It sounds like its in the right range, if I am understanding it right.

414 - 494 = -80

-80 * 8 = 640, or .640 g's

~60 * (640/10) = ~ -3840 or negative 38.4 degrees

The ABS (absolutes) are used to keep the math working, while the check on xGForce.bit15 is used to detect if it is a negative number. I don't think you are overflowing with your * 20, but a quick check of the xRaw might be in order.