The standard compression ratio for Opel Corsa 1.4i engine is 10.5:1. However, it's important to note that the compression ratio can vary depending on the model year, engine modifications, and other factors. As a general rule, the compression ratio refers to the ratio between the uncompressed volume inside the cylinder and the compressed volume when the piston is at its highest point. A lower ratio can result in less power, while a higher ratio can lead to higher power output but may require the use of premium fuel and can increase the risk of engine knocking.