Hack
15 Year Member
Yes, experimentation is the key. My Fiesta actually is over 3,000 rpm at cruise 75 mph and gets 39 mpg. Seems like a lot of revs, but it works.To fine my sweet spot, I temp installed a vacuum guage and zip tied it around my steering column. I changed gear/gas to get the most speed with the most vacuum.
Which oddly enough, is in 4th. In 5th(od) The load (even at the same speed as in 4th) Is so great that the vacuum goes to pretty much zero which results in the carb just spilling fuel into the engine. So right now, I dont really use overdrive until I change my rear end gears to something lower than 2.79s .. Keep in mind, with my combo, in overdrive, 80 mph is at 1800 rpms. I am going to aim to get 80 mph up around 2200 rpm eventually.
In overdrive, 80 mph, 1800rpms results in about 12-14 mpg.
In 4th, 80 mph at about 2800-3000 rpms results in about 18 mpg.