VHM Cylinder headset with insert for GasGas MC 85 21-24

VHM cylinder heads with exchangeable combustion chamber. VHM produces exchangeable cylinder heads for two-stroke engines in motocross and road racing. With the experience gained in two-stroke tuning, VHM develops products of high quality.

The combustion chamber is very easy to change, just untighten the cylinder head, take it off and you can change the combustion chamber. This makes it very easy to adjust the combustion ratio to different tracks and fuels that are used. Combustion chambers are available in different volumes.

During intensive tests, on the racetrack as on the VHM testbench, the cylinder head showed a better temperature development in the cylinder head. A lower engine temperature followed. The explanation of this phenomenon is the use of a special aluminum alloy which has a very good heat transference. Another advantage of the material is its resistance to detonation. It's also possible to design your own combustion chamber, just take a blind combustion chamber and you can make any type that you want.

• Cylinder/s head/s.
• Insert/s Combustion chamber.
• All the necessary O-seals. 

• No head gasket required uses double o-rings which also keep the squish more accurate. No need for messy sealants.
•  Give significant power boost over standard heads, no re-jet required. Improved cooling and combustion chamber shape, straight plug positioning. (Front fairing hole may need slight opening up to allow plug fitment)
• Extremely high grade CNC billet aluminium.
• Weight saving for the material used.
• Flame area spread over the whole piston surface resulting in both a better burn and higher piston durability.
• The cylinder heads are Hard Anodised 
• Water jacket is approx 25% larger than standard which in turn means the cylinder heads run considerably cooler than stock. This means that there is a lot wider scope for further engine tuning without cooling issues arising. Bleed screw added making bleeding the water system that little bit easier.
• Supplied with O-ring set.
• They are avaible in some different configuration. 

 STANDARD OPTION: where is indicated in the table. VHM, after intensive testing on the dyno and on the track,  developed inserts with the best combustion profile. This “standard” inserts gives the best performance with a standard piston and piston height (deck height) is irrilevant if you have a race exhaust or reed case etc.

If you select the Special insert according to your specification you must specify: Volume, Piston Height, Squish and Combustion chamber profile. (We will send a file PDF that you must compile for make your request).

WHAT DOES IT MEAN THE MEASURE IN THE UPPER TABLE?

BE SURE THAT THE PISTON IS AT THE Top Dead Center (TDC):

Volume: Volume combustion chamber including volume spark plug hole, when piston is at TDC.

Piston Height: Differents between top of piston and cilinderdeck when piston is at TDC.

Squish thickness:  Minimum distance between piston and insert when the piston is at TDC.

The compression ratio: can be adjusted quickly, by increasing or decreasing the volume of the combustuon chamber, depending on the track and weather conditions. 

- With a higher compression ratio, which means less volume, will give the the engine more low and midddle range torque. This will improve the acceleration and inreased torque feeling, when turning out of the corner.

- Lowering the compression ratio, which means more volume, will result in better overrevolution characteristics. We advise MX drivers to use inserts with a bigger volume on fast tracks to improve topspeed. 

Partnumber sealkit: SK33145