If you are running todays regular unleaded gas you must pay attention to compression. These new design Federal Mogul (AE) pistons are designed for modern fuels and compression. Typically installation will result in 8.8:1 compression (the original "S was 9.75:1 and would never last without special efforts). Current pistons differ from the 60s originals, improved with a "low drag" slipper skirt design and a shorter lighter wrist pin. Wrist pin height is 1.4689", top is dished 8.4cc, and they have a 4mm oil ring and two 1.5mm compression rings.