10 Oct 1997 02:22:58 -0700
Robert Harris 
Subject: More Vizard head aches

Per David Vizards "How to build Horsepower, Vol 2

"As far as derivability and low end output is concerned, especially when a
larger cam is used, a system with a butterfly in each runner is preferable to
open ports and a plenum situated butterfly.  Unless a fuel injection system
with port-situated butterfly is used, the carbs will outperform the fuel
injection.  The reason for this becomes apparent if we study what happens when
a common set of butterflies controls the air for a number of cylinders.  When
the butterflies of a common plenum V8 system are closed, the manifold will be
subjected to the vacuum drawn by the induction strokes of the pistons.  When an
intake valve opens, it will initially be in the overlap phase, so the exhaust
valve will also be open. Since all 8 cylinders are connected to a common
plenum, one of the other cylinders will be at peak draw about half way through
it's induction stroke. This cylinder will find it easier to draw the exhaust
from whichever cylinder is in it's overlap phase, than it will to draw air
through the almost closed butterflies of the plenum air valve.  This means that
if low-end output and good manifold vacuum are required, the duration of the
cam for a plenum type system must be kept shorter than for a system with port
located butterflies.  The need for a shorter cam on such a setup, as for, say,
a typical 350 CID V8 can cost as much as 50 horsepower.  With a system having a
butterfly located in each port, one cylinder cannot influence another.  As a
result of this the intake valve, in it's early opening phase, experiences far
less vacuum than in the case of the common plenum.  This allows the engine to
use a much bigger cam before low speed derivability becomes unacceptable."

"Going hand in hand with improved low end output is the superior idle quality
produced by an IR system compared to a plenum system.  The reason for this
becomes apparent when we look at engine vacuum at idle.  When  a number of c
ylinders are joined, as in a typical single four barrel induction system, the
plenum volume is drawn done to a partial vacuum.  If there is a significant
amount of overlap, then a cylinder just starting it's induction cycle connects
the entire intake system to the exhaust via the overlap.  Because there is a
partial vacuum in the intake, a certain amount of exhaust will be drawn into
the intake and pollute the incoming charge.  This necessitates increasing the
idle speed and richening the mixture to compensate.

With an IR system, the vacuum created in the runner, largely exists only when
the piston starts it's downward stroke.  Prior to this, there is, compared to a
plenum type intake, almost no vacuum existing in the intake port during the
overlap period.  As a result, reduced exhaust pollution of the intake charge
occurs from this source.  This means that the idle mixture used, can be much
leaner as the fresh charge is more easily ignited.  Also, the ill effects a big
cam can have on part throttle operation at low RPM, are substantially reduced.
It is not uncommon to achieve a smooth 600 RPM idle on a V8 equipped with a
moderate race cam."


So now reading Vizard give's headaches.  Then he goes on to discuss helmholtz
resonators, and tuned intake pipes feeding the resonator.  Suggests 8 count
them 8 oxygen sensors as the only way to tune an engine - lumps plug reading
with chicken entrails.
Then there is this little tidbit about what happens inside a manifold

"To demonstrate the complexity of successfully managing air and fuel
interactions, some tests run at Iskenderian Racing Cams are worth relating.  In
an attempt to even up the mixture between cylinders, air valves were installed
in those runners that were carrying a rich mixture.   The intention was to
bleed air into these runners to compensate for the richer mixture they carried.
In an effort to achieve the best results these valves were positioned as close
to the cylinder head as possible.  When put to the test, it was found that
opening any one air valve resulted in all the cylinders running leaner.  This
demonstrates that the air moves around within the intake manifold far more than
might normally be supposed and that any one cylinder can pull air from as away
as halfway down the runner of another cylinder.  With interactions as strong as
this, it becomes easier to understand why uniform fuel distribution is not the
simplest of goals."

Apparently, what I draw from this, is that butterflies near the port, one for
each cylinder, make the most usable range and power.    Thinking maybe an old
Hilborn with Pulse injectors instead of continuos jets, and a GM TBI
controller.  Long Ram pipes connecting into a plenum - helmholtz resonated.
Since SB42 passed, maybe gas aint so bad for the stang - but I still like
propane!!!!!! At least it's still in the mix.  And a must for the RV

Damn, I really want them butterflies down by the head as Dave Vizard suggests.
Oh well, read more, have plenty of time to ache this out. Too many options,
not enuff bucks - back to finding a job or starting my own political party (The
American Crud and Corruption Party - We can be bought!) and then financing the
project.  When I blow this state, hope to start something making money in the
real world.



13 Oct 1997 06:08:05 -0700
Robert Harris 
Subject: RE: More Vizard head aches
'Dave Williams' 

Books Name is "How to build Horsepower - Vol. 2, Carburetors & Intake
Manifolds"
ISBN 1-884-089-14-3, Part SA52 - Summit has it for just under 15 bucks
It's very recent as he refers to 1996 dates thru out the book.

Don't lose the plenum.  Thimk add butterflies.  Looking at a 5.0 lower
manifold, with the right tools it might not be too hard to add butterflies -
just below the split for the upper manifold.  Depending on which manifold you
are using, one or two shafts would be needed to be drilled.  Carb brass type
butterflies could be made out of sheet brass.  Connect the TPS to the new
shafts, replumb the vacuum lines correctly - viola - the best of both worlds.
At part throttle, the butterflies isolate each cylinder - drawing from an
atmospheric pressure "plenum" instead of a throttled partial vacuum plenum and
such behave as an IR system.  As airflow demands increase, the throttle opens,
and now you draw from the tuned lengths and plenum.  This would of course make
an extremely lethal setup - almost not fair and certainly not obvious,
specially if the throttle connected to the butterfly shaft(s) at the back of
the engine.  How much is a 30 degree duration spot worth at the stop light???
Plus I suspects the air flow sensed would be much smoother since the pulse
hammering against the throttle is way downstream.  Butterflying it would also
go a long way to cleaning up part throttle mixture imbalances.

Polish the shit out of the OUTSIDE of the manifold.  Vizard states that most of
the cooling gains of outside air are lost as the air is re-heated in the
aluminum intake manifold.  Polishing the outside radically reduces the surface
area and as such, reduces the heat gain from under the hood and delivering
cooler air to the cylinder.

In my case, I'm back to thinking 351 Cleveland 4V using a 302 EFI.  Have to use
an inch thick spacer anyway, may as well fabricate a butterfly assembly in the
spacer.  Stroke the shit out of it (400M+).   Still, I like the 429.  Oh well,
brain ache as the research continues.