Bourne HPP Lightened Chromoly Steel Flywheel for K Series

Bourne HPP Lightened Chromoly Flywheel - K20/K24 (RSX Type S, TSX, Civic Si & Type R)

The flywheel is a heavy disc bolted to the back of your crankshaft, and it does two jobs: it stores rotational energy to smooth the engine out, and it carries your clutch. The factory flywheel is deliberately heavy, which makes for an easy, smooth idle and a forgiving launch, but all that stored inertia is also dead weight the engine has to spin up and slow down every time you touch the throttle. This Bourne HPP flywheel strips that weight away. It's a one-piece 4140 forged chromoly unit that comes in at just 3.5kg (about 7 pounds), and the difference in how the engine responds is something you feel immediately.

What a Lighter Flywheel Does

Less rotating mass means the engine is no longer dragging a heavy wheel up and down the rev range. It revs up faster and more eagerly off throttle, and just as importantly it revs down faster, which makes rev-matching on downshifts crisp and easy and makes heel-toe feel natural. On a K-series that loves to rev, the car feels noticeably more alive and connected. This is exactly what you want on a track or road race car, where throttle response and quick, clean downshifts matter on every corner.

Be honest with yourself about the trade-off, because every lightweight flywheel has one. With less stored inertia, the idle can feel a touch busier and pulling away from a dead stop takes slightly more clutch and throttle finesse than the heavy factory wheel, especially on a hill. For a track-focused or spirited car that's a non-issue and a fair trade for the response you gain. If your car is a pure daily that mostly crawls in traffic, just know it changes the low-speed feel a little.

One-Piece Chromoly, No Pressed-On Ring Gear

This is where the chromoly construction earns its place. The whole flywheel, including the ring gear teeth your starter engages, is machined from a single piece of 4140 forged chromoly steel, which Bourne rates at roughly double the strength of standard billet steel. That one-piece design matters for a real safety reason: many lightweight aluminum flywheels use a separate ring gear pressed onto the body, and under hard use that ring gear can work loose or separate. Milling the teeth directly into the forging eliminates that failure point entirely. The flywheel has been tested to 12,000 RPM and exceeds SFI 1.1 specifications, so it's certified safe for high-revving and competition use, and the steel friction surface can be resurfaced down the road rather than discarded like a worn aluminum face.

Built to Civic Cup Spec

The 3.5kg weight isn't arbitrary. This flywheel was engineered to meet the minimum weight requirement of Civic Cup regulations, so it's built to be as light as the rules allow while staying legal for that series. If you're running Civic Cup or a similar spec class, it's purpose-made for you. If you're not, you simply benefit from a flywheel that's been developed to a real competition standard. It's CAD-designed, CNC-machined, and computer-balanced, and the design also routes airflow around the clutch assembly to help shed heat during hard track sessions.

Clutch Compatibility

This flywheel is built to work with the clutch you want to run, and it's compatible with a wide range of K-series clutch kits, including Exedy, ACT, Fidanza, Clutchmasters, and OEM Honda clutches. Match it to the clutch that suits your power and use, and confirm your specific clutch is spec'd for a chromoly steel flywheel before ordering.

Install Note

When you install it, use fresh flywheel bolts and torque them to spec in the correct sequence. K-series flywheel bolts are a critical fastener spinning at engine speed, so this isn't the place to reuse old hardware or guess at the torque.

Fitment

Fits the K-series engines and transmissions in these cars:

• 2002-2006 Acura RSX Type S (K20A2, K20Z1)
• 2004-2008 Acura TSX (K24A2)
• 2006-2011 Honda Civic Si (K20Z3)
• DC5 Integra Type R (K20A)
• EP3 Honda Civic Type R (K20A)

Fits the K20A, K20A2, K20Z1, K20Z3, and K24A2 engine and transmission combinations.