I'm still in the process of building my Z so I can't chime in on this just yet, but I am curious to see how other projects have turned out. Obviously, we're not building these things for hypermiling, but I would imagine that with the right gearing in such a light car, that some are seeing relatively good fuel economy for a v8 powered car.
My thought is to create a thread where people can post their numbers up just to see what our cars are getting. Post up any relevant info as it applies to fuel economy (i.e.:engine size, carb or efi, etc.). Get as detailed as you would like regarding driving conditions.
I'll use my truck as an example of what a good post might look like since the z isn't running yet.
1999 Dodge Ram 3500 2wd Dually
Engine: 5.9L ISB Cummins
Transmission: NV4500 w/US Gear O/D
Rear end ratio: 4.11:1
Additional info: Edge tuner, upgraded wastegate, Banks 3" exhaust
Observed fuel economy: 24mpg cruising at 60mph in 5th gear with the overdrive engaged
~16mpg around town
~15mpg towing roughly 10,000lbs at an average speed of 55mph in 4th gear with overdrive engaged