Where to start? Hmmm.... first is this a stock setup? Sounds like it is not if you are getting knock at 15 pounds. If you are getting knock, how much? First upgrade I would do is a hotwire and fuel pump upgrade from Caspers, Racetronixs, Fullthrottlespeed, or Ebay. Cost less than $150. Make sure it is a Walboro 340 or equivilant. Check all fuel and vacuum lines and replace (these will kill your motor). Replace your PCV valve. Check all grounds and plug wires. These things must be running perfect to run right. If the turbo is smoking, rebuild it or replace. The next upgrade should be an Alcohol injection kit. New about $500, used from $200. Best upgrade I have! You can find all kind of info at:
www.turbobuick.com and
www.turbobuicks.com and
www.gnttype.org
Welcome to the world of Turbo Buicks!