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I want the best gas! That’s the 91 octane stuff, right?

A gas price of $1.94 per gallon for regular gas is shown at a gas station Wednesday, Dec. 31, 2014, in Cleveland. The average cost of gas in Ohio has dipped below $2 per gallon for the first time in more than five years. The average for a gallon of regular gas fell to $1.99 in Wednesday's survey from auto club AAA, the Oil Price Information Service and WEX Inc. Ohio AAA spokeswoman Kimberly Schwind said that average hasn’t been below $2 since April 28, 2009, when it was $1.98. She says back then, the recession was a key factor. (AP Photo/Tony Dejak)

You want to keep your car running smoothly, so you need the “good gas”, right?  Well, it depends. It depends on whether your car has a high-compression engine, and it also depends on what you’re calling the “good gas”.  Remember high octane does not mean high quality.

Every time you pull up to the gas pump, you’re confronted with a choice. Should I use the “cheap” gas and save a little money, or use the “good” gas and spare my engine?  Maybe you’re thinking “I should use the mid-grade fuel to save money and not have to use that cheap gas”.  Based on the wear and tear on the buttons at the pump, I think most people go with the mid-grade fuel.  Actually, if you’re using the octane rating to decide which gasoline is of better quality, you might be wasting your money.  Barring any “no-ethanol” options (which are actually kind of rare), the quality of the available gasoline choices is probably the same.  The 87 octane, the 89 octane, and the 91 octane are all of equal quality.  I know what you’re thinking right now- If the 87 is so great, why do they make the 91?  Good question, and it’s not about quality.  Some engines have higher compression than others. Some high-performance engines are built so that they “squeeze” the fuel a little more than a normal engine on the compression cycle, just before the fuel is ignited by the spark plugs.  If the fuel isn’t able to be compressed that much before it detonates itself, then you’ll start to have issues.  The octane rating is how much compression the fuel can withstand before it spontaneously detonates because of too much compression.  An 87 octane fuel will detonate by itself before it’s compressed to the levels that a 91 octane fuel can withstand.  What does this mean, really? Bottom line is that your fuel will burn before it’s supposed to and you’ll probably experience a knock in your engine.

The good news for most of the drivers out there is that most modern engines are designed to run the 87 octane fuel.  Often, this fuel option is the least expensive at the pump, and contrary to popular belief, it does not bring your MPG’s down.  Another myth is that the 91 octane will offer better MPG’s in your average engine- not true.  If you’re not sure about your vehicle’s fuel requirements, check your owners manual.  Often, any special fuel requirements will be labeled inside the fuel door.

What if your high-performance, high compression engine has a knock? If it were my engine, I would baby it until that fuel can be replaced by the recommended high-octance stuff.  What if the knock doesn’t go away?  Again, if it were my engine, I’d let a qualified service techniciantake a look at it.  Woody’s Automotive Group offers a full service shop that’s able to work on pretty much any make and model.