I was in Chrysler Engine Lab in 1951 and 1952 and I was
involved in the manufacturer of DeSoto engines (Warren Plant) and
Chrysler/Imperial engines (Jefferson Plant) until 1960.
I remember that Chrysler factory HP ratings were honest
except for the 1960 "slant 6" engines where we under rated the 170 cu. in.
version and over rated the 225 cu. in version. More on that
later.
Rated horsepower in the 1960's was "gross HP". Gross HP is
measured on a dynamometer with lab exhaust (zero back pressure), intake air
corrected to standard barometer and temperature settings and no accessories -
not even a fan. Horsepower as installed in a car would be considerably
less.
In 1960 the new 170 cu. in. engine tested in the
Laboratory at 117 HP but was rated at only 101 HP it because it
went in a subcompact car (Valiant) and we thought the
subcompact customers wanted a 100hp - or less -
engine.
The same year (1960) the new 225 cu. in. slant six tested
at 123 HP but was rated at 145 HP because that
displacement should have produced 145 HP. We obviously had work to do. (A
common cylinder head on the 170 cu. in. and 225 cu. in. versions penalized the
larger displacement.)
Some Chrysler Engineers were upset about this discrepancy
but Product Planners rationalized that it's not so bad when you average the
over rating of the 225 with the under rating of the 170 for the "slant 6"
family of engines.
Burt Bouwkamp