A methodology for rapid development of purpose-built, heavy-fueled engines is being created. The methodology leverages best-in-class computational tools, component supplier expertise, user-programmable ECUs, and rapid prototyping to quickly provide custom engines for demanding military applications. . First-tier automotive suppliers are being used extensively on non-complex standard components to reduce the development time. Our design methodology aggressively eliminates unnecessary components and incorporates various other weight-saving features to minimize system weight. The anticipated total development time to a working prototype is less than 15 months for this first iteration of the methodology, and will be further reduced for any subsequent design iterations.