This article is from the VW Performance FAQ, by with numerous contributions by Jan Vandenbrande others.
A:A nice contribution by Bob April [Edited]:
The following books have been worthwhile to me. In general,
they are like a college education; after you have read them
you will be better positioned to make specific decisions.
"Volkswagen Water-Cooled, Front-Drive Performance Book" Greg
Raven, Available from US mailorder houses. Probably the most
relevant book for Water Cooled VWs. Note that Greg is on the
net at firstname.lastname@example.org
"How to Make Your Car Handle", Fred Puhn. Explains the
basics of car dynamics, why you would want to make certain
modifications, and how to do some of them. [Ed: This book is
pretty old by now and except for the "theoretical" issues,
which are very good, may be a bit outdated. There is however
another book available by the same name but different author
that is more up to date. I have seen copies at better
bookstores and Auto parts "supermarkets"].
"Performance Handling, How to Make Your Car Handle,
Techniques for the 1990s", Don Alexander, Motor Books
International, Osceola, Wisconsion, 1991, ISBN # 0-87938-418-
2. This book seems to be a modern day version of the Fred
Puhn's book though it lacks some of the "do-it-yourself"
procedures (e.g., how to adjust toe, how to make the tool).
"Prepare to Win", "Tune to Win", Carroll Smith. After
reading "Prepare to Win" you will know how to modify your
chassis safely, i.e. why banging bolts in place with a
hammer is bad, and what to do instead. You will also learn
to recognize quality performance parts as compared to cheap
junk. "Tune to Win" is the postgraduate follow up to the
Puhn book. I never would have considered accelerating a
rear wheel drive car to get out of an oversteer situation.
Learn why a Formula V race car has a rear roll bar where
your car has an _anti_roll bar.
"Racing Engine Preparation", Waddell Wilson and Steve Smith.
Old, and discusses V-8s, but there's a lot of stuff you can
use. Waddell's engines have been around Daytona many
thousands of times.
"Bosch Fuel Injection & Engine Management", Charles Probst.
Incredibly clear descriptions of the systems, way too
conservative in describing and valuing modifications.
"Brake Handbook", Fred Puhn. If you're going to do more
than change fluid and pads.
"Clutch and Flywheel Handbook", Tom Monroe. In conjunction
with the shop manual, explained why it was a really bad idea
to speed shift my X1/9 at autocrosses.
"Secrets of Autocrossing", Watts.
"The Front-Wheel Drive High-Performance Advantage", by Jack
Doo, ISBN # 0-87938-298-8, Motorbooks International,