Air Cool VW (Beetle)
How to Hot Rod Volkswagen Engines by Bill Fisher
This books is wonderful. It has actual dyno testing for most of the recommended tunings. The only down side is that some of the material is pretty dated, and they talk about equipment that I've never seen for sale. Great, in depth info and solid explanations.
The best part of this book are the dyno charts comparing horsepower gains. There are charts comparing ignition, single barrel carburetors, two barrel carburetors, dual carburetors, exhaust systems, head flow tests. There are chapters on history, bolt on mods, price of horsepower, horsepower ratings, ignition, carburetors, exhaust, cylinder heads, pistons and cylinders, cranks, lubrication and cooling, cam and valves, blueprinting, assembly tips, superchargers, Porsche engines, swapping a late model engine into a pre-66 car, converting flat engines to upright, suspension and handling, some parts info.
Some of the info is dated, but I learned a ton from this book. This will open your eyes to some of the crazy claims that people make for various mods and "bolt on horsepower". This book is very useful to someone like me who just wants better performance, or to someone building an all out VW monster.