Classic/Antique Car Repair: Fuel economy, rear axle ratio, oxygenated gasolines

Question
Can you please tell me what to expect  in MPG for a well tuned 1947 Packard
Clipper 6. I understand the Clipper 8 gets @ 16 Mpg and would assume the 6
would get maybe 20 or better.

Answer
If the Clipper 6 has overdrive, I'd expect about 18 MPG at a steady 55-60 MPH in flat terrain, if you drive it conservatively.  If you don't have overdrive, don't drive it over 50 except for short bursts, and expect around 16 in that service.

There were two different 8 cylinder motors in 47 - the 282 and the 356.  The 282 did somewhat better on gas than the 356, although the difference is small.

The cars don't get as good mileage as they did when new, because the modern oxygenated gasolines don't provide as much energy as the old gas did.

I drive a 47 on long trips, with overdrive, but I have changed the rear axle ratio to improve mileage. My car is a limousine with the 356 engine, so it is quite a bit heavier, but I get 17 on a trip with it consistently.  I drive 60-65 with it.

Dick