attached JPEG picture is a graph of a typical 1960s automotive engine performance map with
BMEP
(brake mean effective pressure which is similar to torque per cubic inch of displacement)
plotted against
Piston Speed in Feet per minute
(convert to RPM using stroke in feet instead of inches)

From Volume I of Charles Fayette Taylors classic book on engines "The Internal Combustion Engine in Theory and Practice" figure 12-16.

Modern engines have improved about
7% in fuel economy BSFC for each ten years,
so the ovals of best fuel economy
would be smaller numbers than the 0.500 pounds of mass per horsepower hour here,
except that this is for "pure" 120,000 BTU per gallon gasoline
and today it it blended with ethanol
down to as little as
107,000 BTU per gallon in some winter blends.

The upper line for BMEP
which tops out in this 1960s data at 120 psi, would now go up to the
138 psi to 160 psi range.
Seems like I remember that both the 1995 cast iron Magnum 8L V10 and Magnum 5.9L V8 maximum torque values calculate out to about 138 psi.