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Understanding Octane: How to Pick the Right Rating for Your Racing Engine
From the editors of
Understanding Leaded Race Fuels
Lead was legislated out of pump fuel decades ago, but there’s still a place that you’ll find it: at the track. Adding lead to gasoline is an easy, inexpensive way to increase octane, something craved by high-compression, fast-spinning engines–especially those from the days before fuel injection.
But when faced with all of the choices, which race fuel is right for you? Zachary J. Santner, senior specialist of quality at Sunoco, notes that three products will cover most road racers requiring a leaded, high-octane product.
For more background on how octane works, see our related post: Understanding Octane: How to Pick the Right Rating
110 Octane: Sunoco’s Standard, a 110-octane fuel, has basically been around since the ’70s. Think of it as an entry-level race fuel, Santner says, “that can satisfy a pretty sporty performance build.” Define sporty? He figures roughly below these three parameters: a 13:1 compression ratio, a 4-inch piston bore and a 7000 rpm redline.
112 Octane: “Supreme is for when people are pushing things a little bit further,” Santner says of Sunoco’s 112-octane leaded race fuel. “Supreme is a little lighter and has less aromatic hydrocarbons, so it burns a little quicker.” How can you tell a fuel’s weight? Check out its specific gravity. Faster burning and increased octane make it better suited to a more aggressive setup–figure engine speeds north of 7000 rpm, compression ratios up to about 15:1, or piston bores past 4 inches.
116 Octane: High-revving, high-compression, big-block engines–picture something extreme, like a big-block Corvette, 427 Cobra or Ford GT40–need a lot of octane plus a lightweight fuel that will provide a fast flame front across those large-diameter pistons. A 116-octane fuel like Sunoco’s Maximal is designed for these situations, Santner explains.
What About Too Much Octane?
Too much octane won’t hurt anything or cause power losses, Santner says, noting that if you’re debating between 110- and 112-octane fuels, the 112 might be the answer since it would allow more ignition timing. “When you get to the higher end of Standard being the right fuel for you, you might want to look at Supreme,” he says. The prices for 5-gallon pails are close, too: about $95 for Standard and $100 for Supreme. Figure about $115 for 5 gallons of the 116-octane fuel. And we should note, prices drop when purchased by the drum or at a pump.
