NISMO DOHC Cylinder Head Conversion Kit for Nissan Vehicles with L-6 Engines

The NISMO DOHC Cylinder Head Conversion Kit is a pinnacle engineering solution designed to transform the legendary Nissan L-6 engine from its original SOHC configuration into a high-performance, 24-valve DOHC powerhouse. Utilizing modern racing technology and aerospace-grade aluminum casting, this comprehensive kit features a compact four-valve combustion chamber and a specialized reinforced silent chain drive system to achieve superior thermal efficiency and durability. Designed for professional engine tuners, the conversion allows for a high degree of customization, capable of reaching 300PS and 7,500rpm when paired with an L28 block, and offers optional components specifically for the Fairlady Z (S30 / S31) to accommodate the necessary 24-degree engine tilt and intake clearance.

• When utilized in a NISMO prototype configuration with an L28 engine block bored to 89mm, this conversion kit is capable of producing approximately 300PS and 300Nm of torque with a 7,500rpm redline.
• Engineered specifically for the L-series, the cylinder head features an ultra-compact combustion chamber with a narrow four-valve angle and high-flow tumble ports to ensure ideal combustion efficiency. By utilizing advanced racing engine analysis tools, NISMO has optimized the design to maximize power delivery and performance across the entire RPM range.
• Designed for durability under high-stress conditions, the kit utilizes a reinforced silent chain system featuring a 6.35mm primary pitch and an 8mm secondary pitch to handle increased loads from aggressive cam profiles and stiff valve springs. Every supporting component, including the head and block tensioners, sprockets, and chain guides, is custom-engineered specifically for this setup to ensure easy maintenance and a straightforward installation process.
• For tuners seeking complete customization, semi-finished camshaft blanks are available as an optional add-on, allowing for the grinding of bespoke lobe profiles to meet specific performance requirements.

Optional Parts

• Engine Mount Bracket Kit: Left and right kit; for S30 / S31 only.
• Oil Pan Kit: Main body, baffle plate, strainer, mounting bolts; for S30 / S31 only.
  • Oil Pan Specifications: Transmission fastening gusset integrated structure, aluminum casting
  • Oil Pan Capacity: 5.1 liters
• Intake Manifold Kit: Main body, balance tube, mounting bolts; compatible with multi-port injection and SOLEX / WEBER carburetors, for vehicles equipped with this DOHC Cylinder Head Conversion Kit.
  • Intake Manifold Port Diameter: 45mm
  • Carburetor Mounting Angle: 2°
• Exhaust Manifold: Main unit only; with 2 A/F sensor bosses and NISMO first generation logo, for S30 / S31 only.
  • Exhaust Manifold Specifications: SUS304 steel 6-to-2 equal length exhaust manifold
  • Exhaust Manifold Primary Diameter: 45mm
  • Exhaust Manifold Secondary Diameter: 50mm

Specifications

• Product: Aluminum cast DOHC 4 valve
• Valve Type: Direct acting valve
• Valve Clearance Adjustment: Inner shim type
• Cam Drive: Double-stage silent chain system
• Combustion Chamber Diameter: 89mm
• Combustion Chamber Volume: 35.10cc (machined combustion chamber)
• Valve Angle:
  • Intake: 15°
  • Exhaust: 12.5°
• Cylinder Head Front Cover: Machined aluminum (no surface treatment)
• Rocker Cover: Machined aluminum, with the first NISMO logo (no surface treatment, no paint)
• Oil Filler Cap: Machined aluminum, original NISMO logo
• Crank Sprocket: Special tooth profile for silent chains
• Camshaft Diameter: 28mm
• Camshaft Profile: 66°
• Camshaft Lift Amount: 9.75mm
• Camshaft Sprockets: Dedicated teeth for silent chains, valve timing adjustable type
• Intake Valve Head Diameter: 36.50mm
• Intake Valve Stem Diameter: 7mm
• Exhaust Valve Head Diameter: 31.20mm
• Exhaust Valve Stem Diameter: 7mm
• Valve Springs: Reinforced valve springs
• Idler Sprocket: Special tooth profile for silent chains
• Primary Camshaft Timing Chain Pitch: 6.35mm
• Secondary Camshaft Timing Chain Pitch: 8mm
• Tension Chain Guide: Steel chain guide with resin pad
• Slack Chain Guide: Aluminum chain guide with resin pad

What’s Included

• DOHC Cylinder Head Conversion Kit:
  • Cylinder Head Area:
    • 1 | Cylinder head assembly
    • 1 | Cylinder head front cover
    • 9 | Hexagon bolts
    • 2 | Dowel pins
    • 1 | Head bolt set
    • 1 | Heater hose connector
    • 1 | Air relief plug assembly
    • 28 | Camshaft bracket bolts
    • 2 | Plugs
    • 9 | Tapered plugs
  • Rocker Cover Area:
    • 1 | Rocker cover
    • 1 | Rocker cover baffle plate
    • 27 | Machine screws
    • 10 | Rocker cover gaskets
    • 21 | Rocker cover bolts
    • 3 | Studs
    • 3 | Nuts
    • 1 | Oil filler cap
    • 2 | Dowel pins
  • Crank Sprocket:
    • 1 | Crank sprocket
  • Camshaft Area:
    • 2 | Camshafts
    • 2 | Cam sprockets
    • 2 | Plugs
    • 12 | Intake valves
    • 12 | Exhaust valves
    • 24 | Valve springs
    • 24 | Outer valve spring seats
    • 24 | Oil valve seals
    • 24 | Valve spring retainers
    • 48 | Valve spring collets
    • 24| Valve spring lifters
    • 2 | Plugs
    • 2 | Washers
    • 10| Cap bolts
    • 2 | Plain washers
  • Chain Area:
    • 1 | Idler sprocket
    • 1 | Idler gear shaft
    • 1 | Idler gear plate
    • 1 | Hexagon bolt
    • 1 | Primary camshaft timing chain
    • 1 | Secondary camshaft timing chain
    • 1 | Chain tensioner assembly
    • 1 | Chain tensioner
    • 1 | Tension chain guide
    • 1 | Slack chain guide
    • 1 | M8 slack guide pivot bolt
    • 2 | Plugs
    • 4 | Hexagon bolts
  • Chain Guide:
    • 1 | Crank sprocket chain guide
    • 3 | Bolts
  • Around the Water Outlet:
    • 1 | Water outlet
    • 3 | Water outlet gaskets
    • 7 | Hexagon bolts
    • 3 | Studs
    • 3 | Plain washers
    • 3 | Hexagon nuts
  • Ignition Coil:
    • 6 | Ignition coil assembly
    • 6 | Ignition coil bolts
  • Intake Manifold Gasket:
    • 1 | Intake manifold gasket
    • 14 | Studs
    • 14 | Hexagon nuts
    • 14 | Spring washers
    • 14 | Plain washers
  • Exhaust Manifold Gasket:
    • 2 | Exhaust manifold gaskets
    • 24 | Studs
    • 24 | Hexagon nuts
• Optional Parts:
  • Oil Pan Kit:
    • 1 | Oil pan
    • 1 | Oil pan baffle plate
    • 6 | Rubber baffle plate flaps
    • 6 | Hexagon bolts
    • 31 | Oil pan bolts
    • 1 | Oil pan drain plug
    • 1 | Oil pan drain plug washer
    • 1 | Oil strainer
    • 1 | Oil strainer gasket
    • 6 | Hexagon bolts
    • 4 | Plain washers
    • 3 | Hexagon nuts
    • 1 | Oil level gauge
  • Engine Mount Bracket Kit:
    • 1 | Right engine mount bracket
    • 1 | Left engine mount bracket
    • 8 | Hexagon bolts
  • Intake Manifold Kit:
    • 1 | Intake manifold
    • 1 | Balance tube
    • 6 | O-ring seals
    • 5 | Bolts
    • 1 | Booster hose connector
    • 1 | Vacuum hose connector
    • 1 | Positive crankcase ventilation valve
    • 1 | Tapered plug
  • Exhaust Manifold:
    • 1 | Exhaust manifold

Confirmed Applications

• Nissan Fairlady 240Z: S30, S31 | 1970-1978 | L24 2.4L I6
• Nissan Fairlady 260Z: S30, S31 | 1974-1978 | L26 2.6L I6
• Nissan Fairlady 280Z: S30, S31 | 1975-1978 | L28E 2.8L I6

Recommended Conditions of Use

• While this kit is engineered to support a maximum output of approximately 300PS, 300Nm of torque, and a 7,500rpm redline, these performance figures are contingent upon the integrity of the engine’s bottom end and cannot be guaranteed. For vehicles driven under high-load conditions, such as circuit racing, a complete teardown and inspection is recommended every 1,000 miles (1,600km). Even for standard street use, it is essential to adhere to the maintenance schedule provided by your engine builder and perform periodic internal inspections to ensure long-term reliability.
• For installation in a Fairlady Z (S30 / S31), the engine mounting orientation must be rotated 24° relative to the factory position to provide necessary clearance for the intake system. While the standard SOHC engine tilts 12° to the right, this DOHC kit requires a 12° tilt to the left. To facilitate this configuration and avoid interference with the suspension crossmember, dedicated engine mount brackets and a specialized aluminum oil pan are available as options. The aluminum oil pan features an integrated gusset for increased transmission mounting rigidity, along with a rubber-flap baffle plate and a specific oil level gauge to prevent oil starvation during high-G cornering. While matching intake and exhaust manifolds are also available, please note that the transmission is not included. A transmission compatible with a 12° left-hand tilt must be custom-manufactured or sourced separately to complete the drivetrain.

Installation Notes

• Installation of this kit requires comprehensive engine building expertise beyond simple head assembly. The process involves modifying the bottom end, sourcing compatible intake and exhaust components, performing a full engine build, and managing the final vehicle integration and tuning to ensure proper operation.
  • Main Parts Required for Engine Assembly:
    • Target Vehicles:
      • Fairlady Z S30 / S31
      • Other
    • DOHC Conversion Kit:
      • Fairlady Z S30 / S31: This product
      • Other: This product
    • Oil Pan:
      • Fairlady Z S30 / S31: This product
      • Other: Customer procurement
    • Engine Mount Bracket:
      • Fairlady Z S30 / S31: This product
      • Other: Customer procurement
    • Intake Manifold:
      • Fairlady Z S30 / S31: This product
      • Other: This product
    • Exhaust Manifold:
      • Fairlady Z S30 / S31: This product
      • Other: Customer procurement
    • L28 Cylinder Block:
      • Fairlady Z S30 / S31: Customer procurement
      • Other: Customer procurement
    • Other Lower Waist Parts:
      • Fairlady Z S30 / S31: Customer procurement
      • Other: Customer procurement
  • Main Parts Required for Vehicle Installation:
    • Target Vehicles:
      • Fairlady Z S30 / S31
      • Other
    • Muffler:
      • Fairlady Z S30 / S31: Customer procurement
      • Other: Customer procurement
    • Transmission:
      • Fairlady Z S30 / S31: Customer procurement
      • Other: Customer procurement
    • Transmission Mount:
      • Fairlady Z S30 / S31: Customer procurement
      • Other: Customer procurement
    • Propeller Shaft:
      • Fairlady Z S30 / S31: Customer procurement
      • Other: Customer procurement
    • Fuel Supply Device:
      • Fairlady Z S30 / S31: Customer procurement
      • Other: Customer procurement
    • Igniter:
      • Fairlady Z S30 / S31: Customer procurement
      • Other: Customer procurement

Product Notes

• This kit is provided as a specialized component set for SOHC to DOHC conversion and is sold without a product warranty. Because it is a technical material kit, all engine assembly, vehicle integration, and operational guarantees are the sole responsibility of the professional installation shop performing the work.
• This conversion kit is engineered specifically for use with an L28 engine block featuring an increased 89mm bore. Please note that NISMO has not verified compatibility or performance with any other engine configurations.
• This high-performance upgrade may result in a notable decrease in ride comfort, daily convenience, and fuel economy, and could impose specific limitations on how the vehicle is driven. Prospective buyers should fully understand the specialized nature of this kit and are strongly encouraged to consult with an expert shop specializing in advanced engine tuning and heritage vehicle restoration prior to purchase.
• Reliability and longevity of these components are highly dependent on the condition of the engine block, the quality of auxiliary parts, and the accuracy of the fuel and ignition tuning. If paired with worn-out hardware or improper timing settings, there is a risk of component failure or catastrophic damage shortly after installation.
• This product has a limited monthly production quantity, so delivery may take some time
• The optional exhaust manifold is not polished, so streaks and other marks from the manufacturing process will remain
• The optional exhaust manifold does not have a heat shield
• While this kit has been engineered, tested, and validated for Japanese-spec models, compatibility with vehicles produced for other markets has not been verified. Performance and fitment on non-Japanese specifications are not guaranteed.
• Given the age and natural wear of vintage vehicles, installation may be challenging or require custom modifications to account for individual chassis variances. Please be aware that the installation process could potentially affect or cause damage to adjacent, aging components.
• Based on the specific requirements of the build, it may be necessary to replace, modify, or adjust auxiliary components to ensure proper integration, guided by official maintenance protocols and the expertise of your professional installation shop.
• The image displays a prototype currently under development. The complete engine shown is for illustrative purposes only and is not available for purchase.
• The fuel supply system is not included in the kit
• The fuel supply system is compatible with both injection type and carburetor type
• Uses genuine Nissan parts and dedicated product parts
• PCV valve is included

Disclaimer

• NISMO provides no warranty for this product beyond initial manufacturing defects. NISMO assumes no liability for damage to the vehicle or other components resulting from the installation of this part, nor will they compensate for labor costs, shipping fees, or incidental expenses incurred during removal and installation. Furthermore, NISMO is not responsible for any direct or indirect losses, engine failures, accidents, or third-party damages arising from the use of this product.

About NISMO

Established as the specialized performance arm of Nissan, Nissan Motorsports & Customizing Co., Ltd. (commonly known as NISMO) serves as the pinnacle of the brand’s racing heritage and engineering excellence. By integrating the high-stakes innovation of global motorsport competition—from Super GT to Formula E—directly into consumer-facing performance parts and vehicles, NISMO bridges the gap between the track and the street. The company is dedicated to providing enthusiasts with elite-level tuning, authentic restoration components for “Heritage” models, and meticulously engineered parts that enhance the driving dynamics, aerodynamics, and soul of the Nissan lineup.