I consistently get 16 mpg with my slant in a 68 dodge dart 2 door H/T with a 1976 OD 833.
I am kinda a lead foot and with a slant you have to be a lead foot to push it to keep up with today's traffic.
Don't expect much from a slant, sure it's only a six cylinder but it's also a heavy and very old engine that was designed to run at 55 mph or less, more so on the less part.
Motor trends lil replace the stock exhaust with 2 1/2" pipe added 9 rwhp. I did that & now I dont have any issues merging into freeway traffic.
Back on the Tune Time Performance dyno revealed we picked up 9 rwhp and 10 lb-ft at peak. Maximum peak horsepower moved up from 2,900 to 3,500 rpm. Peak torque stayed at 2,900 to 3,000 rpm. Each pull was made from 2,500 to 4,200 rpm
