Should the Mistra use 92 or 95 octane gasoline?

[CodyAnn]

The naturally aspirated 1.8L Mistra engine uses 92 octane gasoline, while the 1.6T turbocharged engine requires 95 octane gasoline. These gasoline grades are officially recommended in the vehicle's user manual. In addition to checking the appropriate gasoline grade in the user manual, the Mistra's fuel tank cap will also indicate the recommended grade. Typically, the gasoline grade can also be determined based on the engine's compression ratio. Vehicles with an engine compression ratio between 8.6-9.9 should use 92 octane gasoline, those between 10.0-11.5 should use 95 octane, and higher compression ratios may require 98 octane. However, with the use of new technologies, the compression ratio alone cannot determine the required gasoline grade, as high-compression engines can sometimes be tuned to use lower-octane gasoline. Other factors, such as ignition timing, turbocharging technology, and Atkinson cycle technology, also play a role. Generally, higher gasoline grades have higher octane ratings and better anti-knock properties. 92 octane gasoline contains 92% isooctane and 8% n-heptane, while 95 octane gasoline contains 95% isooctane and 5% n-heptane. If the Mistra occasionally uses the wrong gasoline grade, simply switching back to the correct grade after use is sufficient. However, prolonged use of the wrong grade can have the following effects: For vehicles designed for lower octane, using a higher grade will not cause damage, but the increased octane rating can alter the fuel's ignition point, leading to delayed combustion. This reduces the engine's power output and thermal efficiency, resulting in poorer performance. For vehicles designed for higher octane, using a lower grade can cause engine knocking. The significantly lower octane rating reduces the fuel's ignition point, causing premature ignition during the compression stroke. If combustion occurs before the spark plug fires, resistance is created during the upward stroke. This resistance makes the engine run very unevenly. Mild knocking may only increase noise without obvious engine damage, but severe knocking indicates serious engine issues, affecting not only driving stability but also causing abnormal wear on pistons and cylinders, potentially leading to cylinder scuffing.