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00+ Northstar Intake manifold...why so filthy inside?

1624 Views 9 Replies 4 Participants Last post by  Submariner409

After wrestling with the crossover gasket job, I was planning to change the plugs while the intake was off for that fiasco.

Unfortunately, the car got the best of me in round 2 and I decided to surrender to the plugs for another day.

Since I had the intake off, the plenum boot and seals were going to get replaced as well. Low and behold the throttle body was filthy and so was inside the intake manifold.

I guess the egr and pcv system work wonders to the inside of the intake manifold. Nonetheless, I thought this just might be the case maybe just with my car. So, I decided to head to the men's mall, since there was unfortunately a fresh kill on the list and try my luck.

Well, there was a nice 2002 with brand new strut in the front , brand new air shocks in the back and an overheated engine. Another fatality, anyway it dawned on me to retrieve the pcv hose on the back of the intake.

Interesting the things you find out when searching for other parts. Like the clip that holds the hose to the intake manifold was missing on mine.

So intake hose in hand I decided to peek inside this intake manifold, sure enough filthy. I wondered why in the world is this thing getting so mucked up. This can't be good for induction...... I took the whole manifold as a spare.

I will disassemble the manifold, thoroughly clean it and mount it to the car when swapping the plugs and then clean my original one later for the next time I remove the manifold.

Yet, this time I will monitor how long it takes to get that bad and what steps I can take to prevent it getting so filthy......
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Not a problem. If you had the manifold off you know that the PCV dirty air line goes to the center tunnel on the 00+ manifold. The crap that passes through that large vacuum bleed would astound you. The oily film is of NO consequence.

EGR has very, very little to do with the oil vapor film.

Be careful - that PCV system involves a very calibrated air bleed into the intake manifold and sometime in 2000 or 2001 the PCV "valve" changed from the older rattle type to a fixed orifice - different bleed rates. And a PCV rattle valve or fixed orifice is engine-specific: You must replace it with the correct one for THAT engine.

EDIT: Overfilling the oil level on these engines is a large contributor to intake manifold and throttlebody slime. These are port injected engines, so there's no fuel wash through the manifold runners - only air and oil vapor. If your Chevy 327 was port injected it would be just as slimy.


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Not enough air flow under most driving conditions to accomplish that.
Truth ^^^

Even at 70 mph on I-95 southbound the throttle plate is only open 8 - 11%. "Airflow" through the intake manifold is practically non-existent. That 14.7 psi of atmospheric pressure does pretty well at forcing air into the engine at those speeds, and max intake airflow only occurs at WOT - and for a 280 c.i. engine that's not a lot, in the order of things. heck - manifold vacuum at 70 mph is up around 16 - 19". A perfect vacuum is 30", so our engines run MOST of the time at 2/3 of possible vacuum. Not much airflow there. Atmospheric pressure can only force so much air into the various passages, openings and volumes of an XXX engine. NA engines DO NOT "suck air" - it is forced in by atmospheric pressure at a rate determined by throttle opening = power demand.


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Here's some homework - Airflow requirements for NA engines.

VE = Volumetric Efficiency,
CFM = Cubic Feet per Minute,
CID = Cubic Inch Displacement,
NA = Normally Aspirated.

CFM = CID X RPM X VE / 3456

(Use a VE of ~80% (0.8) for NA engines, stock.)

So, the 279 c.i. Northstar, tooling down the Interstate at 70 mph, 2000 rpm - needs 129 CFM. Not much flow there.

279 X 2000 X .8 / 3456 = 129.
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Please go back and study your high school physics.

Atmospheric pressure forces air into a vacuum at a rate determined by the size of the entry orifice - in this case, throttle blade opening. The only "positive displacement" is the result of internal combustion created by burning a fuel/air mixture to create expanding gas which results in a power stroke and the necessity to remove the spent excess gas at the end of the power stroke so the cylinder process may begin again.


"But, Sub - How come earth's atmosphere doesn't escape into the (almost) total vacuum of space ???". Gravity. The reason that the atmospheric pressure (weight) of a column of air is 14.7 psi at sea level.

later EDIT: here - Wade through some of this.
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