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Tuning for Today’s Oxygenated Fuels

by Classic Motorsports

Posted on 9/26/2024 at 9:00 AM

Ethanol fuel pump



Many of the fuels found at today’s pumps are oxygenated, meaning alcohol has been added. You can see it right there on the pump: “May contain up to 10 percent ethanol.”

Why is the alcohol–ethanol, technically–in there in the first place? Good question. 

Oxygenated fuel provides a few benefits: It helps reduce air pollution as well as reliance on non-renewables. It can provide more horsepower, too. “Gasoline with 10 percent ethanol contains about 3.7percent oxygen,” explains Zachary J. Santner, senior specialist of quality at Sunoco. “This extra oxygen will increase the efficiency of your engine, creating additional horsepower. However, the engine will need to use more fuel volume, which is why mpg goes down.”

But will a carbureted engine automatically adjust to take advantage of that increased efficiency? Likely not, but the Sunoco Race Fuels website contains some handy info on the subject:

“In simple terms, you should start with adding enough extra fuel to offset the increased oxygen content. What does that mean? Well, let’s say you were running Supreme, which has no oxygen. If you switch to EXO2, you will need to add approximately 10 percent more fuel to offset the 10 percent oxygen content.

“The extra oxygen effectively leans out the air/fuel mixture, so you need to add enough fuel to get the air/fuel mixture back where it belongs. Actually, a safe way to introduce EXO2 to your engine would be to go even richer than you think the engine needs. Remember, engines can tolerate being rich a lot better than being lean!”

Sunoco admits that it isn’t a carburetor expert, though: “So have a conversation with your carb builder if you need to know how their carbs need to be re-jetted.”

Another useful tool to get your carburetors properly dialed in for today’s oxygenated fuel? A chassis dyno that’s equipped with a wideband air-fuel gauge and run by a competent operator.