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The Consolidated XPT-4 was a version of the PT-3 that used an experimental Fairchild-Caminez engine in place of the 220hp Wright J-5 (R-790) Whirlwind nine-cylinder air-cooled radial engine.
The sole XPT-4 (PT-3 28-293/ P-528) was given a 125hp Fairchild-Caminez 447 C engine. This was an air-cooled four cylinder four stroke radial engine designed by Harold Caminez and developed by the Fairchild-Caminez Engine Corporation. Each cylinder pushed a roller onto a double-lobed cam mounted on the output shaft, allowing two pistons to push at the same time, doubling the number of power strokes on each revolution of the output shaft. This eliminated the need for a crank shaft. The 447C operated at lower speed than the Whirlwind - 960rpm compared to 2,000rpm and was also significantly smaller (86.4cm by 86.4 cm by 68.6cm compared to 112.4cm by 149.9cm by 132.1cm) and lighter (360lb compared to 508lb), and plans were in place to scale it up to increase its power output.
The Fairchild-Caminez engine received a type certificate in 1928 but soon afterwards all development work was cancelled, probably because it failed its Navy trials due to excessive vibration. For the engine to move smoothly it would have had to have been built to very high levels of accuracy to make sure that each pair of opposing pistons were synchronised. It isn't clear if the PT-4 was actually built, but PT-3 28-293/ P-528 was allocated to the project.