A few have been curious as to Eric's write up in Mopar Muscle
Magazine about the stock magnum intake. Here it is and thanks Eric!
GS -
98 5.2L 5spd
MOlsze6480@aol.com wrote:
> Is there a write up on this some where ( the porting I mean ) ?
> Thanks in advance, ML
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Rekker21@aol.com wrote:
> 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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