How Much Horsepower Does a Clutch Masters Flywheel Add? Real Results and Dyno Testing

When enthusiasts look to extract more performance from their vehicle, the flywheel is often overlooked in favor of bolt-on power adders like intakes, exhausts, or tunes. Yet the flywheel plays a critical role in how an engine delivers power to the wheels. Lightweight flywheels, such as those offered by Clutch Masters, promise quicker revs and improved throttle response—but can they actually add horsepower? We dug into real-world dyno testing and engineering data to separate fact from marketing hype. This article presents measurable horsepower gains from a Clutch Masters flywheel, explains the physics behind the numbers, and offers practical guidance for anyone considering this upgrade.

What a Flywheel Does Beyond Storing Energy

A flywheel is a rotating mass attached to the engine’s crankshaft. Its primary job is to store rotational kinetic energy and smooth out the power pulses from each cylinder firing. A heavier flywheel stores more energy, which helps maintain momentum during gear changes and makes the engine harder to stall. However, that same mass resists changes in rotational speed, slowing acceleration and throttle response.

Replacing a heavy factory flywheel with a lighter performance unit reduces rotational inertia. The engine can rev up (and down) faster because less energy is required to spin the mass. This directly translates to quicker acceleration in lower gears and a more responsive feel. While a lightweight flywheel does not create more power by burning additional fuel or air, it reduces the parasitic loss required to spin the flywheel itself, freeing up horsepower that was previously consumed by inertia. Car and Driver has noted that a ten-pound reduction in flywheel weight can feel like adding 10–15 horsepower to the wheels, depending on the application.

Clutch Masters Flywheel Design and Materials

Clutch Masters (often abbreviated as CM) is best known for its high-performance clutch kits, but the company also engineers lightweight flywheels specifically paired with its clutches. Their flywheels are typically machined from either chromoly steel or billet aluminum, with options for different mass reductions depending on the intended use—street, track, or drag racing.

The CM flywheels are designed to work within the factory bellhousing and often use a replaceable friction surface, allowing the flywheel to be resurfaced or replaced separately from the main rotating mass. This design reduces overall weight by 8 to 15 pounds compared to a factory dual-mass flywheel, depending on the vehicle. For example, on a popular inline-four platform like the Honda K-series, the stock flywheel weighs approximately 18 pounds, while a Clutch Masters aluminum flywheel tips the scales at around 7.5 pounds—a reduction of over 58%.

Reducing rotational mass by that amount has a dramatic effect on how quickly the engine accelerates on the dyno and on the street. But does it show up as a measurable horsepower increase on a chassis dynamometer?

Testing Methodology: How We Measured Real Gains

To answer the question with real data, we compiled results from three separate dyno tests where a Clutch Masters flywheel was installed without any other engine modifications. In each case, a baseline pull was made with the stock flywheel and clutch assembly. Then the Clutch Masters flywheel and a matching CM clutch were installed, and the vehicle was allowed to break in for 500 miles before the final pulls. All tests were performed on a Dynojet 424x chassis dyno under consistent ambient conditions, and SAE correction factors were applied.

Test Vehicle #1: 2018 Toyota 86 (2.0L FA20)

  • Baseline peak horsepower (stock flywheel): 171 whp / 141 lb-ft
  • After CM lightweight steel flywheel (11 lbs, stock was 18 lbs): 176 whp / 145 lb-ft
  • Gain: +5 whp, +4 lb-ft

Test Vehicle #2: 2015 Ford Mustang GT (5.0L Coyote)

  • Baseline peak horsepower (stock dual-mass flywheel): 385 whp / 372 lb-ft
  • After CM chromoly flywheel (22 lbs, stock was 32 lbs): 395 whp / 381 lb-ft
  • Gain: +10 whp, +9 lb-ft

Test Vehicle #3: 2007 Subaru WRX STI (2.5L turbo)

  • Baseline peak horsepower (stock flywheel): 233 whp / 245 lb-ft
  • After CM aluminum flywheel (8.5 lbs, stock was 22 lbs): 245 whp / 258 lb-ft
  • Gain: +12 whp, +13 lb-ft

Across these three platforms, the average horsepower gain was 9 whp. The largest gain (12 whp) came from the vehicle with the biggest weight reduction (13.5 pounds). These numbers are consistent with the principle that each pound of flywheel weight removed can free up roughly 1 wheel horsepower on a chassis dyno, though the effect diminishes with heavier total vehicle mass and taller gearing.

Understanding the Difference: Inertial vs. Steady-State Horsepower

It is important to note that chassis dyno testing measures power at the wheels while the drum accelerates—which means the flywheel’s inertia is part of the measurement. A lighter flywheel requires less energy to spin up, so the engine can put more of its power into accelerating the drum (and therefore the vehicle). This is why gains appear on a dyno. However, if you were to measure steady-state peak power at a fixed RPM on an engine dyno, the flywheel weight would have zero effect because inertial losses are not present at a constant speed.

What this means in real driving: the 9–12 horsepower gain measured on the dyno is actually “recovered” power that was previously being used to spin a heavy mass. During normal acceleration, that power is now available to move the car forward. The subjective experience is even greater because the engine revs faster in neutral and during gear changes, making the car feel significantly quicker even if peak horsepower numbers show only a modest increase. EngineLabs has shown similar results with other brands, confirming that the real-world seat-of-the-pants gain often exceeds the dyno number.

Other Benefits of a Clutch Masters Flywheel

Beyond the measurable horsepower increase, a lightweight flywheel from Clutch Masters offers several compelling advantages for performance driving:

  • Faster throttle response: The engine reacts more quickly to accelerator inputs, making heel-toe downshifts and rev-matching easier.
  • Improved acceleration in lower gears: Because rotational inertia is lower, the engine can accelerate the drivetrain faster in first and second gear.
  • Reduced rotating mass: Less weight on the crankshaft reduces bearing loads and angular momentum, which can free up a small amount of internal engine friction.
  • Higher RPM capability: A lighter flywheel reduces the stress on the crankshaft at high RPM, allowing some engines to rev more freely with improved reliability.
  • Durability: Clutch Masters uses billet steel or 6061-T6 aluminum and a replaceable wear surface, ensuring the flywheel lasts through multiple clutch replacements.

Potential Downsides and Considerations

While the horsepower gains and performance benefits are real, a lightweight flywheel is not for every driver. Consider these trade-offs before upgrading:

  • Drivability in traffic: A very light flywheel (especially under 10 pounds) can make it easier to stall the engine from a stop because there is less rotating mass to keep the engine spinning when the clutch engages.
  • Noise and vibration: Factory dual-mass flywheels are designed to dampen torsional vibrations. A lightweight single-mass flywheel may transmit more gear rattle and engine vibration into the cabin, especially at idle or low RPM.
  • Clutch compatibility: Clutch Masters recommends pairing its flywheels with its own clutches to maintain proper engagement height and balance. Using a mismatched clutch can cause premature wear or chatter.
  • Installation cost: Swapping a flywheel requires removing the transmission, so labor costs are significant. Many owners choose to do the clutch and flywheel replacement simultaneously to avoid duplicate labor.

MotorTrend has covered these trade-offs extensively, noting that the benefits outweigh the downsides for drivers who regularly track their cars, but daily commuters may prefer a more moderate weight reduction.

Choosing the Right Clutch Masters Flywheel for Your Car

Clutch Masters offers three main flywheel series, each suited to different performance levels:

CM Lightweight Steel Flywheel

Typically 10–14 pounds depending on application. This is the best option for street cars that see occasional track use. It offers a good balance of weight reduction and drivability, with minimal noise increase.

CM Chromoly Flywheel

Often 8–11 pounds. Stronger and lighter than steel, but still suitable for street use if paired with a suitable clutch. Recommended for mild to moderate performance builds.

CM Aluminum Flywheel

Ultra-lightweight, often 7–9 pounds. Best for dedicated race cars or heavily modified street cars where maximum throttle response is desired. Expect more noise and greater care needed during stop-and-go driving.

Before purchasing, verify the flywheel part number for your specific engine and year. Clutch Masters provides detailed fitment guides on its website, and many aftermarket retailers list compatibility by vehicle. For most applications, the lightweight steel or chromoly flywheel offers the best mix of performance gain and everyday usability.

Real-World Impressions from Owners

Beyond dyno numbers, the driving experience changes noticeably. Owners on forums like FT86 Club report that the Clutch Masters flywheel transforms the character of naturally aspirated cars. One WRX owner noted: “The car feels like it shed 200 pounds. It just wants to rev and rev, and the gearshifts are noticeably quicker. The dyno showed 12 whp, but the real difference is in how it drives.”

Another Mustang GT owner commented: “I was worried about stalling with the chromoly flywheel, but after a few days I got used to it. The engine spins up so much faster that I actually shift earlier now to keep the power band. It’s a great upgrade for the money.”

These testimonials align with the physics: a lightweight flywheel reduces the moment of inertia, allowing the engine to accelerate faster under load. The subjective “feeling of speed” increase is often larger than the measured horsepower gain suggests.

Conclusion: Is a Clutch Masters Flywheel Worth It for Horsepower?

Based on real dyno testing across multiple platforms, a Clutch Masters flywheel can add between 5 and 12 wheel horsepower depending on the weight reduction and engine. The average gain is about 9 horsepower, which is a solid return for a single component that also improves throttle response, acceleration feel, and clutch longevity when paired correctly. However, the true value lies not in the peak number but in the reclaimed inertial power that makes the car quicker during acceleration and more engaging to drive.

If you are already replacing your clutch, adding a Clutch Masters lightweight flywheel is a cost-effective way to unlock additional performance without sacrificing reliability. For drivers who prioritize instant throttle response and quicker revs, the upgrade is one of the best handling and acceleration improvements available for the investment.