there are a lot of numbers to crunch right there, and obviously automobile exhaust is not ideal (friction, etc), I was just confirming what others said. I guess I would look at what aftermarket companies have on their specs, because they are the ones who run the tests and hopefully design for optimum hp/torque gains and not just being loud. I'm sure mimicking there pipe diameter and choosing a smooth shape for your piping will yield you good results. Like I said, just cuz I know a few equations doesnt mean I know the best thing for your car or any car. But I definitely wouldnt want my exhaust hindering my overall output by not having enough flow. Remember that turbo uses exhaust gases, so I'd figure that it might not change the total mass flow, if anything it would decrease it. Hmm...shit dude, I dunno...
. Good luck - hopefully someone else can give you a better answer.