GM's "Top End Cleaner" - knock reducer in a can.

Basic principle is that the PCV system spits oil back into the intake, carbon gets built up on the heads/valves, and result in detonation causing, raised hot spots.
This stuff is pretty simple, suck it in while the engine is running, let it sit in the combustion chamber for some time, then burn it all off.

There are 2 versions of the Cleaner, spray, and liquid in a can. I've used the spray can, and many others have used the liquid version.

Spray:

The can leads you to believe its for carb engines leaving you somewhat clueless on where to spray it. My solution was to remove the upper Ic, and spray the cleaner directly into the throttle body. You can just leave the outlet of your turbo open for this, just be careful not to drop anything in there. With the engine running, and your hand on the throttle lever, start spraying into the intake. The cleaner will cause harsh idle, and you may wish to give it a little throttle by rotating the throttle lever slightly as it tries to die (also helps suck in more cleaner). Continue feeding the truck the entire can. When your almost out, go ahead and try to stall it out, if you don't succeed then just shut off the truck. You want it to sit and allow chemical reactions to clean up your cylinders for a good amount of time, the can says 10-20 minutes, you can wait longer. You'll probably notice it smoked alot during the process, and is probably still smoking while you wait for the scrubbing bubbles to do their work. Wait till you start it up again. The resulting plume of smoke should make for a good impression on the ricers next door. Changing the oil is a definite next step. Im not sure about the cleaners effect on the spark plugs, but you may consider doing a fresh ignition at this point. After the smoke clears, you should feel strong and ready to burn off some boost.</p>

Liquid:

It is available at most GM dealerships. I called a local GM dealer it was $6.18 a can. Part # 1050002. It will take roughly 2.5 hours to do. You will need a short piece of silicone vacuum line (the smallest internal diameter) 4mm sound right? Then take the red *straw* off of a can of WD40. Use a 3" piece of that straw and shove it in the end of the vacuum hose. Make sure it is in real tight. Push it in the vacuum hose until about a 1/2" is sticking out. This is what you will use to draw the Top engine cleaner out of the can. With the engine running, remove the brake booster vacuum line. Once you take that plastic piece off, put a funnel in the end of it. Its best you figure out what funnel will fit that before you start all this. Put the end of the funnel on the hose, and then put the end of the silicone hose without the straw tip in the funnel. You will want to have opened the can of top engine cleaner to puncture the metal cap so when you are ready to begin, it is just a matter of unscrewing the cap. The idea here is to draw very slowly, with the plastic straw end. It will make the engine stall if you just submerge it, so just hold the end of the hose so it sucks small amounts of cleaner out. You will see what I mean about going slowly. Once you get down to about 1/3 of a can left take the hose setup and set it aside. Holding the funnel in one hand take the remaining top engine cleaner and dump it in the funnel. You will want to stall the engine out. So dump it fast. Then you can hook up the brake booster, and get it put back together. Let it sit for about 2 hours. Then start it up. It will be difficult to start. Then once it starts up, you will see lots of white smoke pour out the exhaust. So you may want to think of a place to do this, that you won't disturb any neighbors . It is a lot of smoke, you'll laugh once you do this. Get on the throttle a couple times and rev it to get the cleaner to burn out. The smoke should go away in about 5-10 minutes. That is about it. It is important that you do an oil change immediately. I usually don't drive much more than 10 miles after I do the top engine cleaner, before I do an oil change.
This portion was taken from the UBB.. referencing "kwick6" or Scott... (slightly edited for your pleasure) </p>