Ugrade /6 or swap to 318

So my car has a /6 in it and ive been contemplating just upgrading that but i also have a 318 lying around and thats kind of my new idea what do you guys think i should do. I had a couple friends tell me the 8 will be gutless and id lose mileage what are your guys' views on the situation and if i go with the 8 what to do to it to prove them all wrong.
:thumrigh: