ABS / HIPS Melting on large print, suggested settings?

On large prints my parts start to melt and sag when using ABS with HIPS support. I’m running a TAZ 6 with ABS and HIPS at 240C and 110C Bed. Using S3d. The first few hours look great but after it gets enough insulation that the heat build and the part starts to sag/warp/melt. The HIPS turns brown. I don’t have an enclosure yet ( should be here at week’s end) but I’m printing with a ooze shield which provides a similar effect. I want to drop the bed temp after a couple layers but I don’t want the ABS to warp and delaminate. Does anyone have a proven solution?

I have done 24h prints with HIPS at 240 in an enclosure and it has never perceptibly changed color. If the plastic has time to change color during the time it passes through the nozzle, I’d suspect your nozzle is too hot. Also, my hips prints require substantial fan (~50%) to not sag and look melty. (I don’t do ABS so no idea there.)