Reviving a Classic – The Introduction of the Mini Sport 1275cc Cylinder Head

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New 1275cc Cylinder Head - performance

The classic Mini is an icon, and at its heart lies the legendary A-Series engine, a marvel of British engineering that powered Minis through decades of motorsport success and road-going adventures. However, with time, even the most robust components of the A-Series have become harder to source, especially the 12G940 cylinder head, a cornerstone of Mini performance.

New casting, 12G940 1275cc Cylinder head for classic Mini.

Standard - 12G940 1275cc Cylinder Head for Classic Mini 

Recognising the growing demand for a reliable, high-performance solution, Mini Sport has collaborated with esteemed designer and manufacturer Will McGregor to reimagine the 1275cc cylinder head for today’s enthusiasts. The result is a precision-engineered masterpiece that revives the past while incorporating modern advancements, ensuring the A-Series engine remains as relevant and powerful as ever.

Inspiration: Breathing New Life into a Classic

The idea to produce a brand-new 12G940 cylinder head was born out of necessity and passion. As Will McGregor explains, “The scarcity of good used castings has made it incredibly challenging for Mini enthusiasts to find cylinder heads they can trust. Hours of work often go into refurbishing an old head, only to discover cracks or weaknesses that render it unusable.”

close up of cylinder head classic mini

Performance - 12G940 Stage 3  1275cc Cylinder Head for Classic Mini

Beyond availability, there was also the need for a solution that accommodated larger valves—a common modification for improving Mini engine performance. Existing heads simply weren’t designed to handle such upgrades, leading to compromises that limited their potential.

Overcoming Challenges: A Journey of Innovation

Designing and manufacturing a new cylinder head in cast iron isn’t a task for the faint-hearted. “The first problem we faced,” Will recalls, “was the movement of internal water jackets during casting. Due to the weight of cast iron, the sand cores would shift, leading to inconsistencies.”

cylinder head classic mini green

Destructive testing pushed the casting to its limits. “We wanted to know exactly where the weaknesses lay,” says Will. “By removing those weaknesses, we’ve given enthusiasts the confidence to modify their cylinder heads beyond previous limitations.”

Modern Modifications for a Timeless Design

Through extensive discussions with engine builders and meticulous research, a list of improvements was created to address the limitations of the original casting. These included:

  • Raising intake ports to maximise airflow.
  • Enlarging combustion chambers for increased efficiency.
  • Fitting the largest possible valves for improved power.
  • Reinforcing spring platforms and other high-stress areas to prevent failure.
Close up of the Standard Mini 1275cc head

Putting It to the Test

No innovation is complete without rigorous testing, and the new cylinder head was subjected to an exhaustive evaluation process. A prototype was built to standard road specifications and installed on a test engine. The engine was heat cycled repeatedly, with meticulous checks for leaks, warping, and pressure integrity.

From the rolling road to the Dyno, the head endured multiple pulls under varying conditions. After testing, the head was disassembled and inspected, with every component scrutinised for signs of stress. Larger valves, hardened exhaust seats, and further modifications were added and retested to ensure the head could handle even extreme configurations.

Cylinder head red for classic mini

The Result: A Cylinder Head Built for the Future

The Mini Sport 1275cc cylinder head is more than a replacement for the original—it’s an evolution. Manufactured entirely in Yorkshire using BS1452 Grade 250 cast iron, this head combines classic British craftsmanship with modern engineering. Available in both Standard and Performance variants, it caters to the needs of enthusiasts who value reliability, power, and precision.

As a final step, multiple engine builders were given cylinder heads to test and provide feedback. Their insights shaped the final specifications, ensuring the product meets the needs of the Mini community.

cylinder head springs

Conclusion: A New Chapter for the A-Series Engine

With the launch of the Mini Sport 1275cc cylinder head, the legacy of the A-Series engine continues to thrive. Whether you're restoring a classic Mini or seeking to unlock its full performance potential, this cylinder head represents the perfect blend of heritage and innovation.

Stay tuned  & follow us on Instagram, Facebook & Youtube for more insights into the design process, the challenges overcome, and the performance benefits of this exciting new product. Mini Sport is proud to bring this exceptional product to market, ensuring the classic Mini remains an enduring symbol of British motoring excellence.