Well, are you talking about the Chibis that project from their henshin devices? Or the small Toy-sized versions that grow?

Well, the chibis are an easier way to communicate with them. The Engines can only stay in their giant size for a short amount of time due to them being from the Machine World.

i get the whole engine cast thing. but the projections from the changers, it doesnt make any sense

Again, just an easier way for them to communicate lol.

Well, the changer projections are usually known as the "Soul Form" of the engines, so you could say it's their deluded self image. :P

ok, i dont understand how the engines hate the gaiark, their entire world is enhabited by cars, how much more could the gaiark do to the world