I have 800cc Saline implants, over filled. Can these be filled to 1800 or do I need to order custom implants?

I personally refrain from making value judgements or statements about cosmetic surgery. However, in this instance- I would assert that implants of this size are absurd and have no significant value to quality of life. However, I'm sure you will find someone out there to accommodate you.

Bravo, Tom.  I couldn't have said it better.  I am sure you will find some one, notice I didn't say board certified plastic surgeon, who will accommodate your request.  You are only asking for future long term problems by doing this.  I know of no American companies that will make custom implants at this point but there are some in South and Central America.  Good luck.

Saline implants can be overfilled but there is a limit.  If you want implants over filled by that much they would need to be custom ordered. Keep in mind that the manufacturing company's do not cover overfilling with their warranties.  Also, the bigger the implant the bigger the chance of complications. 

There afre several ways to get the fake look-either with overfilled saline implants, custom XL silicone implants or XL tissue custom expanders.It depends really on what cc size to want to get.
You can think of a saline implant as a balloon. The manufacturer recommends an overfill of about 20cc but they have been shown to be able to be filled much more than that. They do start loosing their shape and can significantly distort the appearance of your breasts. 
 I do overfill espcially since the FDA has restricted saline and silicone implants to a maximum saline shell size of 800cc and maximum silicone size of 800cc. I do not know why that number was picked arbitrarily. 
So, I do do breast reconstructions greater than that with XL tissue expanders which do pride a greater diameter and projection and upper pole fullness and allow the size to be adjusted either up or down. Also, the shell of the saline implants are very thin and can dreflate more easily. You may want to visit my site below which explains everything, esp for XL sizes which is my specialty, either initially or revisional surgery.