Turbos and Blowers

[Gary Derian]

The Miller cycle is more efficient because it has a high expansion ratio.
The inlet closing is delayed so compression doesn't begin until late in the
compression stroke, thus the appox. 75% Wayne mentioned.  Now a very high
mechanical compression rato can be used as the actual is also 75%.  The
advantage is a high expansion ratio.  The disadvantage is a loss of power
for a given engine displacement.  All it takes to convert any engine to a
Miller cycle is a cam with a very late intake closing.  These cams were
popular after the first oil shock to improve fuel economy of older high
compression engines and allow regular fuel.

Gary Derian <gderian at cybergate.net>

 From: Wayne Blair <wayneb at foxln.com.au>
>By example the Miller Cycle engine which is a normal 4 stroke with very
>unusual valve timing (in the main very late exhaust closing) which NEEDS a
>blower to run properly. These engines are about 75% the capacity of a
>normally aspirated engine of similar capacity. The reason for the higher
>efficiency is --- the smaller size of every thing , thus smaller surface
>area to absorb heat (and be passed on to atmosphere via cooling system) and
>so the extra heat is used to push the piston down there are many other
>efficiencies related to size eg windage etc. This principle is similar to
>STEAM engines and the good old GM 2 stroke diesel which makes good
>efficient power for weight but can do little more than idle with out the
>blower. An Australia designed engine also uses a similar blower dependent
>design ( http://www.orbeng.com.au ). This is real and why MAZDA (i think)
>are using this engine in some vehicles. In general the smaller weight and
>size of the power plant allows for better handling, more aerodynamic,
>faster cars.