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jk - i'd say 74 mm on a 3.2 is fine. Porsche did it on the 987 3.2's and the 2004 special edition 3.2.
if you are feeling sporty, pull out the mechanical engineer in you: 3.2 litre engine displacement = 1.8 litres / rotation = 12,600 litres / minute at 7000 rpm = 210 litres / second = 0.21 cubic metres / second.
now you have three options for the size of path you want to push this air through:
inside diameter of throttle body:
986 = 67 mm = 0.0035 square metres
99x/987 = 75 mm = 0.0044 square metres (some say 74 mm, some say 76 mm; I used 75 mm)
GT3 = 83 mm = 0.0054 square metres
from here you can calculate the velocity of air in each case (unit analysis says simple division should work):
986 = 60 metres / second = 216 km / hour
99x/987 = 48 metres / second = 173 km / hour
GT3 = 39 metres / second = 140 km / hour
not sure what this tells me. I do know that it would take a heck of a lot less work to accelerate air to 140 kmph than 216 kmph. also more opportunity for ram air benefits with the slower airflow. but I presume there are other things at play; restrictions at the intake manifold itself, low rpm trade-offs, intake tuning effects, etc.
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