Hudson, Lincoln, Nash, and Mercury
Equipped only with standard transmission and drive gear ratio, the Mercury established a remarkable stock car economy figure of 23.35 miles per gallon which bettered the marks of 15 of the 22 other finishing cars, a majority of which carried overdrives. Mercury consumed no oil.
The Lincoln won, Marshall Martin was the driver
read all about the Gilmore years online in the Google Books:The Mobilgas Economy Run: A History of the Long Distance Fuel Efficiency ...By Dave Hermanson