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If the manual recommends premium, you get premium. A couple bucks more a gallon is cheaper than fixing potential engine knock, don’t be cheap
Depends on the engine specifically, but in general, higher compression engines require higher octane fuel to avoid engine knock. Higher octane fuel requires more compression to ignite.
The engine computer can detect if the car is running on low-octane fuel and adjust the mixture to avoid knock, but you’ll take a hit on performance and fuel economy.
Which octane is recommended? If you’re between 89/91/93, 89/91 is probably fine. I probably wouldn’t run 87 and definitely wouldn’t use 85. Personally I just use 93 - the difference in cost per fillup just isn’t that substantial. Note that the specific octane ratings available depend on which state you’re in, which is why I wrote that the way I did.
No benefit to running higher grade fuel in engines designed for regular. Won’t hurt it, will just cost more money.
In fuel injected enhines (every car built in last 20 years), you can ssfely put in the cheapest gas. Car makers always recommend the highest octane because it has slightly more power. I raced cars (carbureted) and got caight up in the winter and summer differences with a friend that was a petrochemical engineer at a refinery. Ready for the gas nerd out session?
Hydrocarbons are just chains of atoms. Small chains are gases like methane. A little longer like 8-16 are liquids like gas and diesel fuel. Longer still and you get sludges and eventually petroluleum jelly. Yes that lubricant you put on your baby's tushy was dead dinosaurs.
For liquids, shorter chained liquids burn faster, but this isnt as useful for power as most of the pressure wave is when the piston is still high in its cycle. Too long and the pressure wave is too late and the piston is near the bottom. There is an ideal length of chain that burns just right at about a length of eight.
Octane rating is a power rating comparing the power of a particular blend of lengths to a pure 8 length chain, i.e. octane. So, an 87 octane rating has 82% of the power of pure octane. 92 octane is 92%. So if you put in 87 instead of 92, you lose about 5% of your rated power.
Some race tracks have 110 octane fuel available which can give a nice bump up in horsepower from pump gas 92. (+18%!)
Knocking used to be a problem with carbeureted engines. Knocking is just the gas burning too fast ( like race gas can do if not accounted for). All fuel injected engines have a knock sensor that detects knocking and slightly retards the timing of the spark so that the pressure wave hits at the right time. You can even just put in race gas in a fuel injected engine and it will quickly adapt.
Like everything in life, this can get more complex with valve timing, engine speed, etc.
So, yes save some money with cheap gas.
Was based on 15 gallons @ ~40c premium to regular. You can get a RAV4 and use regular gas - you’ll save a lot on maintenance and it’ll probably get better gas mileage. 🤷🏻♂️
Completely unnecessary! In older cars there used to be issues with engine knocking, but has been solved with electronics. Lower octane can produce lower power, but usually can't tell. I use 98 in the race cars, and 87 anything road (including a Ferrari & McLaren)
If you can’t feel the rev hesitation between 87 and 91, I doubt you ever drove a Ferrari
I’ve owned both (Lexus, Volvo). The dealer in both instances described how the engines are manufactured differently and some require a higher octane to function. Cutting corners on those, including adding aftermarket octane products to regular is not recommended and very risky. While they “recommend” on some models, like the RX350 I owned, the dealer explained that it is not necessary but is more of a perception of the brand itself. While some see recommended and required as the same I would say that this is what the gasoline companies are counting on. High octane is specific to some high performance engines but not your “daily driver”. As long as you follow the requirements and take care of the engine you’re good.
Higher compression and especially modern turbocharged engines run more efficient with high octane gas meaning better mpg, so it somewhat evens out the higher cost of premium.
No harm to the car at all in using 87. You will loose a few HP (especially in hot weather) and a few mpg.
Since you mentioned Audi I can give you the specific details.
Older Audis asked for premium and made no mention of a lower grade. These engines were designed for premium. 87 would work but the car had to make adjustments to prevent damage. (Retard ignition timing, cut boost)
New Audis like what you mentioned are the opposite - they are actually designed to be totally happy on 87. When you put in premium the car will make enhancements to take advantage of it (advance ignition timing, maybe increase boost)
The annual cost difference is likely a few hundred bucks.
Depends on gas prices, fuel economy and mileage, but filling with only 91 or higher octane costs me roughly $300 more per year