HKS 23001-AM005 Stopper Type MLS Head Gasket 4G63T 1.6mm 86mm Lancer EVO IV-IX

Vehicle Fitment

• 1996 Mitsubishi Lancer Evolution IV (CN9A), 4G63T Turbocharged Inline-4, AWD
• 1997-1998 Mitsubishi Lancer Evolution V (CP9A), 4G63T Turbocharged Inline-4, AWD
• 1999-2001 Mitsubishi Lancer Evolution VI / VI Tommi Makinen Edition (CP9A), 4G63T Turbocharged Inline-4, AWD
• 2001-2003 Mitsubishi Lancer Evolution VII (CT9A), 4G63T Turbocharged Inline-4, AWD
• 2003-2005 Mitsubishi Lancer Evolution VIII / VIII MR (CT9A), 4G63T Turbocharged Inline-4, AWD
• 2005-2006 Mitsubishi Lancer Evolution IX / IX MR (CT9A), 4G63T Turbocharged Inline-4, AWD

Fitment Notes

• Bore size is 86mm - matches the OEM cylinder bore of the 4G63T across all EVO IV-IX variants; also accommodates engines that have been bored to standard oversizes
• The 1.6mm thickness is the thickest option in HKS's 4G63 stopper gasket range - at 1.6mm the compressed gasket height is greater than both the 1.0mm (23001-AM003) and 1.2mm (23001-AM004) options, resulting in a lower dynamic compression ratio; this thickness is appropriate for high-boost applications where reducing compression ratio provides additional detonation safety margin, and for engines with machined or thinner-than-stock head surfaces
• Compression ratio reference values (stock head, stock pistons): 8.2 for standard EVO IV-VIII applications; 8.5 for CT9A MR variants - actual compression ratio in your build will vary based on piston selection, head surfacing, and combustion chamber volume
• Head surface must be clean, flat, and within factory tolerance before installation - HKS recommends verifying head flatness and resurfacing if needed prior to gasket installation
• Use with OEM or equivalent grade ARP head studs/bolts and follow correct torque specification - MLS gaskets require proper clamping load to activate the stopper sealing system
• Not CARB legal - not for sale or street use in California or other CARB-compliant states

Features

• Opposed Bead Stopper construction creates a raised step directly around each combustion chamber bore - when the head is clamped down, this stopper concentrates sealing pressure precisely at the highest-risk area (the combustion chamber edge) where cylinder pressure and heat are most intense, creating a more reliable seal than flat multi-layer gaskets under high-boost conditions
• Stopper integrated into the plate structure allows a smaller fold geometry while maintaining full structural integrity - this design places effective stopper sealing in even the tightest areas around the combustion chamber where conventional stopper designs cannot reach
• Independent water holes maintain coolant flow between the cylinder head and block independently from the combustion chamber sealing zones - the water passage apertures are isolated from the combustion area to prevent hot spot sealing failure in the coolant passages
• Multi-layer steel (MLS) construction distributes clamping load across multiple bonded steel layers - each layer works in concert to accommodate minor surface imperfections in the head and block mating surfaces while maintaining overall gasket rigidity and sealing pressure
• Special heat-resistant and corrosion-resistant alloy steel used throughout - engineered to maintain sealing integrity under the sustained high temperatures generated by high-horsepower, high-boost 4G63T builds
• Fluorine rubber coating on sealing surfaces provides an additional conformable layer between the steel gasket and the metal mating surfaces - filling microscopic surface irregularities and preventing fretting and micro-leakage that can develop on bare-steel MLS gaskets over time
• 1.6mm thickness reduces dynamic compression ratio compared to thinner gasket options - directly improving detonation resistance in high-boost and high-output applications where maintaining a safer compression ratio is critical to engine longevity

Specifications

• Part Number: 23001-AM005
• HKS Product Name: HEAD GASKET 4G63(EVO4-9) t=1.6 SMG/K
• Compatible Engine: Mitsubishi 4G63T Turbocharged Inline-4
• Gasket Type: Opposed Bead Stopper Type (SMG/K) with Independent Water Holes
• Construction: Multi-layer steel (MLS), fluorine rubber coated
• Thickness: 1.6mm
• Bore: 86mm
• Compression Ratio (reference, stock head and pistons): 8.2 (standard EVO IV-VIII) / 8.5 (CT9A MR variants)
• Water Holes: Independent
• CARB Legal: No
• Quantity: 1 head gasket

Included Components

• 1x HKS Stopper Type MLS head gasket, 4G63T, 1.6mm x 86mm

Product Description

The HKS 23001-AM005 is the 1.6mm Opposed Bead Stopper Type head gasket for the Mitsubishi 4G63T, covering Lancer Evolution IV through IX across the CN9A, CP9A, and CT9A chassis from 1996 to 2006. It is the thickest option in HKS's three-tier 4G63 stopper gasket range - at 1.6mm it sits above the 1.0mm (23001-AM003) and 1.2mm (23001-AM004) alternatives - and is selected when the build objective calls for a lower dynamic compression ratio: typically high-boost applications, engines with surfaced heads, or builds specifically targeting detonation margin at the expense of static compression. Compression ratio reference values are 8.2 with stock head and pistons on standard EVO IV-VIII applications, and 8.5 on CT9A MR variants.

The Opposed Bead Stopper design is central to what makes HKS stopper gaskets suited for high-output forced induction engines. A raised step is formed directly around each combustion chamber bore - when the head bolts are torqued, this stopper concentrates clamping force precisely at the cylinder edge where combustion pressure peaks and where head gasket failures most commonly originate. The stopper is integrated into the plate structure itself rather than added as a separate ring, which allows it to be placed in close proximity to the combustion chamber wall even where space is constrained. Independent water holes isolate coolant passage sealing from the combustion chamber sealing zones, preventing the thermal cycling that occurs in the combustion area from compromising the water passage seal over time.

The gasket is constructed from multi-layer steel bonded with a special heat-resistant and corrosion-resistant alloy, and finished with a fluorine rubber coating on sealing surfaces that fills microscopic surface irregularities and prevents the micro-fretting that can develop on bare-steel MLS gaskets in high-vibration, high-heat environments. Head flatness should be verified before installation, and proper head stud or bolt torque procedure must be followed to activate the stopper sealing system correctly. This product is not CARB legal and is not available for sale in California.