n2ojunkie

OK this may sound like a stupid question but I plan on building a engine this summer or next winter and need to work out some issues. First its going to be a 402/408 some where in that range anyways. If I tune it for open headers thru elect, cutouts, how would running the stock exhaust affect the car? Would I need two tunes? or would it just run rich or lean? I would only put about 50-60 miles a week (nice days) with the exhaust closed.

Or would it be better to tune for the closed exhaust and have the pcm try and compensate for the difference?

Just some questions going thru my head at work.