Premium Fuel User? You Could Just Be Wasting Money
If you're putting in premium gasoline in a car that doesn’t require it, you're not really getting the additional power and mileage or even the cleaner engine that you're looking for. In short, you're just wasting money. Yes, premium gas is no doubt a better fuel than its cheaper counterparts, but it takes the right engine to earn the benefits that it promises.
As a general rule of thumb, if your car has a fairly common compression ratio such as 8:1, you should simply ditch the premium and go for low octane fuels instead. Engines with lower compression ratios handle lower and higher octane fuels the same way. This means that regular fuel will burn properly, and so will premium fuel, so there’s really no reason why you should spend the extra cost.
On the other hand, if your car’s compression ratio is above 11:1, or if it’s turbocharged or equipped with direct fuel injection, then by all means, enjoy the perks that premium fuel affords.
Most modern engines have a specific compression ratio, which represents the ratio of the available volume in its combustion chamber for fuel from its largest to smallest capacity (re: when the piston is at the bottom or top of the cylinder, respectively). Car makers will often specify the compression engine in their cars, along with type of fuel that the vehicle should use. Information on the latter is usually located on the fuel flap. So if it says to use only 91RON (RON is short for Research Octane Number), then it would be a mistake for you to run a lower octane on it.
Why is this the case, you may ask? This is because higher compression engines run the risk of 'knocking' when fed with lower octane fuels. Their cylinders are designed to create more pressure, and consequently, more power from the fuel. Drivers who ignore manufacturer's instructions to use premium unleaded are willingly shortening their engine’s lifespan.
Unfortunately, if your engine is tuned to run on regular gas, then pumping premium does nothing but part you with your hard-earned money. For your wallet's sake, don't waste money buying premium gas if your vehicle doesn't require it.