In response to the tube in tube, merged headers question. The tube in tube is just as it says the collector slides into the exhaust. Merged headers have ( or at least the cat headers) A flange. What merged means is that where all the tubes instead of 4 straight cut tubes ending in the collector, the 4 tubes are scalloped to a point inside the collector. This is to help the exhaust gases flow into the collector smoother. The cost to order the cat headers with the merged tubes was about $100 more 6yrs ago. When I got mine I had to sand the insides where the tubes merge because of the crapy weld job . loganjr