I think a good point has been made here, in that the cetane value of the fuel is a major factor in what timing works best. All the numbers that get kicked around are in pulse method discussions, because that IS the way that works best. However, if you go back to the original 6.9 specs, the method used at that time was luminosity, and luminosity required that you know your cetane value, and you referred to a chart to time ACCORDING to the cetane value. Ideally, we would have a cetane value timing chart for the pulse method, but we don't. This thread appears to be addressing that, but there is not enough science behind it for anything to be conclusive. SO, the factory spec is 8.5 degrees PLUS or MINUS 2 degrees. That means that by the "law" anybody running 6.5 degrees to 10.5 degrees is not wrong. However, all of us that time know how much of a difference 2 degrees can make, so we always tend to time according to what our experience shows the local fuel requires. Unfortunately, for those who travel a long distance to get timing done, unless you have enough fuel that you are running your home fuel when you get timed, there is no guarantee that your performance will be equal once you get back to where you normally buy fuel.