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In an air-cooled engine, waste heat dissipates from the cylinder, through the cooling fin, to the cooling air. This cooling air is kept moving by a cooling fan in most utility engines, and by the relative motion in moving motorbikes. However, such cooling becomes less efficient when air is not forced around the cylinder, e.g., in utility engines without cooling fans and in stationary motorbike engines. Here, the temperature may increase in the space between the fins, decreasing the heat release from the cylinder. In an effort to increase natural convection in the cylinder, and so decrease the temperature between the fins, we produced special cooling fins with slits arranged in a fixed equiangular spiral. We tested experimental cylinders, varying the fin slit widths and slit setting positions, and measured the temperature inside the cylinder to determine the heat release from the cylinder.