Can you please explain the difference between “prototyping” and “pre-production”?

Shareholder, name withheld

Although there is no formal definition or distinction, the term “prototyping” is generally associated with test castings produced early in a development program. The prototypes can be used to learn about potential casting defects (and thus modify the design), to identify material properties in various regions of the castings and, to build engines or other assembles for operational testing. Most new-design cylinder block programs will have three or four prototyping steps (design adjustments) before the final design is frozen. The prototyping period may also be referred to as the engine development or product development period.

“Pre-production” castings would refer to castings that are produced later in the program. The pre-production castings should be based on the final, frozen design (although ’last-minute’ changes can always be requested) and are generally used to build engines for bench and vehicle testing and to optimise the machining and assembly operations.

The transition from "prototyping" to "pre-production" depends as much on the timing of the design freeze as it does on the status of the overall program. In general, the term “pre-production” is used to indicate that the program is well-advanced and that the design-frozen castings are being used for validation (durability testing and extreme temperature testing), homologation (performance, emissions, oil consumption, etc) and machining/assembly optimisation. A typical new engine program may require about one or two thousand pre-production cylinder blocks over a period of approximately one or two years.