HOW TO MODIFY A STOCK DODGE KEGGER INTAKE MANIFOLD Even though this 3.9L V6 intake manifold is smaller than the 5.2L and 5.9L V8 intake manifolds, the same instructions apply to all 3 engines. If you are looking for a few more hp and don't have the money to buy an expensive intake manifold, this modification should cost you less than $50, including the new intake gasket set. I recommend you plan this as a weekend project so you can take your time or pick up another intake manifold at the salvage yard to modify and work on it in your spare time. Once it's complete, all you have to do is remove your stock intake manifold and install the modified one. A real time saver and you've only lost the use of your truck for a couple of hours. These are all the tools you will need to do the job. A Dremel tool (the flex shaft attachment makes it a LOT EASIER but not necessary), metal cutting wheels (at least 10), Ro-Loc 36 grit 2" sanding discs w/ro-loc drill attachment (can purchase at any auto parts store), magic marker or Sharpie, hammer, chisel, metal cutting bits. I purchased a set of 4 metal cutting bits at Northern Tools for $35 but they also can be purchased separately for about $10 each. The cone shaped bit can be used for the entire project but the round nosed bit works better for modifying the injector ports. The long black shaft shown in the picture is an extension shaft that came with a small round Mother's Polishing Ball kit. It's a real time and knuckle saver when smoothing up the rough cuts on the edges of the runners. To use the extension, remove the 1/4" drill shaft from the Ro-Loc drill attachment and screw the sanding disc on the end of the extension shaft. You can also very carefully use the flat side of the metal cutting disc to smooth the edges and save some money. The choice is yours. Stock Kegger intake manifold with the belly pan removed. Notice the old gasket marks on the runner ports. You'll use these as a reference later to open up the ports.
Using a 5/16" drill bit and pliers, slowly turn the drill bit into the larger vacuum ports on both sides of the intake to remove any built up carbon that may be partially block the ports. Using a hand drill here could very easily cause the bit to grab and destroy the vacuum tube. First you'll want to mark the runners using a straight edge (I use a stiff piece of cardboard about 6" long) and magic marker so you'll know where to make the rough cuts to remove the material.
Once you have the runners marked and after cutting about 1/2 of the way thru the runners, you can use a hammer and placing a chisel on the top edge above the cut, give it a few good whacks and the 'to be' removed material will break off. Saves time plus some cutting wheels. Always knock it to the inside away from the cut. Once you have this section of the runner removed, mark the inside runner divider and then score cut.
Remove the remainder of the material. Your intake should look similar to this after all the material has been removed. Remember, this is just the rough cut and the final shaping and smoothing will come a little later.
Using the metal cutting bit in your hand drill, taper and blend the square edge of the top of the runner. Now using the 36 grit sanding disc (with the extension if you have one) sand and smooth the cut edges of the runners while making sure all the edges are straight and the runners are equal in length. Also at this time, sand smooth any and all casting marks and ridges along with rounding or removing any square edges on the inside of the intake. A square, flat edge will cause air turbulence inside the intake and that's exactly what you're trying to remove and increase the air flow to the runners.
Now using the metal cutting bit, taper the inside edge of the runners to a razor type edge. Doing this will give you a completely smooth air flow into the runners. You can use the existing gasket marks around the edges of the ports or use the intake gasket and mark around the inside edge as I've done here.
Now using the tapered metal cutting bit, remove all the excess material around the ports with the sides tapering to the inside. As you've probably already noticed, Chrysler was not overly concerned about making everything uniform and identical from port to port. There will be some areas that can not be smoothed due to this so just be aware of this while working on the injector ports. Using the round nose metal cutting bit (if using the tapered bit, use caution not to go too deep inside the hole as you could very easily mess up the injector O-ring seat), carefully round off the square edges of the injector ports while giving them a slight taper to the outside of the port. There are some casting marks inside the runners so remove as many of them as possible. Your modified intake manifold is now complete and ready to be installed. Personally, I always spray a
coat of high heat paint on the inside and outside of the intake. It's not really necessary, but that's just me. ENJOY and GOOD LUCK!!!