HKS Grommet Type Head Gasket FA24 t=1.2

Grommet Type Head Gasket for FA24, 1.2mm Thickness

The HKS Grommet Type Head Gasket for the FA24 at 1.2mm thickness is the thicker specification of HKS's fire ring head gasket for the 2022+ Toyota GR86 and Subaru BRZ. The additional thickness versus the 0.8mm version reduces the effective compression ratio. Useful for boosted applications where lower compression reduces detonation risk, or where a head resurfacing has reduced deck height and a thicker gasket is needed to compensate.

Specs & Highlights

• Grommet type head gasket construction
• 1.2mm thickness, reduces compression ratio versus 0.8mm
• Fire ring bore sealing design
• FA24 specific fitment
• Appropriate for boosted or resurfaced FA24 applications
• Fitment: 2022+ Toyota GR86 / Subaru BRZ (FA24)

11.5:1 Compression, 0.4-0.6 Point Reduction vs 0.8mm

The t=1.2mm grommet gasket reduces FA24 compression ratio by approximately 0.4–0.6 compression ratio points versus the t=0.8mm, depending on combustion chamber volume. This is appropriate for FA24 builds targeting 1.0–1.5 bar (14–22 psi) boost, where the lower compression ratio provides additional detonation margin on premium fuel. Bore diameter is 91.0mm. The additional 0.4mm thickness versus the 0.8mm version also serves as a deck height compensation when a head resurfacing of 0.3–0.5mm has been performed.

Why Boosted FA24 Builds Use the 1.2mm Thickness

The 1.2mm thickness is the specification for FA24 builds running significant boost levels where the slightly lower compression ratio provides additional detonation margin. It is also the correct choice when a head resurfacing has removed material and the deck height needs compensation to maintain proper quench area and compression ratio.

Head Resurfacing Compensation and Boost Margin

The 0.8mm version maintains factory compression more closely and is appropriate for most naturally aspirated performance builds. Choose the 1.2mm when your specific build requirements. Boost level, head work, piston selection, call for the compression ratio reduction it provides.

The FT Breakdown

The 1.2mm grommet gasket is the forced induction or heavy build specification for the FA24. Same fire ring construction and sealing quality as the 0.8mm; the thickness choice is determined by the engineering requirements of your specific build. The 0.4–0.6 compression ratio point reduction from the t=1.2mm versus t=0.8mm gasket is the difference between an engine that will handle 1.0–1.5 bar on premium fuel reliably and one that may experience detonation events under sustained load. On a forced induction FA24 build where the tune is pushing toward the detonation threshold, that margin is the safety factor that allows the tune to be aggressive without requiring race fuel.