Following the debut of the Galpin Rocket last year, Galpin Auto Sports and Henrik Fisker are back with the Speedster Concept. The custom-bodied, 725-hp Mustang wears a smooth open-top design with tonneau cover. A limited number of customers looking for a more powerful, unique breed of Ford Mustang convertible have a new option.

Galpin Auto Sports has a short history of presenting crazy-powerful, Ford-based creations at Pebble Beach Concours d'Elegance. Two years ago, it showed its first coach-built supercar, beating Ford itself to the punch in reviving the iconic GT. It dropped a 1,024-hp V8 in the car, slapped some rather horrifying purplish-blue leather inside and charged buyers US$1.024 million a pop.

Galpin went on to team with one of the most respected minds in car design: Henrik Fisker. Together they revealed the Galpin Rocket prototype at last year's LA Auto Show, showing how a subtly retro-inspired custom carbon body and supercharged 725-hp tune could transform the Mustang into the "ultimate American muscle car." The company officially launched the limited-production coupe at the Amelia Island Concours d'Elegance in March.

Whether or not you want to award the Rocket that "ultimate" title or reserve it for one of the even more powerful efforts from the likes of Shelby, the car is a unique, potent Mustang upgrade. And it now has an open-top variant.

Galpin and Fisker reworked the styling and engineering of the original Rocket, adding a body-colored carbon fiber cover that nests over the soft top and rear seats, turning the 2+2 into a two-seat roadster. The design gives the car a look quite different from the factory Mustang Convertible, and the cover can be removed when the driver wants to use the rear seats or top.

The new cover channels airflow through mesh-covered exposed carbon air outlets to effectively cut turbulence. Those outlets join aerodynamic features carried over from the coupe, including the front splitter and dual air scoops slashed into the carbon hood. There's also a set of fender outlets in front of the rear wheels blowing on the 15-in Brembo Gran Turismo brakes.

The debut Rocket Speedster wears a rich metallic red hue and rides on 21-in five-spoke alloy wheels.

The Rocket Speedster is still a concept, but Galpin does plan to sell a limited number directly to buyers and through a small network of "hand-picked dealers" around the US and the world. It has not yet announced pricing, but we do know that the Rocket coupe starts at $109,100.

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