This highly practical and useful book covers brilliant techniques that take the guesswork out of performance modification. Using just some low-cost tools, you can easily measure the flow restriction of your car's intake and exhaust. It's like having a huge flow-bench always available. By making some simple on-road measurements, you can plot the shape of the engine's power and torque curves - no dyno needed. This allows you to not only see if performance modifications to the engine are improving power, but also see where in the rev range those changes are occurring. Assess the worth of cams, a larger turbo, changed boost control or altered engine management mapping. But the book doesn't stop there - it also shows you how to measure your car's aerodynamics, seeing if at speed your car is developing lift or downforce. Want to make a rear wing work well? Test the angle at which downforce is greatest. You can also test the aerodynamic airflow through oil coolers, intercoolers and radiators. Interested in improving your suspension? By using a low-cost app and a smartphone, you can accurately measure suspension behaviour. If you want a practical, hands-on book that will immediately save you money, show where modifications are most needed, and can be used to assess performance outcomes, this is the book for you. The author is an enthusiastic hands-on modifier who performs all work on his cars himself in his home workshop. He has been testing car modifications on his own road cars for more than 25 years.