I have read about the uncorking/desmogging process mods people are doing for some time on TT now. There is one thing most, if not all, are leaving out. There is another smog device that seems to be eluding everyone. Quite frankly, I am surprised no one on TT has even written about it, because, IMO this elusive smog device is still in fact leaving our beloved XRL's and XRR's partially smogged and corked, not in a minor way either. Better yet, this smog device is probably the simplest to understand and simplest to remove and replace(however, probably the most costly). "What is this elusive smog device?" I am sure some of you might be asking yourselves while reading this. This elusive smog device is nothing more than the stock exhaust system, more specifically the headers. Here's why. When I was in the process of building my own headers I became more familiar with how the stock headers were made and began to realize how restrictive they really are. (My theory of why the stock headers are a smog device is below) The first thing that caught my eye when I took the stock headers off for the first time was the size of the Exhaust port outlet and the inside diameter of the header tubes. The Exhaust port outlet diameter is almost exactly 1 inch (I mic'd it). The header tube(s) inlet size is just about 1 inch also. The Header tubes start out being about 1 inch tubing at the factory. They expand the beginning of the header tubes to about 1.125(1 1/8) inches to join up with the mounting flange. Inside the header tubes is a big glob of weld joining the flange and the header tube. That in itself is restrictive enough. Another thing I noticed was the small radii of the bends of the tubing. The smaller the radii the more restrictive they will be. The big "U" bend on the Left Exhaust port header tube is yet another restrictive feature of these stock headers. If you consider everything in the above paragraph you will come to realize that the stock headers are indeed very restrictive. Now to the part as to why I think the stock headers are a smog device. You take that restricted air flow in the headers and what do you get? Exhaust Gas Recirculation. Simply put, the headers are alowing more exhaust gases to recirculate back into the combustion chamber(more back pressure equals more EGR) to mix with the fresh fuel mixture to be re-burned and that equates to quite a bit of power loss. If you have gone through all the trouble of uncorking, carb mods and desmogging your XR and still don't think the performance gains are all that impressive, try removing the stock headers and replacing them with some high flowing exhaust headers. I did and I unleashed even more performance than I expected along with all of the other mods.