Well just managed to import the Porsche 914 to Trackmania. It was modeled with Maya, however had to be exported to 3ds Max, where it was cleaned up and then exported to a .3ds file.
Finally it could be converted into the Trackmania .gbx file. The textures were exported as .dds files
some in game shots. Still need to adjust the alpha channels, so its not too shiny :D
The car painter in the game:
driving the car :)