I believe that even though AMS2 share the engine with other game, Reiza has rewritten a big part of the code both for physic and for FFB. Can this be confirmed by Reiza team members. AMS2 does not feel like other games sharing the same engine, the driving is different. I believe it would help AMS2 get a better acceptance if that aspect of the physic was clarified.
Renato has commented on this topic at RD AMS2 Beta Now Live | Development Roadmap Automobilista 2: New Preview Video Released the madness physics engine is a great physics engine. As Renato said "making clear we chose this engine also because of the physics and not in spite of it."
Yes and no... There's a video where the guy changes parameters for some cubes and shows how the same engine can make different friction behaviours for the same object.... I should have saved that link, think it very useful as example for these moments. Someone have the link for this video? Edit: Short answer, you have nothing to wory about AMS2 + Madnes Engine. Almost everything can be changed by parameters and Reiza have full access to the sourcode to change in the core whatever they need .
I think its a complicated question to answer. Because eventhough the behaviour of the cars can be altered to some degree by inputting other parameters into the (Madness) physics engine than was inputted in pCars2 - then there is some basic boundaries for such an engine that cannot be altered without changing the whole engine. As an example you cannot get iRacings cars to behave as rF2 cars in certain (urgent) situations because iRacings physics engine and TM are not equal to rF2´s ditto.
I think that using the same engine doesn't mean that the physics will be the same, an engine can really be modified to create different results; just looking at games running on Unreal Engine 4 can be a good example.