Depending on the exhaust/mufflers, that may not hurt it much. My car runs almost the exact same number with or without my 3" exhaust. My exhaust exits before the rear tire with Dynomax race bullets for mufflers if that helps.
I run little bit more of a muffler. Dynomax Ultra Flo offset 3" that dumps in front of the rear housing. Also have a Pypes 3" X pipe. I have never made a run with open headers so I dont know if there is a difference or not.
Hopefully will find out soon what it will run.