"J. Clarke" wrote in
:

'60s American cars had no shortage of horsepower
and nothing changed in the laws of physics to
change that. What changed was the law. The
electronics let a car that is in compliance with
the new laws produce as much power as one that
was produced before the laws went into effect.

Sorry ol' buddy, but krw and clare are right, the law
has nothing to do with it. It is all about the laws
of physics, specifically those relating to thermodynamics.
60's era engines were lousy at thermodynamics (and tried
to make up for it with vast displacements).

Modern engines have overhead cams and much "cleaner"
intake manifolds - result is much better airflow into
the engine. Modern engines have fuel injection -
which means the exact right amount of fuel for best
combustion, 60's engines had carbs, which just gave
a rough approximation of the right amount of fuel.
Engines today have knock sensors and electronic
ignitions, which means you can have higher compression
(better thermodynamically) and the spark occurs at
the optimum time for mechanical advantage (you want
peak cylinder pressure with the piston about 1/4th
down the cylinder, for best leverage on the crank).

All these things (and that doesn't even touch on
variable valve timing and turbos and other exotica)
mean engines today produce twice as much power per
cubic inch displacement as 60's engines did. They
are far more powerful than those dinosaurs.

John