Go to nearly any American gas station and you’ll see that there are different octane ratings. Octane ratings from 87 to 92 are there for customers, but numerous don’t know which choice is best. Reading your vehicle’s manual helps, but have you ever wondered why one octane is better for car than one more? Thanks to our friends at About.com, here’s a brief summary to help you sort out the octane rating puzzle.
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The octane rating of gasoline is a measure of that gasoline’s resistance to knocking. The infamous knocking sound comes from inefficient burning of the gasoline-air mixture. Isooctane and heptane are the points of reference when a gasoline’s octane rating is established. Isooctane has a “perfect” 100 octane rating, while heptane sits at the low end, namely zero. According to About.com, untouched gasoline has an octane rating of about 70 (70 percent isooctane, 30 percent heptane). Lead used to be the way that fuel companies cut down knocking and pinging, but current environmental standards have barred that practice, so more expensive methods of bumping the octane on unleaded gasoline have exchanged the practice.
Is it as simple as using higher octane gas?
Older car engines depended upon the carburetor to control the air/gasoline mix, so higher octane rating gas was helpful. More advanced engines became common in the mid-1980s, and fuel injectors took over the carburetor role. The standard unleaded fuel in the U.S. became 87 octane. This enabled efficient function without overwhelming the emissions system.
What about mid-grade?
A little data about U.S. octane ratings is in order here. Depending upon the state, the matching grade designation for the octane number varies. In one state, 92 octane may be premium, but in one more, it could be 90. Check your owner’s manual and watch for the octane rating on the yellow sticker at the pump.
What about premium gasoline?
If your car needs a higher octane rating, it is because you have a high-performance engine to work with. Instead of passing unburned fuel into the emissions system and catalytic converter (which happens whenever you use gasoline with too high an octane rating and can produce a rotten-egg smell), a high-performance engine uses the fuel efficiently. On a related note, some big cities with air pollution troubles might require that cars use special reformulated gasoline. Clean-burning comes from oxygen infusion with this special formulation. Simply stay away from driving with too little fuel within the tank, as that will dirty the intake valves and filters and hamper efficiency. Running within the muck destroys the fuel injector over time.
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