Fuel Facts: 93-Octane Not Enough? Solutions Exist

Sponsored article presented by Sunoco.


History: Lead is an inexpensive, easy way to add octane to gasoline–and that octane prevents knock and pre-ignition. In 1973, though, the EPA demanded that lead be phased out of street fuels. The reason was simple: Lead in fuel creates pollution in the air. Cars were detuned to deal with the fuels of the day.

Additives: Pour-in-the-tank octane boosters line the shelves at corner auto parts stores, but as Sunoco Race Fuels Technical Specialist Zachary J. Santner notes, those come with a few caveats. First, many additives promise gains in terms of octane points, but be aware that 10 octane points equal just one octane number. Secondly, some octane boosters contain methylcyclopentadienyl manganese tricarbonyl, a compound that does effectively raise octane in large quantities but is often only a small component of the additive. Plus, it degrades in sunlight.

Modern Option: The current market offers a wide range of high-octane race fuels, but many technically aren’t legal for street use. An example of one that does qualify for street use? Sunoco Race Fuel’s 260 GT, with the name recalling the brand’s high-test gas of days gone by. Today’s 260 GT carries a rating of 100 octane; some stations offer it at the pump, but it’s also available in 5-gallon pails. (And for folks operating under CARB rules, Sunoco offers a similar product called SS 100.)

Mixology: Don’t quite need 100 octane? Simply mix 260 GT with street fuels to achieve the required octane, Santner says, adding that 260 GT’s extra octane won’t hurt anything: “It won’t make the engine burn hotter.” When mixing fuels, he continues, the final octane number is simply an average of the final mixture, taking into account the percentage of each fuel grade. For example, a 50/50 mix of 260 GT and 93-octane street fuel yields 96.5 octane.

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DaveD New Reader
8/27/20 3:18 p.m.

I collect vintage motorcycles, some of which have high compression ratios, others which do not but definitely run better on fuels more closely resembling their diet when new than what comes out of the premium pump today. These machines are mostly British, and include BSA, Triumph, Norton, Matchless, Velocette, Sunbeam and some old BMWs and Harleys as well.

For many years, I've used VP 110, which is just one of many blends offered by VP Racing Fuels. VP110 is 110-octane leaded fuel (they have unleaded as well, in various octane ratings), characteristically pinkish in colour and even smells like gasoline used to smell! 

Long ago, I experimented with the appropriate mix ratio, as I knew I did not need 110 octane, and at around $15 a gallon (available in blue 5-gallon drums), it was pretty pricey to fill even a two- or three-gallon tank.

After trial and error, I found that 25% VP110, mixed with 75% pump premium gave me the most benefit and efficacy in the vintage machines. Higher proportion of race fuel and the differences are minimal, if noticeable at all. Less, and you're not getting the full benefit. 

I have several blue cans in my shed. One is the newest can of VP110, one is pump premium (and clearly marked as such) and one is labeled "Mix." I don't premix a lot ahead of time; no need to do so unless you're riding very frequently.

The difference in how the bikes run is amazing. They start easier. Their throttle response is almost instantaneous—clearly superior to running on straight corn meal. And they can pull long uphills under load on hot days without knocking and pinging. Torque is improved. They also run cooler. In summary, they are happier machines and more fun and rewarding to ride.

How this translates to older cars that are sensitive to their fuel mix, I'm not sure. 

Oh, one last thing. When you buy such leaded fuels from a speed shop, you need to sign a waiver that the vehicle won't be operated on public roads. Some ask what competition event you're planning on attending, place and date. I'm not advocating that anyone who might consider operating said vehicle on the road misrepresent anything here, or makes up a fictional offroad event, with a random date and place, sponsored by a fictional organizing body. 

Keep the shiny side up!

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