76 w/5spd, 80mph and below 22-25(about 350 miles per fill). Over 80, forget it!

to Sailorbob, with the four speed my 60mph rpm range was 3k after 5 spd, 2250.

I can't say what increase in mileage I got, but it sure made cruising a lot nicer.

I've done several at home. All I ever use is 4 tall jack stands and a transmission saddle on my floor jack.

Its kinda funny how the stock & modified Zs are getting about the same mileage.

my 78 (flat tops, big TB, 6-1 header, 4 speed) gets around 25-27mpg highway. It has a tendency to get right around the same mileage if I drive like a granny or if I pin it everywhere.

my old 72 with a crown turbo kit got about 18mpg (with a 2" Jag SU)