The standard four-cylinder turbocharged 2015 Ford Mustang will be called the EcoBoost, according to a leaked order guide. Many had hoped for a return of the SVO moniker. But could Ford be saving the SVO badge for an as-yet-unannounced version?

MUST SEE: 2015 Ford Mustang Order Guide Reveals 'EcoBoost' Name, Performance Package Info

It’s possible. As this video from Mustang6G demonstrates, a prototype with modified exhaust and a markedly different engine note has been spotted in testing. It looks a lot like the 662-horsepower Mustang GT500, but it sounds completely different. The car in the video above also differs substantially from the potential 2015 GT350 prototype spied earlier this year.

Suppositions as to what’s going on under the hood include everything from a hotter four-cylinder turbo car to a V-6 to unicorns dancing on the head of a pin.

Ford has thus far been rather close-mouthed about the four-cylinder Mustang and potential performance variants, though we know the standard Mustang EcoBoost will offer an optional performance package with track-rated upgrades. It’s possible this could merely be a testing mule for those upgrades.

The 2015 Ford Mustang goes on sale this fall, so we may have to wait several months to know exactly what’s going on. Keep up to date with all of the latest Ford Mustang news here.