This document summarizes the design of a 400cc racing bike engine. It calculates the swept volume as 373.197 cm^3 based on the piston diameter of 8.9 cm and length of 6 cm. The compression ratio is specified as 11.3:1, yielding a clearance volume of 33.026 cm^3. The mechanical efficiency is calculated as 72.59% based on a brake power of 25.74 and indicated power of 35.46.