VHM Low-Compression Cylinder Head Insert for Yamaha YZ250 – 21.00cc
Optional 21.00cc VHM cylinder head insert engineered to reduce compression and improve over-rev, top-end performance, and maximum speed on Yamaha YZ250 2-stroke engines. Ideal for hard-packed tracks, faster layouts, and enduro-style riding.
$94.99
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Product Description
The VHM AE32021-009 21.00cc cylinder head insert is an optional lower-compression combustion chamber developed for Yamaha YZ250 2-stroke motorcycles equipped with the VHM AA33080 cylinder head.
Compared with the standard VHM AE32021-B insert, the larger 21.00cc chamber volume lowers the compression ratio and allows the engine to rev more freely at higher rpm. This shifts the power delivery toward improved over-rev and top-end performance, making the setup especially suitable for hard-packed tracks, fast motocross layouts, and enduro conditions where maintaining speed at higher rpm is more important than maximum bottom-end response.
The trade-off of this lower-compression configuration is reduced low-rpm torque reaction compared with a smaller-volume insert. Riders looking for a smoother, more free-revving engine character and increased top-speed potential can benefit from this setup.
The insert features a 21.00cc combustion chamber volume, +2.80 mm piston height, and 1.50 mm squish specification.
VHM’s interchangeable combustion chamber system allows the insert to be changed quickly without replacing the complete cylinder head, giving riders and engine tuners greater flexibility when adapting the bike to different track conditions, terrain, and performance requirements.
The AE32021-009 is precision-designed for the VHM AA33080 cylinder head and offers good resistance to detonation. An engraved part-number reference allows quick identification during servicing and engine setup.
This insert is not compatible with the OEM Yamaha cylinder head and must be used with the VHM AA33080 head.
Key Features
- 21.00cc larger-volume combustion chamber lowers compression for improved high-rpm performance
- Enhances over-rev characteristics and supports increased top-end speed
- Ideal for hard-packed tracks, fast motocross layouts, and enduro-style riding
- Provides good resistance to detonation under demanding high-rpm operation
- Quick-change VHM insert design allows easy adjustment of engine power characteristics
Technical Specifications
| Specification | Details |
|---|---|
| Manufacturer | VHM |
| Part Number / SKU | AE32021-009 |
| Product Type | Cylinder Head Insert / Combustion Chamber Insert |
| Insert Type | Optional / Lower-Compression |
| Engine Type | 2-Stroke |
| Engine Class | 250cc |
| Combustion Chamber Volume | 21.00 cc |
| Piston Height | +2.80 mm |
| Squish | 1.50 mm |
| Power Characteristic | Increased Over-Rev and Top-End Performance |
| Recommended Use | Hard-Pack / Fast Tracks / Enduro |
| Required Cylinder Head | VHM AA33080 |
| OEM Cylinder Head Compatible | No |
| Identification | Part-number reference engraved on insert |
| Make | Model | Year |
|---|---|---|
| YAMAHA | YZ 250 | 1999 - 2027 |
| YAMAHA | YZ 250 X | 2016 - 2027 |