Power from the 2.0-litre turbocharged engine is unchanged, although the car features new cross-drilled brakes, lowered suspension and a Borla exhaust system with larger circular tips that replace the trapezoidal arrangement of the standard car.
The exterior is garnished in carbonfibre details, including a new roof spoiler and bonnet with functioning air vents.
A performance package with increased power is under development.
Three graphics packages are also being offered including the traditional stripes or the chequered flag and competition stickers fitted to the show car.
The Shelby Focus ST package costs $14,995, not including a donor ST. It will be limited to 500 examples a year.
Also shown by Shelby American at the Detroit show was a new wide-body version of its range-topping Shelby Mustang GT500 Super Snake.
Developing 838bhp from its 5.4-litre supercharged V8 engine, the Super Snake is now optionally available with wider wheels — 13 inches at the rear and 10 inches at the front — to improve traction.