The first-generation Saleen S351 is a modified fourth-generation Ford Mustang that features a 5.8-liter V-8 engine producing 371 horsepower and 422 foot-pounds of torque in standard trim, or up to 470 horsepower with an optional supercharger. Saleen Automotive also heavily modified or replaced other components of the standard Mustang during the conversion to an S351. These modifications included a suspension rebuild with progressive coil springs and the replacement of the standard transmission with a five-speed Tremec model.
Saleen Automotive sourced the V-8 engine used in the S351 from the Ford F150 Lightning high-performance pickup truck as a replacement for the 215-horsepower V-8 found in the fourth-generation Mustang GT used as the base of the S351. The engine was subjected to further modifications to increase power output, including the addition of enlarged Edelbrock aluminum cylinder heads and a high-performance fuel injection system capable of pumping 30 pounds of fuel per hour, and was also mated to an improved intake and exhaust system to further upgrade its capabilities. The most extensive modifications to the S351 after the engine replacement were to the Mustang's suspension; in addition to front and rear progressive coil springs, Saleen added gas front shocks and a front sway bar to improve cornering performance. The S351 also featured custom 18-inch wheels and Saleen-designed side skirts to improve aerodynamics and distinguish the car visually from stock Mustangs.