Gearbox/ final drive
Story behind the idea - BMW (<3) had only 3 manual gearboxes on the E36, Getrag that would fit any petrol engine and 2 ZF units that would go diesel and petrol respectively.. and 3 final drive housing sizes, small for anything up to 2.0 i6, medium for 2.5-2.8 i6 and diesels, and a large one for M3 only
My idea - Gear spacing, if left unchanged between the trims and engines would count as a mass produced gearbox for the current model or even multiple models that use the same gearbox, same goes for top speed (could be named final drive for the purpose of the post) and all that would count toward -% for the production cost, as the parts are interchangeable