A strong present trend in racing of all kinds is to remove potentially “destabilizing” performance variables by adopting single-brand specified tires, fuel and even engines or entire motorcycles. The aim is to make racing closer and, it is hoped, therefore more attractive to a mass audience.
In AMA Pro Road Racing, the spec fuel is Sunoco 260 GTX. To get some idea of what that is, I talked with Mike Miller, who is technical and operations manager at Sunoco’s offices in southeastern Pennsylvania. One of the things I heard about the fuel from users at Daytona was that “it doesn’t make the horsepower” that some other racing gasolines do.“GTX was developed as a spec fuel,” said Miller. “It contains no oxygenates, no MTBE and no metals [lead or manganese anti-knock agents]. It’s just gasoline.”
Oxygenates include alcohols and ethers. Some sanctioning bodies ban alcohols. And the ether MTBE, after the California revelations of its persistence in groundwater, attracts lawyers.
Sunoco 260 GTX by the numbers: The important rating—Motor Octane Number, or MON— is 93+. Research is 103+, and the (R+M)/2 is 98 min.
Miller went on to say that if GTX did contain the power-boosting components that came into use during the 1990s, what would be the point?
“If everybody has it, where’s the gain?” he asked. “It just costs more.”
Some of those bad-smelling but power-boosting fuel components brought with them concern over possible health effects. Some were unstable, limiting storage life. The 260 GTX spec sheet says, “…the shelf life of 260 GTX is in excess of two years” when “…stored in opaque, tightly sealed containers where the temperature is stable.”
A look at the tech bulletin reveals that 260 GTX is heavy, with a specific gravity of .763. “We give this fuel a higher percentage of aromatics [heavy, highly anti-knock carbon-ring compounds like toluene],” said Miller, “to allow it to run with comparable compression ratios to a leaded fuel.”
I asked about 260 GTX’s sweet, buttery smell, which reminded me of fuels I used in the 1970s. “We were lucky here in our refinery,” replied Miller. “Thirty-five years ago, we took over a stainless distillation pilot plant that we now use to re-refine the alkylate [the stuff that smells so good and was long a major part of aviation and racing gasolines]. We take a middle cut and return the bottoms and tops to the normal refinery stream.” That gives 260 GTX a selective dose of the most knock-resistant “good” 8-carbon structures.
I also asked about the detailed fuel specifications issued by some race-sanctioning bodies, which set limits for lead, manganese, oxygen, nitrogen, dienes and benzene.
“It’s very difficult to meet those specs,” said Miller, “especially since we push to get to the better side [to provide more clearly legal results in case of a fuel protest]. That gets expensive. On most days, we’d like to just make fuel for normal markets.”
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