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Lower Intake Port Matching


Low Buck HP in a weekend!  


This article assumes you have removed the Upper Intake and it has already been Port Matched.

Once again:
Follow the "DIY" Link!

Make sure you have read and understand the Standard Abrasives site before proceeding.   Read it over a couple of times, print the pictures and post them above your computer's monitor so they sink-in!
Tools and Materials:
This is an average 3.0L intake runner...

Not exactly conducive to a High flow race engine.   Remember, for our 7,000 RPM goal,
we must be able to flow over 360 cfm or 60 cfm per port.

This is after an 80 grit drum...

Final finish will be as smooth as possible.   On carburated engines, you would stop here, the minor turbulence is needed to keep the fuel from puddling.   For our port injected engine, which is "dry" until the heads, we want it smooooth!   I finished all ports with a Dremel Tool (it was the only thing I had that could reach!) and 120 grit drums.  The final look is similar to brushed or satin aluminum.

Modified port versus Stock...


(Maniold is upside down) I cut to within 1/16" of stock gasket to avoid cutting too much material and destroying low end power.  It is imperative that you properly align the gasket to the manifold or you will create a mismatch when you port your head.  The 3.0L uses an ingenius locking tab design to keep the gasket in the proper relationship between the head and manifold.  Work with it a couple of times to gain an understanding of how it works before you try to align it on the lower intake.  Use stock bolts in the holes to help with the alignment.  The amount of excess material is amazing, but it goes away quickly!  Just keep the ports and cutters well lubed to keep the aluminum from clogging them up.  There is a small bump on the upper wall just before the injector boss.   I wacked it flush and have had no problems.  It appears to be like the "EGR" bump in the 2.9L exhaust.

Lessons Learned:
Here is what I learned from this experience:

Make this a swap job!
Buy another manifold ('97 and below owners, get a 98+ upper and lower!) and finish it completely with all the mods listed below.  Then set the time aside to do a weekend swap.  My truck was down for 5 days and took well over 14 hours to finish.  A simple manifold swap would have taken less than 8 hours to complete.  I'm going to get another lower intake and start work on it.  It will be used as an exchange service and come complete with matched and blueprinted injectors!


Build a "Valley Pan"!
Hot oil splashes up on the bottom of the intake, warming the incoming air.  Fashion a thin gauge aluminum pan to protect the underside of the maniold.  Use 2 or 3 self tapping sheet metal screws to fasten it to the rail that runs down the center of the manifold.  For an example, look at the old Pontiac V-8's or a 351C engine.

Heli-coil every threaded hole in the manifold!  
"O.K., just thread those steel bolts into the cast aluminum manifold".  Riiiight.  Who's "better idea" was this??
Not the way to do things.  From what I saw inside the engine, this is the first time the lower manifold was pulled, and 3 of the threaded holes were showing signs of fatigue.  DIY with a drill press and a tap, or have a machine shop install them for you.  You will need 4 different sizes; 8 for the valve covers, 6 for the upper intake bolts, 4 for the fuel rails and 2 for the thermostat housing.  (will post sizes the next time I have the intake off)

Make fuel rail spacers!
The fuel rail is bolted directly to the manifold and heat travels right to the fuel.  Not good.  Make 8 spacers out of 1/8" G-10 or G-11 (the same Phenolic Material you used for the Plenum Spacer).  Use the fuel rail mounting tab as a pattern.   4 go between the intake manifold and the fuel rail mounting tab and the other 4 go between the fuel rail mount and the attaching bolt's washer.

Insulate the fuel rail!
Use any good quality thermal tape to loop around the rails.  Sleeves won't clear the injector seats and you can't separate the rails to slide them one.   Use a 50% overlap and cover everything except the injector holes.   Use sleeves to cover the supply and return hoses all the way to the fuel filter.

Tap the rear coolant passages!
The amount of corrosion I found at the back of the heads was unreal!  Drill and tap the manifold to add UNC Pipe to AN adapters and plumb with Braided Stainless.  Run the lines to the front of the engine and build a simple thermostat riser to plumb them too.  This allows fluid to flow from the back of the heads (reducing corrosion) and still allow the t-stat to regulate the temperature properly.

Change out the injector o-rings!
You already have them out so it's cheap insurance.  Better yet, replace the injectors with a matched set!

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