N1 exhaust vs. custom 240 muffler

[240Stilo]

I was messing around with some numbers and found that i can come up with good performance with a stock looking exhaust for my future turbo. To be exact, my custom exhaust would be everything before and after the muffler. I know by now you're saying "what a dumy....there's nothing after the muffler" well I'm refering to the tips. I was measuring the chrome tips on the muffler to see the area it could give me for exhaust flow if i welded it to the muffler after cutting holes to match. Each of the stock tips are at least 64mm from my not too accurate measurement. The N1 has a 90mm tip. After using the "area of a circle equation" i found that the stock chrome tips (without the middle pipe) would give me 71 cubic mm more area for flow. Now the only thing that I wonder if i should go with 3 inch piping from muffler to downpipe or use 3.75 and follow in the footsteps of the N1 which is already a good exhaust. My aim is for less noise so I'm leaning more towards 3 inches.

All this of course is assuming that the stock muffler is just an empty can that doesn't cause too much turbulence for the exhaust gases.