Should you use fuel additives? Do you have options if 93 octane isn’t enough? How much ethanol is really in that E85?
If you’ve asked yourself any of these questions, it's been answered by Sunoco technical specialist Zachary Santner as part of our Fuel Tips and Fuel Facts series, which you can read in their entireties below.
Fuel Tips from Grassroots Motorsports:
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This might come as a surprise, but one of the biggest things I learned from these is that just because it's labeled E85, doesn't mean it gas 85% ethanol.
I know, might sound like a given, but I guess I just assumed it would always have that much ethanol in it.
In reply to Colin Wood :
Our pump stickers actually say 51-85% ethanol. Later in the summer it's usually near 85% in winter it's closer to 51%
But that's not the only problem. The 15% that is gasoline can be pretty poor quality gasoline.
Hence the need to buy from a racing source. To get 85% ethanol and high quality gasoline.
That or have a flex fuel sensor measure and do the timing and fuel quality adjustments for you.
Sames, the E85 talk has been among the bigger surprises for me. "You mean that E85 can contain only 51% ethanol?"
JG had been running our Corvette on E85 from the corner station. Then we got some Sunoco E85-R for Time Trial Nats.
"So, um, what's the other 15% of that stuff?" he asked me. "Rocket fuel?"
So I asked Sunoco: The gasoline component of E85-R is almost 100 octane race fuel, not 85 octane low-grade. 
In reply to David S. Wallens :
Man, I HOPE it's not rocket fuel- that would be a terrible choice. That's just very pure kerosene- which has a pretty low octane rating. Good cetane, though.
I know it's a passing joke, but it's interesting how people think that "rocket fuel" is so potent for a gas engine.
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