625hp 1970 Boss Mustang Fastback

My name is Chris Ashton. I started building the 1970 Ruffian Mustang fastback in 2016 and I finished two days before SEMA 2019. This was my first ground-up build and it was designed to kick butt at the autocross as well as get me to work on Fridays.

The build is heavily inspired by the muscle cars in the Trans-American race series of the late 60s and 70s.

A lot of the modifications performed on this car are the same as the original race cars, although I used newer technologies when I had the opportunity to do so without affecting the vintage look and feel. I also added creature comforts to make the car more drivable on the street. It has power steering, power brakes, AC, Heat, and electronically adjustable coilover suspension.

I am responsible for the whole build, including the visual design, research, installation, fabrication and sheet metal work. The body is all steel, done on a cheap planishing hammer and English wheel. In total, I have over 1700 hours of labor into it, which isn’t bad considering the car’s presence.

The engine is a carbureted, seven-liter, aluminum block stroker LS3 making 625hp. The motor was mounted 2.5” rearward and 1” lower than the factory setup to improve weight distribution. It drives a six-speed super magnum t-56 transmission and a Ford 9” floating rear axle with a watts link setup and 4.11:1 gears.

3D-printed nylon parts are used throughout the car, such as the vent inserts, 427 badging, and window rollers. The bumpers have been fitted and re-chromed, and the front fenders are pitched down an inch for good looks and improved aero (just like the race cars). Most of the chrome trim has been removed and flush mount glass was used to give the car a sleek look.

The car wears custom Signature ONE wheels – 19×12.5” in the rear and 18×11” in the front. Wide Toyo Proxes R888R’s are used at all four corners. 345’s attempt to put the power down while 315’s handle directional changes.

The car is finished in a 1978 Porsche Olive Green paint. The Boss side stripes are reflective black 3M vinyl (a nod to the original Boss 302 cars) and the black hood is actually exposed carbon fiber on an Anvil Auto hood. Knife maker, Jake Palm hand-built the pistol grip shifter and South County Auto Body handled paintwork.

 …it was designed to kick butt at the autocross as well as get me to work on Fridays.

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