I've noticed on some pics that some of you have what looks like strips of rubber between your fins. What's the purpose? I would think it would slow airflow around the fins and make the engine run hotter?
One of the functions is to dampen vibration that can lead to cracks and chunks of fin breaking off. Motorcycle factories like Yamaha and Kawasaki have used plastic disc installed between the fins to help prevent that problem.
In some instances they "shot peen" areas to slow down the formation of surface cracks that can lead to such failures.