We make a closed-loop knock controller system, called the J&S SafeGuard.
Using a single knock sensor, the unit retards only the cylinders that are pinging. Our newest units incorporate boost retard, with "when" and "how much" knobs.
Here's a link to an article written by Larry Henderson from a few years ago. The photos in the article are of our earlier "ugly duckling" version.
http://www.mustangworks.com/articles...ckControl.html
