Dome part number system
Each dome part number has a cc volume reference.
The lower the cc the higher the compression ratio
The first letter and number describe the dome series.  example Y12 is a Y1 series dome.
The second or last number is the dome volume or cc
Part numbers ending with a 1 are closest to stock and can run low octane fuel
Part numbers ending with a 2 are approximately 12:1 and must run 95+ octane fuel
Part numbers ending with a 3 are approximately 13:1 and must run 100+ octane fuel
Part numbers ending with a 4 and 5 approximately 14/15:1 and must run 105+ octane fuel

Performance expectations by dome size
The higher compression dome the more low end power you can expect however top end loss may occur with higher compression domes

Big Bore Domes
Bore modifications are available for all our domes, bore size cannot exceed the diameter listed for each dome family. Because of head stud placement in some models such as the CR85 to 52mm and the KX/RM100 54.5mm the o-ring seal cannot be used because there is no room for the o-ring groove between combustion chamber and stud hole. T

Big Bore Cylinder Repair
For big bore kit modifications, machine shop services, or tuning recommendations. See our other website www.lukesracing.com  or call (734) 648-0103

Short o-ring life
Domes that have been damaged, over heated or detonated may lose their ability to make a good mechanical seal. This will cause poor o-ring life. If this is happening the dome may need replacing, also check the cylinder deck for wear or damage. In some extreme cases the head body can become deformed causing uneven clamping force which also affects mechanical seal and o-ring life. By design the dome should protrude (crush area) .05mm to .1mm outside the sealing surface of the head body. If this is not the case the head body should be replaced. For experienced builders this crush area can be corrected or increased by sanding the head body sealing surface with the dome removed on a flat surface plate with #280 grit sand paper.

Spark Plug loosens

This is from excessive vibration and is usually caused by damaged domes, poor clamping forces due to head body warping, loose engine mounts, worn