Perhaps the last great engineering feat of Smokey Yunick’s life was the creation and operation of his famed “hot vapor” or Adiabatic engine. Many of you remember reading stories of it in Hot Rod Magazine, Car and Driver, and other books back in the day. The premise of it and every other adiabatic engine is to retain as much heat as possible, raising the efficiency of combustion and operation rather than sending the heat down the exhaust pipe and out the back of the car or truck. Smokey did not invent these principles and adiabatic engines had been around for decades before he built his but who knew that the Army was also in on the fun?
In the 1970s the US Army got with Cummins to develop engines that were specialized and in many ways advanced for their time. Engines that did not use liquid lubricants and adiabatic engines were two of the main focus areas. The project got very far along and actually resulted in the testing of adiabatic power plants in trucks and tanks.
The results? Not shockingly, they were really good. So what happened and why? Hemmings recently did an awesome story on the engines, the project, the desires, and the outcome of the tests that happened a couple of decades ago. A fascinating read.