Most higher end cars now days seem to require premium gas. i was wondering if it is really necessary so long as you are willing to give up some of the cars performance. The cars in question are the Acura TL, Audi A6, and the BMW 335i.
The key word is REQUIRED vs RECOMMENDED in the manual or on the fuel door.
This question has been answered quite a few times. If the owner’s manual says that the engine requires premium fuel, then premium fuel needs to be used. While the computer system will somewhat adjust the engine for a lower octane, what happens is that the ignition timing is retarded. Gasoline mileage will suffer and under certain conditions the engine will run hotter with the retarded timing. Premium is required in these cars to prevent pre-ignition (the engine knocks under load because the fuel mixture ignites too quickly. The higher octane lets the fuel mixture burn more slowly). This would damage the engine if the spark is not retarded. My guess is, on these high end cars, that the use of non-premium fuel may lower the mileage so that it is actually more expensive than to use the required premium fuel let alone possible engine damage.
A secretary in my department office recently bought a used MiniCooper. She uses premium as required and claims that with the mileage she gets, as well as the performance, the extra cost of premium fuel is a small price to pay.
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In addition to giving up some of the car’s performance potential, you will also get lower gas mileage if you use regular in a car designed to run on premium. I was skeptical of the need for premium gas in my car, whose manual merely “recommends” premium, rather than stating that premium gas is required. Several times I have compared the difference between using regular and premium gas in my car, and the drop in gas mileage with regular gas (about 1.5 mpg less), as well as the loss in acceleration, convinced me that it just wasn’t wise to “cheap out” by using regular gas.
An observation that I have made is that when an engine starts pinging at high loads, like when climbing a hill, the pinging goes away if you close the throttle a little. So, if you always drive like there is a raw egg between your foot and the gas pedal, keeping the manifold vacuum high all the time, your engine will never miss premium gas.
I have often thought about why nobody makes a car with injectors that inject regular gas whenever the manifold vacuum is high, (most driving) but switch to a second set of injectors that inject premium from a second tank when the manifold vacuum is low, like when you are passing someone.
It never ceases to amaze me that someone can go out and buy a 45k car. And then debate on whether or not to use premium fuel on a high end car. Those vehicles are for people of means. If you’re having to debate on what fuel to use. Then those vehicles are probably not for you.
The amazing thing to me is the price increase of getting regular vs premium is at its lowest ever. It is only 5-7% over regular. People gladly paid 10-20% extra for it when fuel was $1-2/gallon but now want to quit and question the need.
I will admit in my vehicle that requires premium that I occasionally put in regular if tank is half full or better. It requires 91 octane and in my area premium is 93 octane.
I have often thought about why nobody makes a car with injectors that inject regular gas whenever the manifold vacuum is high, (most driving) but switch to a second set of injectors that inject premium from a second tank when the manifold vacuum is low, like when you are passing someone.
Probably because the cost of everything that you would need to do that would exceed any savings you would see.
As an exercise: Figure out what the cost of the injectors, tank, pump, sensors, plumbing, and whatever else you would need to do this would be. Then figure out how many gallons of gas that would upgrade from regular to premium assuming a reasonable markup.