Classic Mini Unleaded Cylinder head with LARGE Competition Valves SMALL BORE 23.5cc – Fast Road / Track Spec 
 
Small-Bore Road Sport / Track Performance Cylinder Head
 
This is the only modified cylinder head specification offered for small-bore engines, as it represents the most effective and worthwhile upgrade for real-world performance.
 
Developed from carefully selected used core castings, this cylinder head is reworked to a modern Road Sport specification, delivering strong BHP and torque gains while maintaining excellent drivability. It is equally suited to fast road use, track days, hill climbs, and auto-testing when paired with road-sport or super-sport camshafts.
 
Key Specifications
Combustion chamber volume: ~23.5cc (optimised for dished pistons)
Valve sizes:
30.93mm inlet
26.5mm exhaust
Valves: Plasma-nitrided EN214N stainless steel
Valve guides: Latest-spec manganese bronze
Valve springs: Double springs rated at ~180lb (at max lift)
 
Maximum capability:
Up to 7,500 RPM continuous
Up to 0.475" valve lift
Configuration: 9-stud fitting as standard
 
Engineering & Performance Features
Port shapes and dimensions optimised using airflow bench and rolling road development
Valve throat geometry tailored to suit road-sport and super-sport cam profiles
Compression ratios optimised for modern unleaded fuel
Fitted with high-quality Serdi lead-free exhaust seat inserts
Designed for high-performance durability under sustained use
 
Fitment & Compatibility
Heater take-off port open
Bypass hose adapter fitted
Both can be blanked off as required
 
Applications
 
Ideal for:
Fast road builds
Track day / weekend performance cars
Hill climbs and auto-testing
 
 
Stage Classification (Traditional Tuning Reference)
Following original Special Tuning philosophy:
 
998cc Heads
Stage 1: Gas-flowed with standard road valves
Stage 2: Larger 30.9mm inlet (typically race valves)
Stage 3: 30.9mm inlet + 26.4mm exhaust, race-quality valves
 
1275cc Heads
Stage 1: 33mm inlet / 29mm exhaust, gas-flowed
Stage 2: 35.6mm / 29mm, road-quality valves (Road Sport spec)
Stage 3: 35.7mm / 29mm, race-quality valves (Super Sport / GT spec)
Stage 4: As Stage 3, with larger valves and further port/throat development
 
Core must be:
Crack-free
Unmodified (standard casting)
Complete with valves, springs, caps & collets
Non-exchange item
No surcharge applies
 
At Mini World Australia, we focus on parts that actually deliver results—not just claims. This cylinder head is built for drivers who want real, usable performance on the road or track.

Serious airflow = serious power.
 
Please note: This part is bulky and may attract additional freight charges