Should the Audi RS5 use 95 or 98 octane gasoline?
3 Answers
The Audi RS5 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 user manual, you can also find it indicated on the fuel tank cap of the Audi RS5. 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 those with a higher compression ratio should use 98 octane gasoline. However, with the application of new technologies, the compression ratio alone cannot determine the required gasoline grade, as high compression ratio engines can also be tuned to use lower octane fuel. This is because factors other than compression ratio, 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 RS5 occasionally uses the wrong gasoline grade, simply switching back to the correct grade after use is sufficient. However, prolonged use of the wrong gasoline grade can have the following effects: For vehicles recommended to use low-grade gasoline, using a higher grade will not cause damage, but the increase in octane number can alter the fuel's ignition point, leading to delayed combustion in the engine. This results in reduced engine power and thermal efficiency, manifesting as poorer performance. For vehicles recommended to use high-grade gasoline, using a lower grade can cause engine knocking. Due to the significantly lower octane number, the gasoline's ignition point decreases, causing premature ignition during the compression stroke. If combustion occurs before the spark plug ignites, resistance will arise during the upward stroke. This resistance makes the engine run very unstable. If the knocking is imperceptible, it only increases noise without obvious engine damage. However, noticeable knocking 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 driven an Audi RS5 for two years, and this car strictly requires 98-octane fuel as clearly stated in the manufacturer's manual. High-performance engines with high compression ratios need higher-octane 98 fuel to effectively prevent knocking. Last time I was in a hurry and used 95, I immediately noticed slight engine shudder during acceleration, and fuel consumption increased by half a liter. Although 95 can work in a pinch, only 98 unleashes the full potential of this 450-horsepower V6 engine. Long-term use of 95 may lead to more severe carbon buildup and shorter spark plug replacement intervals. During every maintenance check, the mechanics compliment my engine's excellent condition - all thanks to consistently using 98. If you want to save on fuel costs, you should've chosen a regular A5 instead. When you buy an RS5, you should feed it premium fuel.
As an automotive engineer, I can responsibly say that the RS5 must prioritize using 98 octane gasoline. When the twin-turbocharged engine operates above 5,000 RPM, the cylinder temperatures are extremely high. 98 octane fuel contains 3% more isooctane than 95 octane, offering significantly better anti-knock performance. I've tested cars running on 95 octane, and the ECU automatically retards the ignition timing to adapt, resulting in approximately 5% power loss. While mixing 95 octane is acceptable for short-term emergencies, long-term use can accelerate carbon deposit formation, especially in direct-injection engines' fuel injectors. Additionally, 98 octane gasoline typically contains more detergents, which help protect the high-pressure fuel pump. Although the price difference per tank is a few dozen yuan, considering potential long-term repair costs, it's still recommended to use 98 octane.
