I was about to buy one of those Pulstar sparkplugs for my 2001 TT online when I was asked to select between these two engine types.  What do the "C" and the "X" stand for?  I pretty sure that 1.8/L4 denotes a 1.8 liter inline 4 cylinder engine, I'm guessing AWP has something to do with all-wheel drive or all-wheel power, and FI stands for Fuel Injection, but I couldn't make heads or tails of C and X.

Also, has anyone tried a Pulstar sparkplug?  I saw an add in a magazine and figured I'd give it a shot.

Thanks.

They're a money-wasting gimmick. Stay with the stock plugs. With hundreds to choose from, and millions to spend on research, the manufacturer has selected the plug which your engine is happiest with. Do not stray.

If there was a tenth of a mile per gallon to gain from a miracle spark plug, the manufacturers would be on them in such quantities that they'd no longer cost twelve bucks each. They want the best mileage possible, just like we do- theirs is to pass CAFE standards.