This book gives a good overview of the Sportster's history and serves as a guide for those who want to add more horsepower and torque to their Sportster's engine along with ways to improve handling to an acceptable level for high performance riding and racing. The advice on Evo engined Sporties is very comprehensive and points out the differences in building a good reliable street motor or a racing only engine. I built my 04' Sportster using this book as a guide. Making many of the modifications recommended in this book my Sportster accelerated quicker and gained several MPH on top while still having the ability to ride through town without overheating. The information on ironhead engines is not quite as good as the Evo but it still offers suggestions on how to upgrade that motor also. Sportster Performance Handbook is a good guide for the back yard mechanic it explains which modifications work best depending on how one plans to use the modified motorcycle. I highly recommend it for Evo and Ironhead enthusiasts.