Should T-equipped cars use 92 or 95 octane fuel?

[DelaneyLee]

According to the official vehicle manual recommendation, all T-equipped models should use 95 octane gasoline. For T-equipped models, besides checking the appropriate gasoline grade in the vehicle manual, you can also find this information on the fuel tank cap, which will be clearly marked. Typically, the fuel grade can also be determined based on the engine's compression ratio. Vehicles with a compression ratio between 8.6-9.9 should use 92 octane gasoline, while those with a compression ratio between 10.0-11.5 should use 95 octane gasoline. However, with the application of new technologies, the compression ratio alone cannot determine the appropriate gasoline grade. High compression ratio engines can still be tuned to use lower octane fuel because factors other than compression ratio also play a role, such as ignition timing, turbocharging technology, and Atkinson cycle technology. Generally, the higher the gasoline octane number, 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 a T-equipped model occasionally uses the wrong gasoline grade, simply switch back to the correct grade after consumption. However, long-term use of the wrong gasoline grade can have the following effects: For vehicles recommended to use lower octane fuel, using higher octane gasoline will not cause damage, but the increased octane rating will alter the fuel's ignition point, leading to delayed combustion in the engine. This means both the engine's power output and thermal efficiency will decrease, resulting in poorer performance. For vehicles recommended to use higher octane fuel, using lower octane gasoline can cause engine knocking. Because the octane rating is too low, the reduced ignition point may cause premature ignition during the compression stroke. If combustion occurs before the spark plug fires, resistance will arise 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, and in severe cases, cylinder scoring.