This is going to be a short 'guide'.

The reason I'm making it is because designing cars without limitations is just boring. At the same time any challenges and competitions out there are pretty arbitrary, so I decided to go with official regulations that exist to balance the performance of the cars taking part in the races.

I compiled a list of various racing series regulations (far from complete, but I will be updating it). These come from open sources available to me, previous Automation challenges and a bit of my arbitrary judgement:

https://docs.google.com/spreadsheets/d/1dJ3z8LlJ8S4FzZZdRM8vkzXln1GL3wOC/edit?usp=sharing&ouid=106264211467113902559&rtpof=true&sd=true

Please feel free to use these in your creations, challenges and for whatever other reasons.
Any feedback on accuracy and improvement is also welcome.

Update 1.1: added Group R-GT and Group B Rally classes - both have very few limitations compared to others and allow for some crazy builds.
Update 1.2: added SCORE regulations for Baja cars and trucks. Though the official regulations don't put a limit on type of fuel, I still did so that engine size limitations make actual sense.
Update 1.3: Group A Rally and WRC now have restrictions on Intake air flow (basically size), not turbine inducer size; Group A Touring has increased max cost and max quality restrictions - same as in GT3 to allow for better replicas of original Group A cars.