My last #'s on the 87 2.6 turbo non-lockup a/t were about 20 at 75ish cruise on the flats, and about 18avg with a bunch of kickin' it around town/freeway, on regular. Premium added about 2-3 first case and 1-2mpg second case to that because the knock box let it run more advance at cruise with the higher octane.

At the 75ish cruise, I was seeing about 200-300rpms of converter slop that a lockup would have prevented. It ran at about 1-2psi of boost at that speed and load.

Not responsible for advice not taken...