Phormula KS-4 Knock Box
Perhaps one of the most critically important and most indispensable tools to have in a shop or on a modified car is an accurate indicator of detonation.
There are various tools on the market for monitoring detonation and then there's the Phormula KS-4. It is by far the most advanced “knock box" you'll find. It's easily configurable to suit any engine, has a digital display, memory recall, and most importantly, it has a 0-5 volt output so that you can datalog your motor's knock activity.