Quick, the reason you couldn't find a colder plug for the LS is because there isn't one listed as a "Colder Plug for the LS" as there is for Mustangs, F-body's, ect. But, this doesn't mean there isn't a colder plug.... you just have to find it yourself. When i ran my turbo on the ls, i ran 1 range colder. Every spark plug company has its own way of oraganizing, and coding sparks plugs using a sequence of numbers and letters. I use Champion plugs, so if you look at the standard copper part number for the Champion plug for the LS It is an RC12YC or an RC12YC4. Next you have to bread down those numbers. The "R" means it is a resistor plug. The "C" is its shell style... a "C" shell type means a 5/8" hex with a 14mm thread dia. and a 3/4" reach. The 12 is your heat range number, usualy in incriments of 1. The "Y" and "C" are your electrode designs, in this case the "C" stands for copper electrode, and the "Y" is for a standard projection. The last number is a generic gap, this is done for ease of installation, so a 4 in this case means a .40 gap (the LS calls for a .44 gap).
Ok, so now take this number and move your heat range down one value and you would get an RC11YC.... now the confusing part here is that there is no 11 heat range in this series. Move one more to an RC10YC4 and you've got your plug. Now, remember that this is a standard copper plug.... so now you can cross reference it to a platinum, double platinum, ect..... A double platinum would be an RC10PYP4. I got this by changing the electrode design number to a PYP which is a double platinum.
BTW, this plug is for the 3.9. You 3.0 guys use an RS14YC6 this plug is still a 14mm thread but has a different reach with a taper and a different gap (.54 on the V6). So a step down for you guys would be an RS12YC.
