[aerohead]

I a late 1970s SAE Paper about the Shell Mileage Marathon of earlier times,they showcased a 1920s Chevy which used lighter valve springs for their engine strategy.It did lower the useful rpm of the engine,but they topped out at around 55-mph coasting downhill and averaged in the 20-mph range over the course.
A metric which would be interesting about springs would be their hysteresis.
Unlike the rubber of a tire on a paved road,a steel valve spring may have virtually zero physical distortion during service and whatever power is used to open the valve may be almost completely liberated when the valve closes.
A stronger spring requires more effort to compress,but it returns most of that back?
PS I was shocked at how much effort it took to hand rotate the camshaft on the CRX.