You don't even know what global illumination is, do you?
In practice, however, only the simulation of diffuse inter-reflection or caustics is called global illumination.
It's basically a better (much more taxing) version of ambient occlusion.
Forza has a real time lighting engine that is applied to moving objects (mostly cars). This is a static system but calculated in real time. A dynamic engine does the same thing but allows the lightsource to move. As for environments, Forza does in fact use a pre baked system where they take a real time lighting engine and essentially save the shadows created and than apply them to the track texturing. An unfortunate side effect from T10s graphics engine (which was last properly rebuilt during FM3 afaik) is the top down environment shadow mapping to cars.
Forza 5 does in fact use some sort of AO or even GI for the cars (which is entirely possible thanks to the track and car lighting engines being completely seperate coupled with "image based lighting" to make the cars somewhat lit by the environment. Add in the fact that the cars do have a real time lighting engine applied to them the shadows they create are entirely dynamic. If they weren't, the shadows moving in the interior camera simply would not exist.
Reflections
in the real world are indeed a product of light. Reflections in a
game engine are not unless you're using raytracing which neither DC or FM5 do. If they did, you would see the cars reflecting themselves (i.e mirrors and wings) and other cars in all conditions (i.e interior cameras, exterior cameras) which doesn't happen. Both games would likely use a form of cube mapping to do their reflections. Cube mapping is almost as good as raytracing mind you.
The windscreen reflections would use the same reflections seen in bonnet cams where you can see other dynamic objects in real time. They are both essentially taking a picture of the dash and pasting it on the windscreen taking into account rake and curvature of the windscreen. This is why you can clearly see the shadows being cast over the dashboard being reflected in the windscreen in both games. FM5 however has the drivers hands and steering wheel reflected in real time. The reflection model will also only allow a set amount of light reflect (same as the paint reflections are set to allow a certain amount of colour and reflection through) which is why the dash reflections become less and less apparent when there is less light hitting the dashboard.
So, in closing. Both games are doing virtually the same thing in regards to windscreen reflections with Forza doing a tiny little bit more reflections included but it doesn't appear to be as sharp as it is in DC. Will have to wait for some better direct feed videos from both games.
