Does the octane in the manual match the pump? | Fuel Facts | Articles

Does the octane number in your manual match the one on the pump? | Fuel Facts

When it’s time to gas up, the recommended fuel is right there in the owner’s manual. But what if it’s not so simple? Case in point: our 1984 Porsche 911. Its owner’s manual recommends 96 octane, with a minimum of 91 octane.

Does that mean Porsche recommends 96-octane race fuel? No. “Pumps in the U.S. are AKI,” explains Zachary Santner, senior specialist of quality with Sunoco. “The rest of the world uses RON.”

RON, short for Research Octane Number, is just one way to measure octane–and it’s pretty much the world standard. American and Canadian fuels, however, are measured using the Anti-Knock Index, an average of RON and another octane rating called the Motor Octane Number. Generally, the RON figure is 4 points higher than the AKI number.

Confused yet? Probably. Here’s the takeaway: Figure out which octane scale your fuel recommendation uses so you can grab the right nozzle. For example, our Porsche’s recommendation is in the form of a RON figure, so we should look for American pumps featuring an octane rating of 92 or higher, with 87 being the minimum.

Those on the West Coast, however, need to adjust. “Depending on where you are in the country, 89, 90 and 91 could all be considered a premium non-ethanol fuel or the best the local terminal can get,” Santner explains. “On the West Coast, 91 octane–10% ethanol–is the highest-octane pump fuel. This is most likely 89 non-ethanol gasoline mixed with 10% ethanol.”

But what about the fact that our car was built before today’s ethanol-enhanced fuels became the norm? “In my professional opinion, you should use a non-ethanol fuel,” Santer continues. “The car was not designed with ethanol compatibility in mind, so go easy on the fuel system [by using] a 100% gasoline. Non-ethanol fuel will have better storage properties because it won’t have issues with water and humidity.” Non-ethanol fuel costs more, but that’s not a big issue considering how little this car is driven annually.