When I open up the door to my gas cap, there is a large sticker on the inside that says "Premium Fuel only." But do I really need premium fuel? There are some out there who believe that premium fuel is a conspiracy to get the weak minded to buy more expensive gas. Certainly, there are a lot of websites that back this claim up.

First we have to define the word "necessary." Do we mean premium gas is necessary or my engine will blow up? Or do we mean premium gas is necessary for optimal performance of your car?

The first question, is premium gasoline necessary for protecting your engine? The answer is probably not.

An octane rating measures the fuel's resistance to ignition. So, I higher octane gas takes longer to ignite than a lower octane gas. If timed right, this later ignition can equal more compression in your cylinder, which translates to more power to your wheels.

So what happens if I put low octane gas in my car? As expected, the fuel will ignite early (this is called pre-ignition) and cause the engine to knock (aka ping). The knock sounds like a little pinging sound like a bit of metal smacking against the engine block. What is actually happening is that the gas is igniting from the center of the chamber from the spark plug, but also igniting from the outside of the chamber by itself before the first flame ignites all the fuel. So you get two explosions instead of one, a lot more pressure than the chamber is designed for, and you wear out your engine.

Modern cars are just as susceptible to knocking as old cars, but their advanced computers have protection built in. A knock sensor will listen for pinging and automatically adjust the timing in the engine to accommodate. Your engine may knock a little bit, but your computer will correct and no damage will be done to your vehicle.

Sometimes the timing cannot fixed by the car and you will get knocking anyway. My last car had a problem with pre-detonation that the computer couldn't fix and was only mildly helped by using higher octane fuel. I've also ridden is several cars with pre-ignition problems that the computer can't fix for whatever reason. But that's besides the point.

So, back to our original question. If high octane fuel necessary? If by necessary you mean "necessary for the engine to operate" the answer is no. You engine will operate fine on just about any commercial octane you put in it.

So why the different choices? Why would you ever pay for high octane?

Remember how I said the engine adjusts itself? Well it was tuned a certain way to begin with for a reason. Remember advanced timing = higher compression = more power? So when you de-tune your engine, you're getting less compression, and therefore less power. If this wasn't true, there would be no reason for advanced timing in the first place.

On a car like mine, according to car and driver, using low octane fuel will cost me ~10hp. If I wanted my car to perform like a Honda Civic, I would have just bought a Honda Civic.

I have a friend who runs something like 130 octane in his car on the track. He could tell you all about the benefits of high octane fuel. Anyone who drives on the track will tell you the same thing. No rational bugatti Varion driver would put low octane fuel in their car (in fact, they wouldn't even use high octane - they're in a class all their own - more like 111-118 octane).

So, back to the original question: Is high octane fuel necessary? If by necessary you mean necessary for you car to run at optimal performance than the answer is yes.

Of course, that only applies to you if you drive a car that says it needs high octane fuel. Putting high octane in a regular old car isn't going to improve performance, and in fact you will end up just wasting your money and probably getting less performance due to the fuel igniting too late in the cycle.

So, the final answer - is it necessary? I guess it depends on what you want. If you want to get what you paid for out of your sports car, than yes, use premium. If you want it to run like a Civic, then you don't need to worry about ruining your engine by running low octane in it.