No, THIS is a myth. I'm a mechanic and car enthusiast, and have done extensive testing with my own sedan, sports car and SUV. Using higher octane gas gives me as much as 2 mpg better mileage in my cars. The power and response is better, and the injectors stay cleaner. The difference in acceleration in our sedan and SUV is very noticeable. Just running a tank of premium through our SUV has caused the "check engine" light to turn off on two occasions due to the cleaner combustion and higher efficiency. The new Hyundai Genesis sedan is rated 15 horsepower higher if premium fuel is used, though it can be run on regular grade. Premium fuel burns more efficiently and with more power.
I recommend running a tank of mid-grade or premium through ANY car at least every ten tanks of gas, as well as a can of good injector cleaner to keep the fuel system clean. I even burn premium fuel in my gas-powered lawn mower and yard care equipment. I think that is why one of my lawn mowers survived for 29 years without an engine problem.
"No, THIS is a myth. I'm a mechanic and car enthusiast"
I'm the person who wrote the comment you're responding too. I'm also a mechanic and car enthusiast. I've tried running higher grade fuels in cars designed for regular, and to be honest, found absolutely no difference in any kind of performance aspect. As for keeping the injectors clean, that's why I just run some fuel system cleaner through my car every few fill-ups.
By the way, try justifying spending 15 cents a gallon more for an extra 2 MPG. Any MPG increase you're getting from running premium fuel in a car designed for regular is immediately offset by the price difference of premium and regular. It just doesn't make sense to be putting premium in a car designed for regular.
"It just doesn't make sense to be putting premium in a car designed for regular."
Only if you don't want more power, a smoother running engine and better mileage. All of these things are a result of burning higher octane fuels in ANY engine. Why do you think there are notices on gas pumps that contain ethanol that warn you that you will get less mileage? It's because ethanol decreases the combustibility of the gas, just as a lower octane rating does. "Designed for regular" is a sales gimmick used by the auto industry to sell cars. Yes, the car WILL run on regular. If you are lucky it MIGHT not even knock. But higher octane fuel adds power, smoothness and burns cleaner.
I've been running regular in all my cars. All my cars have been DESIGNED for regular. None of them knocked because of it. You WILL NOT get significantly better mileage by filling a car designed for regular fuel with premium. 2 MPG is NOT a significant enough increase to justify the large price difference between regular and premium. Maybe gas is cheaper where you are, but where I live regular costs $2.59 a gallon, while premium usually costs $2.71 a gallon. From a gas mileage stand-point (and a NOTICEABLE power-gain standpoint), putting premium in a car DESIGNED for regular DOES NOT MAKE SENSE.
As someone schooled in chemistry and physics, the argument about premium versus regular gas is a moot point. Higher combustibility ALWAYS means more efficient burning. Higher octane fuels deliver more combustibility, therefore they HAVE to be more efficient and deliver more power. It's simple. You can't ignore the laws of physics.
As pointed out in an earlier comment, Hyundai rates the new V-8 Genesis sedan at 15 more horsepower using premium rather than regular. You CAN run regular in them, but the power (and fuel mileage) drops very significantly. Of course you can get away with using regular in most cars today, but you WILL save fuel and have noticeably more power if you use higher octane fuel. Why do you think drag racers use nitrous oxide?
Every one of my late model cars has in the owner's manual 93 octane. Even our Honda VTEC 3.2 required it to prevent detonation. One of my boats, a Boston Whaler with just a 50 HP, also runs 93 octane as well. Ignites better and runs better.
Ethanol is a real concern. If you do not drive your cars much, I add Startron to address the ethanol breakup. For winter storage I use Stabil. I like to use Techtron in the spring. I add ZDPP on my classics with Castrol regular oil because of the lack of lead in the fuel. Late models, I use synthetic with high grade filters.
Lastly, my Harley Davidson Fuel Injected Night Train runs 93 Octane gas. Keeps you busy staying on top of all this, but I have yet to ever buy a new engine.
Read your owners manuals; you may find you are putting in the wrong octane. Get on the throttle or pass someone, and you may detonate an engine on ones that you would be surprised require it. Correct fuel and oil is a lot cheaper than a new engine. Some of the new ones, with cold passages in the blocks with poor designs, are failing in spite of your good efforts. Save oil change filter records, and hope you don't have to fight it.
I have a 4.0 liter 2006 Taco, and gas quality makes a difference in it. I run mid-grade most of the time, and put a bottle of injector cleaner through it about every 4 months. I can definitely feel it bog down with a lower quality gas, especially when I'm passing a slowpoke on the highway.