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13 The biggest difference with the Kaase head is the elimination of the “semi-hemi” combustion chamber design. In its place is a more conventional, “fast burn”-type chamber that is more compact than the original design yet still voluminous at 85 cc’s. A quicker, more complete combustion is achieved with this chamber design, which boosts power. The valve location and valve sizes are essentially the same as the original Boss 429, with the intake valves marginally larger.