This is from Sighard Hoerner's book,"AERODYNAMIC DRAG",that Hoerner self-published in 1951.
In 1935,Hoerner got hold of this small DKW,pulled the body,and replaced it with Jaray small saloon body (Later verified @ Cd 0.245 ).
*As a convertible we see Cd 0.85 and top speed of 49.5 mph with a 20-hp engine.
*With the top up,drag falls to Cd 0.64,and top speed climbs to 53 mph.
*With the Jaray body the Cd drops to 0.44,and top speed goes to 58.2 mph.
*Adding a full belly pan,Hoerner gets down to Cd 0.25,with a 66.7 mph top end.
*I guestimated a power line for Cd 0.13 (full-monty) and it looks like she might have done 72.5 mph.
This car was selling in England at the time with an 8-hp engine,and was guaranteed to deliver 45-mpg at moderate speeds.
At Cd 0.13 she might be looking at 48.3 mpg at 72.5 mph if the BSFC is maintained with gear-matching.
A Chrysler was similarly modified with the Jaray body.Alex Tremulis reported significant increases to both speed and mpg.
Chrysler's own research in 1934-1/2 had cut drag by 50%,coming in at Cd 0.244
So with today's Tesla S we've caught up with the mid-1930s.It will be interesting to see if we'll ever get to 1922.
