult to start from a stop and may increase gear rattle at idle. For most performance‑oriented drivers, these trade‑offs are well worth the gains in throttle response and acceleration times.

Tools and Parts Required

Before starting, gather all necessary components and tools. In addition to the lightweight flywheel itself, you’ll need high‑quality fasteners and specialty items to ensure a smooth process.

Parts

  • Lightweight flywheel (e.g., Fidanza, ACT, or Exedy)
  • New flywheel bolts (stock or ARP) – always replace these
  • Clutch disc and pressure plate (optional but recommended while transmission is out)
  • Transmission oil (75W‑90 GL‑4) – you’ll lose some during removal
  • Engine oil and filter if you’re performing a simultaneous service

Tools

  • Socket set (metric: 10mm, 12mm, 14mm, 17mm, 19mm)
  • Torque wrench (ft‑lbs and in‑lbs capabilities)
  • Flywheel lock tool (or a large screwdriver as a backup)
  • Floor jack and jack stands
  • Transmission jack or a sturdy helper
  • Breaker bar for stubborn bolts
  • Pry bar (for separating engine and transmission)
  • Safety glasses and mechanic’s gloves
  • Thread locker (medium strength, e.g., Loctite 242)
  • Brake cleaner for cleaning surfaces

Safety Precautions

Working under a vehicle involves serious risks. Park the FR‑S on a level concrete surface and chock the rear wheels. Disconnect the negative battery terminal to prevent accidental starter engagement. Use jack stands rated for the vehicle’s weight and never rely solely on a hydraulic jack. Allow the engine and exhaust system to cool completely before beginning. Wear safety glasses during all steps where debris, oil, or metal particles could fly.

Step‑by‑Step Installation Guide

The process requires removing the transmission to access the flywheel. Expect a full day of work if you are doing this for the first time. Work methodically and keep all removed parts organized.

Preparation and Disassembly

Start by ensuring the vehicle is securely lifted on four jack stands. Remove the negative battery terminal. Drain the transmission oil to avoid spillage when the axles are removed. Next, disconnect the driveshaft from the rear differential by removing the four bolts. Slide the driveshaft toward the transmission and support it with a strap or zip tie. Remove the starter motor (two bolts and the electrical connector). Unbolt the transmission mount from the crossmember and support the transmission with a transmission jack.

Removing the Transmission

Remove the front wheels for easier access to the suspension components. Detach the stabilizer bar links and unbolt the lower control arm to free the axles. Slide the axles out of the transmission output shafts and hang them out of the way. Label all electrical connectors and remove the clutch slave cylinder (two bolts). Disconnect the reverse light switch and any remaining harnesses. Lower the transmission jack slightly and unbolt the bellhousing from the engine block. Carefully wiggle the transmission off the dowel pins and lower it to the floor. You may need a pry bar to separate the bellhousing if it is stuck.

Removing the Old Flywheel

With the transmission out, you’ll see the pressure plate and flywheel. First, remove the pressure plate and clutch disc by unbolting the pressure plate in a crisscross pattern. Once the clutch is off, use a flywheel lock tool to prevent the crankshaft from rotating. Unbolt the flywheel, again in a crisscross pattern to avoid warping. Note that the factory flywheel bolts are often thread‑locked from the factory; use a breaker bar. Remove the flywheel and inspect the crankshaft flange for any burrs or debris. Clean the mating surface with brake cleaner.

Installing the Lightweight Flywheel

Place the new lightweight flywheel onto the crankshaft locating dowel. Ensure it sits flush. If the flywheel does not slide on easily, do not force it; check for alignment issues. Install new flywheel bolts (never reuse old ones) and apply a drop of medium thread locker to each. Tighten the bolts in a crisscross pattern to the manufacturer’s specified torque. For most lightweight flywheels on the FA20, torque is between 55 and 65 ft‑lbs. Verify the spec with your flywheel’s instructions. After torquing, rotate the crankshaft 360° by hand to confirm the flywheel spins freely and doesn’t rub on anything.

If you are replacing the clutch as well, now is the time to install a new pilot bearing (if included), then the clutch disc and pressure plate. Use a clutch alignment tool to center the disc. Torque the pressure plate bolts in stages following the service manual.

Reassembling the Transmission

Before lifting the transmission back into place, inspect the input shaft splines and apply a thin layer of high‑temperature grease. Also check the throwout bearing and replace if worn. Raise the transmission on the jack and align it with the engine. Slide it onto the dowel pins carefully; do not force it. If it stops short, check that the input shaft splines are engaging the clutch disc. Once fully seated, install the bellhousing bolts (hand‑tight initially) then torque them to spec in a cross pattern. Reconnect all electrical connectors, the slave cylinder, axles, suspension components, starter, driveshaft, and transmission mount. Refill the transmission with fresh oil.

Final Checks and Test Drive

Reconnect the battery, start the engine, and let it idle for a couple of minutes. Listen for any unusual noises from the transmission area. A slight gear rattle is normal with a lightweight flywheel. Check for oil or transmission fluid leaks. Perform a careful test drive, gradually working through the gears. You will immediately notice faster engine revs and a more responsive throttle. Practice smooth clutch engagement; the lighter flywheel requires a slightly different technique for seamless starts. If you experience excessive chatter or vibration, double‑check all torque values and ensure the flywheel and clutch are properly centered.

Performance Gains and Considerations

The primary gains from a lightweight flywheel are improved throttle response and quicker acceleration, especially in lower gears. By reducing rotating mass by roughly 8–10 pounds, the engine can accelerate faster on the dyno and on the street. Quarter‑mile times can improve by up to 0.2–0.3 seconds, with a more noticeable difference during spirited corner exits. The engine also decelerates faster when you lift off the gas, which can help with rev‑matched downshifts.

On the downside, the car becomes slightly harder to drive smoothly in stop‑and‑go traffic. The revs drop more quickly, so you need to shift faster. Some drivers also report increased transmission gear rattle at idle and low speeds, which is a normal consequence of reduced flywheel damping. If you plan to add forced induction later, a lightweight flywheel may not be ideal due to the need for more rotational mass to spool the turbo; for supercharged setups it can still work well. Consider pairing the flywheel with a stage 1 or 2 clutch that still offers streetable engagement.

Tuning and Complementary Upgrades

To fully exploit the lighter flywheel, consider a professional ECU tune. The factory ECU may not be optimized for the reduced rotational inertia, and a tune can improve throttle mapping, ignition timing, and rev‑hang adjustments. Many tuners offer specific maps for lightweight flywheels. Additional upgrades that work well together include a lightweight driveshaft, underdrive pulleys, and a carbon fiber or aluminum prop shaft. These further reduce rotational mass and improve acceleration. For daily driving, pairing the flywheel with a short‑shifter and a high‑performance clutch master cylinder enhances the overall feel.

Frequently Asked Questions

Can I install a lightweight flywheel on a stock clutch?

Yes, but the stock clutch is designed for the heavier factory flywheel. The lighter flywheel will put slightly different stress on the clutch system, and you may notice increased wear. Many enthusiasts replace the clutch at the same time for convenience.

Will a lightweight flywheel void my warranty?

If your FR‑S is still under warranty, this modification may void coverage for drivetrain components. Check with your dealer or consult a legal expert. Most high‑mileage owners proceed without issue.

How much does a lightweight flywheel cost?

Prices range from $250 to $600 depending on the brand (e.g., Fidanza, ACT, Exedy). Additional costs include new bolts, transmission oil, and potentially a clutch kit.

Conclusion

Installing a lightweight flywheel on your Scion FR‑S is a rewarding project that transforms the driving dynamics without requiring extensive engine disassembly. The improvement in throttle response and acceleration is immediately felt every time you press the gas pedal. By following this guide carefully, using the right tools, and understanding the trade‑offs, you can upgrade your car with confidence. For further reading, check out FT86Club forums for owner experiences, or consult the Fidanza flywheel page for product specifications. Remember to torque every bolt to spec and enjoy the heightened connection between you and your FR‑S.