The Case for Crazy Performance
Brand-new 6160 aluminium 25/30HP engine crank case.
Made in Australia.
Engineered for serious vintage speed.
Zero Mile Casting.
Backwards Compatible Core Components.
Contact WTF@AirCooledAsylum.com.
The WHY
Reimagining the Original Air Cooled 25hp/30hp Crankcase
Honouring an Icon While Unlocking Its Potential
Few engines have earned the legendary status and reputation for simplicity, reliability and longevity of the original 25hp and 30hp powerplants.
Having spent more than 40 years involved in the vintage air-cooled scene and working extensively with this family of engines, Air Cooled Asylum has developed a deep appreciation for the brilliance of the original design. At the same time, decades of hands-on experience have highlighted several areas where a modern engineering approach can enhance the platform without compromising its character.
This new crankcase has been developed to preserve the spirit of the original engine while overcoming many of the limitations inherent in a design conceived during the 1930s.
Why the Original Air-Cooled 25hp/30hp Cases Needed Improving
The original crankcase performs exceptionally well in standard and mildly modified applications. However, for enthusiasts seeking increased displacement, greater reliability under load, or more ambitious performance builds, certain limitations become apparent.
- Enhanced case structure with revised material dimensioning and support.
- Cast in aluminium for higher potential output and increased displacement.
- Shuffle-pinned main stud areas for improved crankshaft stability under load.
- Increased crankshaft-to-camshaft centre distance (+100 thou / 2.5mm).
- Integral oil gallery threads for external oil systems and oil returns.
- External oil relief arrangement for more consistent oil pressure.
- Compatibility with later 1600cc-style oil pumps, dipsticks and dowel pins.
- Compatibility with later 1600cc-style cam followers.
- Main bearing #1 stud locations moved slightly wider.
- Provision for original or alternative cylinder head stud configurations.
- Capability to use either original Wolfsburg or Stuttgart camshaft configurations.
- Additional provision for discreet bespoke sensors, linkages and brackets.
Backwards Compatibility — Respecting the Original Design
One of the primary objectives of this project was to ensure that enthusiasts could retain as much of their original engine hardware as possible and still look correct in the engine bay of early air-cooled vehicles.
Core components including the crankshaft, flywheel, connecting rods, camshaft, oil sump plate, engine tinware, and potentially the pistons, cylinders and cylinder heads can all be transferred to the new crankcase.
Performance Potential and Future Possibilities
The increased 2.5mm separation between the crankshaft and camshaft, combined with additional material around cylinders #2 and #3, creates opportunities that simply did not exist with the original casting.
For builders pursuing larger displacement engines, increased power output, or unique custom combinations, this crankcase provides a significantly stronger foundation while maintaining compatibility with the classic architecture enthusiasts know and love.
The Story Behind the Design
The origins of this project stretch back more than four decades. As young enthusiasts, the founders were given a 1958 air-cooled engine to dismantle and learn from. Even then, it was clear that the original engineers had created something remarkable.
This crankcase is the answer to a long-held question: how can the original concept be evolved using modern materials and engineering practices while remaining faithful to the dimensions, components and heritage that enthusiasts value?
It is not intended to replace the original design, but rather to represent its logical evolution — a bridge between the pioneering early air-cooled engine architecture and the demands of today’s builders. So now you can still appreciate the past, but aren’t limited by it.