The Jennings book is a simple masterpiece. He has taken some research that was done and published by Nagao, all to do with inlet tract delivery ratios, and without emphasising it he introduced the idea of port time areas. I am not sure if Nagao really understood the value of that idea, and it was a gem. Jennings read it and understood the value. He did his own investigation, and turned a minor suggestion into a real tool. This book is about the single idea of how to use port time-area diagrams. The other material in the book is good filler, but without port time-area diagrams I doubt the Jennings would ever have written this book. Written in 1973, and way ahead of its time, this is a must have book. This book really puts some method in to your tuning madness, just wonderful. Get it if you can!