VHM High-Compression Cylinder Head Insert for Yamaha YZ125 & Fantic XX125 – 11.20cc

The VHM AE32327-E 11.20cc cylinder head insert is a higher-compression combustion chamber option developed for Yamaha YZ125 and Fantic XX125 2-stroke motorcycles equipped with the VHM AA33203 cylinder head.

Compared with a larger-volume VHM insert, its reduced 11.20cc combustion chamber volume increases the compression ratio, shifting the engine character toward stronger low- and mid-range torque. The result is improved acceleration, more immediate throttle response, and a stronger torque sensation when driving out of corners.

This setup is particularly suited to riders who prioritize corner-exit performance and usable torque over maximum top-speed potential. As with other higher-compression configurations, the increased low- and mid-range response comes with a trade-off in peak top-end performance.

The insert features a -0.10 mm piston height specification, 1.00 mm squish, a 12° flat-top piston crown profile, and a Ø54 mm bore. It is precision-designed to fit the VHM AA33203 cylinder head and can be changed quickly, allowing the engine setup to be adapted for different fuels, track surfaces, elevations, and riding conditions.

When the VHM cylinder head is used together with a VHM CDI, including CD020422 or CD020426, the dedicated secondary insert chart should be used to determine the correct combustion chamber setup.

The insert also features an engraved part-number reference for easy identification during servicing and engine tuning.

This insert is not compatible with the OEM cylinder head and must be used with the VHM AA33203 cylinder head.

Key Features

• 11.20cc higher-compression combustion chamber increases low- and mid-range torque
• Improves acceleration and delivers stronger engine response when exiting corners
• Quick-change VHM insert design allows fast adjustment of engine characteristics
• Designed for setup selection based on fuel, track conditions, elevation, and ignition configuration
• Precision engineered exclusively for use with the VHM AA33203 cylinder head

Technical Specifications