Questions

[jb24 at chrysler.com]

I think I can answer the Volumetric Efficiency questions...

Volumetric Efficiency (actual volume/volume of perfectly filled
cylinder) is somewhat dependent on density of charge.  Momentum effects
should change the filling at different densities (temperatures), but
even more importantly change the pressure wave effects.  So my feel for
this is that part throttle/lean mixture/spark timing should change
exhaust temperature and thus timing of pressure wave events
(differences in sonic velocity).  However, for a given engine, rpm and
throttle position the volumetric efficiency shouldn't change much day
to day (fractions of a percentage most likely).  It's very hard to
predict to many significant figures, that's what testing is for.

As to VE in turbos, VE is measured relative to a reference gas.  If
that reference gas is at the same temperature and pressure as your
manifold, you get a good idea of how your engine is breathing.  If
measured relative to a gas at Standard Temperature and Pressure, the
results are somewhat less enlightening, but let you know how much fuel
to inject.  Mass Airflow Sensors are cool this way - they don't care
what your manifold pressure is, although some richening at higher
pressures is needed to prevent detonation.  Fuels in WWII were rated
this way, relative to isoctane and rich limit of detonation.  Some of
these fuels were in the 140-150 octane range.  Too bad they aren't
available at your corner station. =oP

John Bucknell