Can you blend fuels to get the right mix? | Fuel Facts

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Can you mix together different fuels to get what you need? In most cases, yes. “Our gases mix well with each other,” explains Zachary Santner, technical specialist with Sunoco Race Fuels.

Gas Math: When mixing fuels, a weighted average will get you fairly close, Santner explains. For example, a tankful that’s three parts 90 octane and one part 110 octane would yield approximately a 95 octane mix. But before you start grabbing nozzles, a friendly reminder that leaded fuels will harm the catalytic converters and oxygen sensors found in modern cars. 

Mixing for Octane: Most pump fuels now top out at 93 octane. That’s fine for today’s machines, but that ’60s performance car might have been built back when octane numbers found at the corner station ran closer to 100. 

If looking for a solution that’s street-legal, Santner says, you could run Sunoco 260 GT, a 100 octane, unleaded street-legal fuel.

While straight 260 GT would provide more than enough octane in this case, if less octane was needed you could save some money by cutting it with pump fuel. A 50/50 mix with 93 octane, for example, would yield about 96 octane, and you could adjust as necessary. Those headed to the track could opt to instead mix in an off-road racing fuel. 

Mixing for Storage: Today’s oxygenated fuels usually contain up to 10 percent ethanol. The ethanol helps those fuels produce more power, but the ethanol also absorbs moisture over time, especially in an older fuel system that isn’t entirely sealed. That moisture can eventually cause all kinds of problems. 

Some stations offer non-ethanol fuels, with 89 and 90 octane usually being the upper limit. Need more octane than that–like closer to 93? Sunoco offers an unleaded fuel called Optima: 95 octane and no ethanol. It’s not street-legal, the company notes, but its website adds that this fuel won’t harm oxygen sensors and catalytic converters. If stored in a sealed, air-tight container, shelf life is more than three years.

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Torqued New Reader
7/19/21 7:07 p.m.

Just curious - Why is Optima not street legal if it is unleaded and wont harm sensors or catalytic converters?

David S. Wallens
David S. Wallens Editorial Director
7/30/21 8:22 a.m.

In reply to Torqued :

Just chatted with our friends at Sunoco. Why isn't Optima branded as street legal?

Two main reasons:

It's not taxed for road use.

Rules for street fuels can vary by state and county--local regs might require ethanol, for example, in addition to seasonal blends--so it's impossible for Sunoco to say that Optima is 50-state legal. 

DaveD New Reader
8/3/21 6:22 a.m.

While I collect vintage cars, my greater passion is vintage motorcycles. My modest collection numbers roughly 30 bikes, mostly popular British (BSA, Triumph, Norton, Velocette, Matchless), and some old Harleys, BMWs,. etc). As ethenol-based fuels came into general use, many of these otherwise finely-fettled machines ran increasingly poorly (decreasingly well?). I was introduced to VP Racing Fuels by a mechanic friend and experimented with their VP110, which is a 110 octane leaded gasoline.

As an example, my 1962 Norton Atlas, a twin-cylinder 750cc machine with a compression ratio of 8:1 (after one of my rebuilds over 40+ years of ownership) was running poorly, especially on hot days, under load and two-up. "Pinking" as the Brits would say...pre-ignition. Plus blueing exhaust pipes, loss of power, oveheating maladies, etc. No amount of dialing in the timing, mixture, etc., would help. Not a happy machine.

I experimented with a blue, 5-gallon drum of the precious stuff ($11/gallon then, more like $15/gallon now). With 100% VP110, my ol' Norton ran like new—not only starting easier, but the throttle response was noticeably quicker and power so linear and reliable, I could torque my way up long uphills in top gear, two-up, on a hot Southern California day with nary a protest from the happy machine.

So I tried a 50% mixture with pump premium, considering the high running costs. Also brillaint. And so I dialled back to 25% VP110. Still a splendid result. Then 15%. At this point, I noticed a drop-off in benefit. So I locked in that 25% VP110 to 75% Pump Premium and after all these years, it's still the go-to Magic Elixir! I use it in any motorcycle that originally lived on a diet of leaded premium fuel, or whose compression ratio was increased to require such octane enhancement. VP also has non-leaded fuels and many octane ractings for a myriad of applications.

Note that this fuel is not approved for street use and you will need to fill out a form at point of purchase declaring that the machine in which it will be used will only be used in off-road (or roadracing) activities. Wink-wink.

Your mileage may vary.

~ Dave Destler

Tim Suddard
Tim Suddard Publisher
8/5/21 8:15 a.m.

In reply to DaveD :

Good ad advice and nice to hear from the founder of British Car and Bike, now Classic Motorsports magazine.

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