Some Compression Ratio History

[n9ads@domain.elided (Howard R Pletcher)]

I checked out some old Motors Manuals covering 1935 cars.  In 1935,
typical compression ratios were in the 6 to 7:1 range.  The highest I
noted was Plymouth at 6.7, Ford was 6.3.  The lowest I saw were Willys
and Bantam at 5.1, but surprisingly Buick and Nash used 5.25 and
Chevrolet 5.6:1 while all others were above 6.

Going back a little further, the 1932 Ford Model B featured a ratio of
4.6:1, up from the 4.2:1 in the Model A.  The first 65 hp flathead V-8's
featured a 5.5:1 ratio.  I don't think the ratio went much lower.  I
found references to early Otto-cycle engines in the 1880's having a 4:1
ratio.  Rudolph Diesel designed for 30:1 for his first engine in 1893,
but had to settle for 18:1 due to leakage past the rings and valves.

By 1951, almost all cars were in the 6.5 to 7:1 range.  The 1955 Ford V-8
was 7.5:1 and the Chevrolet 265 was introduced at 8.0:1--no wonder it was
considered a hot engine in its day.

A quick glance at some of the truck engines of  1935 showed 5.5:1 to be a
typical number for them.

Howard Pletcher
Howteron Products Scout Parts

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