[Gossypiboma]

Those numbers seem odd, thats what a stock M3 puts down. Of course dyno to dyno comparisons aren't equal, but my car with your same mods made 380whp and 275tq as do most M3's with test pipes and a tune.

If you install the headers and then happen to make 380ish whp its going to look like the headers and x-pipe alone added 40 more hp. When in fact your "baseline" numbers are off for some reason.