hi every one…i have some model for my new work and as the models are very high poly meshes(154 milion polygons for example) I need bigger texture size than 8192 for export because when i render,it loses some good details i have…if there is any way i can get better results i will be thankfull…i really need this,please help me 
Break your model into SubTools, UV map them and export multiple textures.
Even 8K maps are rarely used professionally. They are huge files, and the rendering engine has no choice but to load the entire texture – even if your camera is zoomed in on a small section of the surface. This makes them very inefficient. Odds are good that those details you’re losing are not apparent at all when you’re viewing the entire model, which means that a lower resolution is fine at that distance. As you come closer to the surface, that’s when you would switch to the more detailed texture. But even if you do need the highest resolution for the entire model at once, you’ll still be more efficient using multiple textures than one. This is partly because your rendering engine can offload some of that data when your view changes and those surfaces go out of sight. But it’s also because the larger the chunk of memory an asset needs, the less flexibility your computer has in how to work with that asset. The computer MUST find one big, contiguous chunk of memory and then has to work around that. But with multiple smaller files – even if they add up to the same amount – your computer can stick them in different places in its memory, giving it more flexibility to work with your image as a whole.