I'm trying to educate myself on installing a turbo with my 250 in my '68 Camaro. It'll be a street setup, bored 0.030", mild cam, improved exhaust and intake, TKO-500 or T-5 trans, 3.08 gears. Probably will be staying between 1500-3500 RPM. Looking for decent MPG (20+) with as much HP and Torque and fun as I can economically get. I have a few questions.

1. Will a turbo increase or decrease MPG?
2. What kind of cost am I looking at?
3. What improvements in HP and Torque should be anticipated?
4. GUT CHECK,,,,,is this a good idea considering the parameters of my plan discribed above?