Just took it out for the first time tonight after installing the headers. Not really sure about bottom end, mabe a little better but definitely noticed a difference in upper range. Much smoother powerband. No more flattening out around 4000rpm. Little more driving it around and I'll post again. And yes they do bolt to factory pipes. I also don't think I am getting the full effect of them considering I only have a cat back system and still have factory y which I would assume is my most restrictive part in my exhaust now.