@gundy @The Aero Man
Basically.... the board / tech guys at the time looked at a bunch of swapped cars... they put the VPI of those cars, the weight, and the HP of the new engines into a spreadsheet. Then, they squinted and said something like ... "well.... I think this combo should get around XXX points, and this other combo is about on par with this other car which is YYY points, and this third combo should be about ZZZ points" and they put these values into the spreadsheet as well.
So then they said, "Ok, now we need to make a mathematical formula, which takes as inputs the VPI, weight, and new HP, and outputs as close to XXX, YYY, and ZZZ as possible."
So they did some curve data fitting and playing around in excel, and eventually they came up with the formula that you see there. That's where the 6th power comes from.. and the coefficient.
The 16 comes in to play because a second goal of the swap formula was the idea that any car, no matter how low the HP was from the factory, should be able to swap to a decent PWR for just 50 points. As it currently stands, going to 16:1 PWR is 50 points, and anything more powerful than that will be more than 50 points. But, because the online calculator truncates the decimal place instead of rounding, you can go all the way to 14.23 : 1 before taking more than 50 points for an engine swap (50.984 points => 50 points). The PWR is calculated by the new HP and a special weight that they have listed for each car in a database.
Concerning your question of "Why does it ask for original HP it makes no difference in the VPI see below", Mike Chisek will answer that question for you. His email is firstname.lastname@example.org and his phone number is 704-241-8215. You will also notice that the formula as written in the rulebook is incorrect. You should ask him about this as well.