Arguably the ultimate engine upgrade for the XR / NX engines. High efficiency, knock resistant, welded and CNC machined combustion chamber with matching bespoke 102mm fully CNC machined piston 10.5:1 CR (actual).
We know this air cooled engine is prone to knock, specially in hot areas and enduro races and the big bore engines suffer this undesirable situation to the worst indeed. Thats is why Honda uses a shy 8:1 compression ratio. Larger bores with high compression pistons often end up with retarded ignition timing and overrich mixtures to fight knock thus killing performance.
We developed a custom machined combustion chamber with large squish areas for faster burning and shorter flame travel , combined with a CNC machined piston with matching crown design that can run up to 11.5:1 CR with optimum ignition timing without knock (tested!).
Furthermore, we have optimized the design for a strong piston, saving material in those areas where it is not required so we have achieved a 20grm saving against another famous brand (same bore). This is very important for single cylinder engines when you want to keep the OEM crank balance factor: smoother running, less vibration, faster revving.