Is it possible to create a bootcamp image without compression?
Not currently. Why are you looking to turn off compression?
Sometimes when I have very big boot camp partition, I would also want to disable the compression…as it take way too much time to create the image. Other than zero compression, would setting minimum compression helps?
Compressions is not usually the think that takes a long time (seek time and file access are the biggest factors). I have never seen CPU got to 100%. I would recommend using block-based. It is much faster on spinning platter (non SSD) drives.