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Pistons

The diagram below show piston terminology.

Information required to calculate Piston to Cylinder wall clearance and Piston ring end gap.

Special Clearance Requirements of Pistons

A close fitting piston rocks less, supports the rings better, and seals the engine for maximum power.

Special Notice on Top Ring End Gap
Pistons make more HP by reflecting heat energy back into the combustion process and, as a result, the top ring runs hotter and requires end clearance. Increasing ring end gap does not affect performance or oil control because normal end gaps are realized at operating temperatures. Failure to provide sufficient top ring end gap will cause a portion of the top ring land to break as the ring ends butt and lock tight in the cylinder. The broken piece may cause further piston or engine damage. Safe top ring end gaps can be found by multiplying the bore diameter by the appropriate ring end gap factor from the clearance chart below.

Example: 4" bore "Street Normally Aspirated" = 4" bore x .0065 = .026 top ring end gap. NOTE: Second ring end gaps do not need extra clearance. Dyno and track testing has shown that 34 degrees or less total ignition timing makes the best HP and time. Excessive spark advance, lean fuel mixture or too much compression for the fuel and cam used will make heat sufficient to butt piston rings with as much as .060" ring end gap. The entire top land can expand enough to contact the cylinder walls, when close to melt down temperatures are reached.