Pistons are tapered somewhat because high temperatures cause the top of the piston to expand more than the skirt area. For this reason pistons are measured in the skirt area rather than across the crown. Also, pistons are cam ground; that is, they are oval-shaped because they expand more in the direction of the pins.
Wiseco’s detailed skirt shapes and profiles are very specific to each application. Variable cam programming software developed in house allows Wiseco to produce high-performance shapes unique to only Wiseco.
The skirt shape (barrel/cam) is one of the most functional areas on the piston, and provides stability and smooth operation in the cylinder bore. Stability is important for proper ring seal, reduced friction, and quiet operation.
Each skirt shape is designed for a specific running clearance, based on coefficient of thermal expansion of the piston alloy. Some forging alloys expand more than casting alloys, but each Wiseco piston is designed with the proper installed clearance to produce the most power, least wear, and best seal at running temperature, for each application.
Comparing installed clearances on cast vs forged parts is not indicative of the running clearance at temperature. Wiseco engineers have a strong background in all forms of racing applications, and produce the best shapes and designs in the industry.
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