Much of engineering is based on emperically derived formulas and tables that have known relationships. It relates to science but is not the same describing relationships strictly on physics and chemistry. This is the way stuff gets done. This why Pipemax provides good guidance at the same times Burns and Elston can provide equally good guidance even though in some instances it is rather different guidelines. All of its emperically derived - although some of you are well aware DMtovof and others on ST have had deep discussions and attempted various models of the gas and sound waves.
How about dynomax? Does anyone think Larry Atherthon is a physicist or hired a team of them to develop the F&E and Wave modeling?
I can tell you the company I worked for sold a critical safety item to two of the three big US car companies that was emperically derived, developed, and tested. There were a few physisists working on computer models but that was for down the road when it was thought that solid state equivalents could be made cheaper and smaller.