Should the Audi S4 use 95 or 98 octane gasoline?
2 Answers
Audi S4 uses 95 octane gasoline, which is the recommended fuel grade specified in the vehicle's official user manual. In addition to checking the appropriate gasoline grade in the vehicle's user manual, you can also find it on the fuel tank cap, which will also indicate the recommended grade. Generally, the fuel 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 gasoline, and if the compression ratio is higher, 98 octane gasoline is recommended. However, with the application of some new technologies, the fuel grade cannot be solely determined by the compression ratio. A high compression ratio can also be tuned to use lower octane gasoline because, apart from the compression ratio, other 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 number 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 Audi S4 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 gasoline, using higher octane gasoline will not cause damage, but the increase in octane number 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 in practical terms. For vehicles recommended to use higher octane gasoline, using lower octane gasoline can cause engine knocking. Because the octane number is too low, the fuel's ignition point decreases and may ignite prematurely during the compression stroke. If combustion occurs before the spark plug fires during the compression stroke, resistance will arise during the upward stroke. This resistance can make the engine run very unstably. If the knocking is imperceptible, it only increases noise and does not cause significant damage to the engine. However, if noticeable knocking occurs, it indicates severe engine conditions, affecting not only driving stability but also causing abnormal wear on the pistons and cylinders, and in severe cases, cylinder scoring.
I've been driving an Audi S4 for several years, and from an owner's perspective, let me talk about fueling. The Audi S4 is a high-performance car with a high engine compression ratio, and the official manual recommends using 98-octane gasoline. High-octane gasoline better prevents knocking—knocking is when the gasoline ignites out of the normal sequence, sounding like a rattling noise, which can damage the engine. Although 98-octane is a bit more expensive, it provides smoother acceleration and hill climbing, with quicker engine response and no jerking sensations while driving. If you use 95-octane, you might not notice a difference during low-speed city driving, but it can easily cause engine issues during high-speed or aggressive driving. Over time, it leads to more carbon buildup, and repairs end up costing more. For the sake of the car and driving experience, I always stick to 98-octane, especially since the newer S4 models come with turbocharging, making the engine even more sensitive—don’t cut corners and risk damaging the car. Regular maintenance and checking fuel quality are also important to ensure the gas station is reliable and avoid mixing in low-quality fuel.
