Drivetrain loss is a %, because as someone mentioned, it is created by trying to overcome moving parts which as you turn and move them faster continue to take a proportionate amount of power. Its not a precise science, but generally speaking most rear wheel drive cars see about 15% drivetrain loss for a manual transmission, and close to 20% for an automatic. These numbers are generally higher for front wheel drive cars, 17.5% - 18% is generally used for the contour. Also if you add heavy components in your drivetrain, or taller gearing, this also constributes to drivetrain loss.
Originally posted by MapOfTaziFoSho:
If we assume 18% loss...I multiply the 401 by 118% or 1.18 to get 473.18 crank hp. The only real way to find out I suppose would be to throw it on an engine dyno, but I don't really think Sun cares that much... 
Jim who's math is correct? 
The correct math is to divide, 118% is an increased of 18% vs. dividing which gets you the number it would take to have an 18% loss. So 401/(1-.18) is correct. 
