Curling is due to the upper layers cooling more than the lower layers, pulling inward and then lifting up from the bed. To reduce this you must reduce the differential temps between the top and bottom layers. You can set your bed to be hotter for the first layer, then somewhat cooler after the first couple of layers. Contrary to previous poster, you want to reduce your usage of fans, perhaps turn them on only for overhangs. Finally, if you can enclose the print area that's best of all - not sure how easy that is to do with your machine. As a partial alternative, you can create a heat barrier around the outside of your part using the skirt setting in S3D - make the number of layers the full height of your part - a lot of plastic I know but it will keep the bed heat in the higher layers of the part. Per previous posts, a brim helps a lot as well, but I'm not sure if S3D allows separate control over skirt and brim. To build the barrier requires skirt, but you obviously don't want a full height brim. If someone knows how to do this, maybe they'll chime in. Meanwhile, a work around would be to just design the heat barrier in your modeler and print it along with your objects. To further refine this, if your part is not too big, you can experiment with making the modeled barrier be wider at the bottom, to grab more heat coming from the bed, then narrower as you get higher on your print, to "trap" it in - the heat will convect upwards but will get closer to your model as it goes past. Good luck! Really big parts can be tough even using PLA (nevermind ABS or PC!), and it's why professional machines have enclosed chambers.