Fool Economy

I have a ’73 RR with a 383/727 combo that was rebuilt recently by a local Mopar guy. Honestly, the thing runs great—12.90s @ 108 with 3.23s in the rear, but the fuel economy absolutely sucks, like 7.5 mpg. Of course I never expected this thing to be an economy champ but I was figuring on at least 14‑16 mpg. In talking with the builder, his response was simply you gotta pay to play, but c’mon. Here are the build specs hopefully you might be able to spot a problem or point to a solution: 383 w/Eddy aluminum heads and 9:1 comp, Comp Mopar hydraulic .525/.525, 230 @ .050; No vacuum advance on distributor, everything done mechanically (36 deg total timing); Lupo built 727 w/3800 stall (I’m actually going to put my old 3200 Turbo Action back in because I hate the street manners of this converter.) My thought is that the converter and the lack of vac advance are the two major factors especially since this car is street driven, but the builder doesn’t agree. Your thoughts?

I agree with you 100% on both points. To get any kind of reasonable fuel economy, you need a total “cruise/light load” advance of well over 50° BTDC—usually, closer to 55°. No way to get this without vac advance. (’Course I think 14-16 MPG is a bit optimistic.)
You also need an O2 sensor; you may be able to lean the primaries out a ton.
All of the above also drastically increases engine life. (Think: no more unburned fuel washing oil off the cylinder walls.)