2015 Ford Mustang EcoBoost loses big power on 87 octane

The 2015 Ford Mustang with the 2.3-liter EcoBoost four-cylinder is a pretty potent package on paper. With 310 horsepower and 320 pound-feet of torque, it boasts better performance numbers than the 3.7-liter V6, but with better fuel economy as an added benefit.

However, if you're in the market for one of these boosted 'Stangs, you should probably keep in mind that it really prefers to gulp premium, 93-octane fuel. It can drink 87-octane swill in a pinch, but you're going to find significantly less power underfoot when pulling away. While it's not shocking that the ponies are dialed back with a lower grade of gasoline, an alleged page from a Ford training manual obtained by Mustang 6G purports to show just how much power is lost, though.

According to this document, the 2.3-liter EcoBoost makes 275 horsepower and 300 pound-feet of torque when running on lower octane fuel. That's a substantial reduction of about 11.3 percent compared to when the engine drinks 93 octane. Interestingly, according to Mustang 6G, that finding was a bit better than expected, because a Ford engineer reportedly said power would be down about 13 percent without altering peak torque.

In speaking with Autoblog, Paul Seredynski of Ford powertrain communications, objected to part of this document. While he couldn't confirm the specific losses listed for the Mustang EcoBoost, "torque remains unchanged" with lower octane gasoline, Seredynski said. He speculated this training manual page was "possibly from before the engine was certified" and therefore showed incorrect figures. Serendynski did confirm that the automaker recommends using 93 octane, and like all modern engines, the software adapts if it's lower. "Peak power would be reduced" by using a lesser grade, he confirmed.