A 2004 Ford GT prototype that isn’t road-legal and has its top speed capped at just 5 mph (8 km/h) failed to sell at an online auction as it didn’t match the reserve despite attracting a $500,000 bid.

This Ford GT is known as Confirmation Prototype 1 and carries serial number 00004. It was used by Ford for emissions testing and road certification purposes.

As this was a development prototype, it looks a little different from most other GTs out there. For example, it has a port on the passenger seat for testing different grades of fuel, experimental exhaust pipes, an exposed rear bumper, and a bare aluminum headliner. It also features the signatures of the car’s development team, including Carroll Shelby, Bill Ford, Camilo Pardo, and Fred Goodnow, the Bring A Trailer listing reveals.

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The interior of the GT prototype is similar to production models but does have a few quirks. Key features include leather-wrapped Sparco bucket seats with exposed carbon fiber backs and aluminum ventilation grommets. There’s also a CD stereo and a steering wheel that uses the airbag of a Mustang and the steering column of a Ford Windstar minivan.

Like the road-going car, the prototype is outfitted with a 5.4-liter supercharged V8 engine coupled to a Ricardo six-speed manual transaxle driving the rear wheels through a helical limited-slip differential. Documentation reveals the car has been driven 1,212 miles (1,950 km) and the engine has 217 operating hours under its belt. Like we mentioned earlier, a Ford-installed chip limits the car to 5 mph (8 km/h), although it is claimed in the comments that it can be unlimited and run at full power.