Cylinder Kit Metrakit 77cc Pro Race 4 Minarelli AM6

Cylinder Kit Metrakit 77cc Pro Race 4 Minarelli AM6

The Metrakit Pro Race 4 represents the next step in one of the most iconic moped tuning cylinders. While it is often compared to the long-running Pro Race 3, the PR4 brings several important updates that go far beyond the displacement increase.

The most obvious change is the larger bore size, giving the cylinder an effective 77cc capacity. But that’s just the beginning: the port timing has been completely reworked, and the port map design has been optimized for improved gas flow. In addition, the combustion chamber has been reshaped from a trapezoidal dome to a spherical geometry, which – together with the rounded piston crown – distributes combustion forces more evenly, enhancing both power delivery and durability.

The piston itself, manufactured by Athena, remains graphite-coated to reduce wear during break-in. Thanks to the new timing setup, the piston design has also been fine-tuned for perfect fitment. Each piston is individually matched to the cylinder after boring, coating, and honing, ensuring maximum precision.

Technical Specifications

• Cylinder & head material: Aluminium alloy

• Coating: NiCaSil

• Bore: 50 mm

• Stroke: 39 mm