AFR=vag-com reading / 14.7, Mike..
The whole BHP calc from MAF reading can be so far out its not something I would rely on. It can also vary, some say MAF * 1.3, some say MAF * 1.2 and some say MAF * 1.25.....
You have to also take into account how boost, timing, intake temp etc etc effect how power is made, not just MAF readings...