The reference material behind the calculators - chassis codes, engine families, and generation breakdowns, written by people who work on these cars.
Search any parts catalog, tuning forum, or classified listing and you'll hit chassis and engine codes before you hit model names - "FBO N54," "F80 ZCP," "987.2 Cayman S." These guides decode the shorthand, and every code links back to the tools: identify your exact car with the VIN Decoder, then run your numbers through the calculators.