Tom wrote that article and did a fine job. He also consulted me, and if I recal, I may have been the one who sourced the factory data that I had available. The published numbers are someone subjective, as many of you have observed. Different engines had different horsepower ratings depending on where their target marketing area was, and the elevations associated with them. Factory horsepower ranges went from around 155 to 175 for the 6.9. There was a similar range for the 7.3 All those numbers represented different IP calibrations, which is why there are so many part numbers for the 6.9/7.3 injection pumps. There are really only 4 physically different pumps, but there is something like 16 part numbers for those same 4 pumps, each representing a different calibration. I like the idea behind that web site forgotten diesels, but I'd say their info is very course. For instance, they list the applications as F250/F350, but seem to have forgotten that Ford made E series IDI vans.