They are both excellent books by the same author, on very similar subjects, so of course a lot of the content will be identical. If you had to write a chapter on intercooling a supercharged engine, and intercooling a turbocharged engine, what would be different?
I have both books, and would recommend them both, but a lot of the content is very similar if not identical in both books.
A lot of the basics on subjects such as selecting a compression ratio, engine building, fuels, manifold design, intercooling, detonation, instrumentation, testing, and so on are really the same in both books.
And it does contain a lot of personal opinion, but then the guy has the knowledge and experience, and I am all the wiser from hearing corky's views.
The big difference between these two books and others is that the information is recent. There are plenty of other really dated 1970's hot rodding books on how to fit a 6-71 GM blower onto your small block Chev. But these books discuss far more modern hardware available today.