Bore: 90.95mm Compression: 10.5:1 Compression Sizing: 1.00mm OversizeSPECIFICATIONS. Displacement: 508.94cc. Bore - Standard: 89.00mm. Bore - Actual: 90.00mm. Bore - Oversize: 1.00mm. Stroke: 80.00mm. Cylinders: 1. Compression Ratio - Actual: 10.5:1. Note: Cylinder boring required. ITEM CONTENTS. 3544XC - 90.00 mm Ring Set. CW21 - ROUND WIRE PIN LOCKS 21MM (PAIR). S527 - PistonPin 21mm x 2.126in. NonChromed SW All Wiseco Pistons are forged from high silicon, low expansion aluminum which offers superior strength, reduced weight, improved heat transfer, and longer life. Diamond turned finish from one of the many CNC computer controlled turning centers guarantees you a perfect finish with no size variation. Wiseco pistons can be installed in any of todays cylinder bore compositions. Wisecos state-of-the-art computerized manufacturing facility is dedicated to supplying both the high-perfomance racer and recreational enthusiast with the finest forged piston available in todays market place.1982-1983 fits HON FT500 Ascot 1982 fits HON XL500R 1979-1981 fits HON XL500S 1979-1980 fits HON XR500 1981-1982 fits HON XR500R