ha ha, yes another timing belt thread. Easiest way to research is to throw out a question and wait for the responses. Technology advances and things get better (usually). Are the current belts being sold for the 360 the same as in 1999, or is the construction different? If different, did the tightening specs change, i.e. freq? I recall that the 550 had a belt upgrade at some point. Did the tightening specs get revised with that belt change? It would seem that a change in construction (e.g. stiffness) would change the frequency response with tension.