"cmyr" wrote in message
...
Going back to some hot rodding roots,I believe V.E. was increased
in the late '60's-70's thru the use of a specially designed double
cone affair placed in the collector pipe of a tuned exhaust
system,which created a stronger vacuum effect , creating stronger
scavenging of exhaust, and to some extent , helping draw more fuel/air
mix into the cylinder.

There have been a number of things that improved VE: Generally, higher
compression ratios help especially at higher RPM, roller tappets seem to
withstand much faster ramp angles and can stay open further during the open
part of the valve cycles, and anti-reversion cones in the exhaust are said
to work very well in the mid-range of RPM for any given four cycle engine.
In addition, intake and exhaust port shapes play a major role; as do other
aspects of head ad piston crown design.

In a nut-shell, there has been a lot of progress over the past three
quarters of a century, and the only place that I can think of in which
aircraft engines have led the way has been in the area that we used to call
"blue printing" in which the ports are more carefully caste, machined, and
finished to closely match the design drawings for the engine. Today, every
late model engine that I have seen is done that way at the factory; but
forty years ago, automotive engines were really crude.

Peter