Should the Touran use 92 or 95 octane gasoline?

[NovaFitz]

The Volkswagen Touran 1.4T uses 92 octane, while the 1.8T uses 95 octane. These gasoline grades are recommended in the vehicle's official user manual. In addition to checking the appropriate gasoline grade in the user manual, the Touran's fuel 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, those between 10.0-11.5 should use 95 octane, and those with higher compression ratios should use 98 octane. However, with the use of new technologies, the compression ratio alone cannot determine the gasoline grade, as high compression ratios can also be tuned to use lower octane gasoline. This is because factors such as ignition timing, turbocharging technology, and Atkinson cycle technology also play a role. Generally, the higher the gasoline grade, the higher the octane rating and the better the anti-knock performance. 92 octane gasoline contains 92% isooctane and 8% n-heptane, while 95 octane gasoline contains 95% isooctane and 5% n-heptane. If the wrong gasoline grade is occasionally used in the Volkswagen Touran, simply switch back to the correct grade after the tank is empty. However, long-term use of the wrong gasoline grade can have the following effects: Using a higher octane gasoline in a vehicle designed for lower octane will not cause damage, but the increased octane rating can alter the fuel's ignition point, leading to delayed combustion in the engine. This reduces the engine's power output and thermal efficiency, resulting in poorer performance. Using a lower octane gasoline in a vehicle designed for higher octane 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 ignites, resistance is created during the upward stroke. This resistance makes the engine run very unstably. If the knocking is mild, it may only increase noise without significant engine damage. However, noticeable knocking indicates severe engine conditions, affecting not only driving stability but also causing abnormal wear on pistons and cylinders, potentially leading to severe engine damage.