"Bernd D. Ratsch" wrote:
>
> Where? I looked on the DML home page.
I went into the Archives and copied it, here it is:
what Ive done to my Intake manifold
Magnum Manifolding
The dry manifold is an entirely different animal than its counterpart.
The reason being that air traveling by itself in a dry manifold can make
all
sorts of turns that would be impossible for an air/fuel mixture. Wet
manifolds having abrupt runner turns or irregularities separate the fuel
from
the air. This in turns leans out a given cylinder. Trying to get the
same
air/fuel ration in each cylinder tuned with a lean runner condition like
this
is next to impossible. Builders will then epoxy in popsicle stick dams
or dig
trenches on the plenum floor that lean down all the runners just to
create a
balance. The end product is far less than perfect.
Fuel separation maladies just plain don't happen in a dry manifold. The
injector, suspended from the roof of the port, aims at the valve head,
insuring the correct air-fuel ratio in each cylinder. Most dry OEM
manifolds
have large plenums to supply the cylinders with enough air and long
runners to
generate torque. This combination of long runners and big plenums is
great
for gas mileage and bottom end power, but does not lend itself to
performance.
Even though the OE Magnum manifold falls in this category, it's easily
modified and shows substantial horsepower improvements when worked on.
One
inexpensive revision that aids upstream air density is the fabrication
of a
lifter valley heat shield. Magnum manifolds have a flat steel cover
bolted to
the underside machined surface. It sits just above the lifters. The
plate
becomes absolutely torrid when the engine is up to operating
temperature.
NHRA truck class racers bend up a piece of steel plate the length of the
manifold cover and weld it into place. This shield acts as a heat buffer
by
isolating hot splattering oil and rising heat away from the manifold's
bottom
cover plate. Because the factory cover is not getting direct exposure
with the
shield in place, air in the manifold stays cooler (denser). Cash outlay
should run under 25 bucks at your local welding shop (plus new gaskets).
All
you need is a flat piece of steel stock, 1/16-inch thick, bent at the
ends,
and welded into place. Have the shield welded 1/2 to 9/16 of an inch off
the
valley cover and you're all set for the dance. Though it won't up your
HP
figures, it will allow you to run more consistent times on hot summer
days.
This mod also helps prevent pre-ignition in street trucks that see
engine
temps soar when hauling heavy loads.
While your V6/8 Magnum minifold is off, the next performance step is to
shorten the runners as much as possible and cut two inches out of the
plenum
divider. This mod will add about 10/12 HP to your engine and raise your
shift
points about 300RPM. OE castings are made from some pretty tough
aluminum,
and buzzing away with a grinder can get tedious. A better way to go
would be
to have a machine shop mill the runners flush to the castings port
floors,
then get in there with your grinder to clean things up. Finish touch the
runner mouths with a polished radiuses so turbulence is minimal. None of
these grind/olish/weld V6/8/10 modifications require a high performance
computer because factory computers require a great deal of latitude to
cover
everything between lean high altitudes to rich seaboard environments.
Lastly, there are two Magnum precautionary notes. It's common for
Magnums
to blow the gasket that seals the cover to the manifold. You'll know
when
that happens because the performance will slip off par, or you may begin
hearing pre-ignition knocks. Lift your hood, remove the air breather lid
and
look down the throttle body. If the venturis are dark, sooty, or oily
looking, your engine needs a new cover gasket. What the heck, you can
modify
the intake while it's off. When you finally replace the cover and
gasket, be
sure to put silicon on the cover side of the gasket and use a fixative
on the
bolt threads. The other concern centers on the lifters. They're real
heavy
and overcome the strength of the lifter bore casting at high RPM.
Spinning
the Magnum to 5400 RPM is borderline, 5800 RPM too much, and above 6000
RPM
can be the kiss of death. What happens is the heavy lifters crack the
casting, start to wobble, and the valve train self-destructs. When the
valve
train starts to go bonkers, you'll notice an upper RPM vibration, almost
like
the engine is out of balance. Either limit your shift points, buy a
Fluidampr, or pray somebody develops a lightweight lifter for the
Magnum.
Magnum plenums are extremely large. By taking up some of the volume,
resonating effects (powerful pressure waves) are increased, augmenting
low end
torque. And, because the Magnum's not a high RPM engine to begin with
the
high end is not affected. This is an involved process. The high dollar
route
would be to buy four quarts of Devcon and fill each corner of the
intake.
Besides being expensive Devcon is heavy. Another approach is to scrounge
up
some 1/4 inch plates of quality aluminum, make some cut outs from
cardboard
that, when heliarced in, box up plenum space in the manifold. It's time
consuming, but seems to work. Magnum V8's really respond to this plenum
reduction plan. Even though the V6 has a smaller plenum to begin with,
resonation is much greater than a V8. Nonetheless, power increases with
a
plenum reduction.
The intake manifold is probably the most underestimated piece of
performance equipment on the engine today. When modified with even
simple
changes, it responds unbelievably well. Though some of these alterations
can
get quite expensive, a bucks-down performance aficionado can still do
quite a
bit on a Saturday afternoons tie span. Though the new millennia will
undoubtedly bring further developments in the intake manifold, on
thing's for
sure; as long as the internal combustion engine is around, it will
always have
need of an intake manifold.
Mopar Muscle--Inductive Reasoning July 1997
Eric
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