[Land-speed] exhaust superscavenging

[Dan Wright]

Ray
Some experimenting has been done in the area you asked about.  I was told that
Jim Fueling experimented with a mechanically (rather than exhaust driven)
driven supercharger to forcibly extract exhaust gasses.  He called the gizmo a
"SuckCharger".  Since filling the cylinder with a new charge is the goal, the
suckcharging operation was very fussy about valve overlap.  As I understand
Fuelings experiments, the resulting performance increases were not sufficient
to generate great excitement.

That stands to reason, while the intake charge exists at atmospheric pressure
and temperature (it doesn't have much kinetic energy), the exhaust charge is
(at the moment of exhaust valve opening) pretty excited stuff.  It is at high
pressure and has a great deal of heat energy.  When that exhaust valve cracks
open, the first stages of exhaust gas exodus are highly energetic, and very
fast moving.  Once an object (exhaust gas slug in this case) is in motion, it
tends to stay in motion (inertia).  The best designed headers use that inertia
to produce a cylinder scavenging effect and a pipe scavenging pulse between
sequential cylinders.  That same pressure, inertia and heat energy drive the
turbine side of turbochargers.

These differences between the passive nature of the intake charge vs the
energetic exhaust event are why we see smaller exhaust valves and ports
(compared to the intakes) in almost all engines.

I am sure I have grossly oversimplified this subject, perhaps some of our
flowbench savvy members have something to add??

Dan Wright
"Make everything as simple as possible, but not simpler."
Albert Einstein