When mine was a DD, I'd get around 20mpg highway. 400/4spd with stock 6x-8 heads, 3.23 rear, 744 cam, torker 1, qjet and headers into 2.5" dual exhaust and lots of timing (38 total plus full vac advance). I left primary jetting stock (lean) and richened the secondaries to compensate under WOT. It worked well with the open plenum T1, when cruising around I'd be running really lean and get good mileage but when floored the secondaries would compensate.
I switched to #16 heads and an early iron intake with everything else the same and economy is down but it hasn't been tuned yet, so I attribute it to that, at least partially. The timing is down to around 32 degrees until I get the carb tuned (way too lean on primaries and no open plenum, so I know the mixture is uneven under WOT).
|