A few extras. The first three runs ..... ( stock....Muffler......then headers, and muffler)..... dont tell the whole story. Those were done at WOT, and the stock map does use the o2 sensor there, but as we puddled around on the dyno, at 1/4 to 1/2 throttle... we saw way high a/f ratioes approaching 20, which is way to lean. As the stock map only "widebands" from closed to 1/8 throttle, and wot..... everything between is from the preloaded map, which is lean to start with....and leaner with pipe.....and waaaay leaner with headers, and pipe. Personally I would not run headers,and open pipe with stock map.....simply to dangerously lean...imho. You cannot hear, or see this, but the dyno reveals this.... To much horror.