Help, how do I set burning to 2x (it burns faster no matter what I set)

[AGJ]

These are what I use for all my DVD back ups

DVD+R 8X TAIYO YUDEN SILVER LACQUER (100 PCS)

I burn them at 8x speed, booktype to DVD-ROM and use ImgBurn as the burn engine. I have not gotten a coaster in over 2 years of using these and they still playback like it was the first day I burned/watched them