They must be using a correction factor for naturally aspirated engines ,I am not sure but I belive it is differrent for turbo because at sea level or 29. 92 ' of mercury and 60 f we all are at 14. 7 psi or 1 bar. As you go up you loose a couple of p. s. i. for every 1000 feet or so. Hence the turbo you just add them write back. I read about this a while ago and will look up the exact numbers. But basically if you go up 5000 feet in elevation and loose 5 psi of atmosphere,all you have to do is add 5 psi boost and you are back to the same h. p. So in theory if our trucks were the same and I was at sea level running 50 psi and you were at 5000' and running 55 psi we would be making the same power and doing the same 1/4 mile etc...