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De-stroked crankshaft
| Description | : | The math was easy. 67mm x 42.5mm bore and stroke = 599cc. 67mm x 40.0 = 564cc. Perfect. APE handled de-stroking the crankshaft. Carrillo supplied custom +1.25mm rods, and JE made pistons for me to get back as much compression as we could. (the CR went down due to the smaller cylinder volume vs. same combustion chamber volume) I get asked a lot: "Why not just sleeve it down?" The simple answer is, the valves would then hit the cylinder walls. Yamaha did a good job of shoving in the biggest valves possible within a 67mm bore. To sleeve it down, the valves would have to be downsized. That's not good for airflow. Reducing the stroke offered many benefits. Higher bore/stroke ratio, better rod/stroke ratio, and lower piston speed for a given rpm. So, that's the direction I went. |
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