There are so many variables it isn't funny. What oil is in the trans and diff, what diff ratio, what tyres are on the rear, different mufflers (chamber, perforated, hotdog, straight through) and then you will get variations per car from being a Friday build or mid week build. But as said above we work on a 1rwhp=1f/wkw. Lastly, Different manufacturers measure powr differently. The Japs have been knwn to do a power run with NO accesories attached to the motor (I.e alternator, aircon, power steering, sometimes water pump) where as most european manufacturers will have everything bolted on. What way Ford do it I don't know but these could cause a variation as well.