why do headers / ypipe require a tune?
Any time you change the way the air enters the MAF like with an intake you should adjust for it. Headers don't just lower back pressure like with a catback, they scavenge the cylinders for more filling which will throw your tune off drastically.
the degradation of O2 sensor performance (if not simple
deletion). The VE will change some, but at the big end it's
largely ignored. Mistrimming from poor sensor performance,
though, will dog you all over the map (idle problems stick
around into WOT, etc.) and you would like to make the "non-
performance related" tweaks you can, to keep from hurting
performance via the back door.


