Porting and Shortening a Stock Upper Intake
tmoss
I get inquiries about porting the stock upper intake. The restrictions in the upper intake are its runner length, throttle body runner bolt bosses and 63mm throttle body opening. Since this article will address things you can do at home.
The throttle body runner opening is 63mm from the factory for the stock 60mm throttle body. If you need to retain the EGR spacer and want to run a 65mm throttle body, the opening needs to be opened up to 67mm as that is the size of most “65mm” EGR spacers. If you are going to bolt the 65mm throttle body directly to the upper intake via a EGR spacer, you may also need to open the runner to its inside diameter. This is a relatively easy thing to do with stones, paper rolls or carbide bits. Just remember that each 1mm taken from the circle will add 2mm to the diameter, so to go from a 63mm stock opening to a 67mm opening requires that 2mm needs to be removed from the circle edges. I do this free-hand with a carbide double cut bit (SF-3L6 DBL) that can be purchased at www.carbidebur.com for about $15. It does not take a lot of time. Just be sure to keep the bit moving around the inside diameter of the hole so that material is taken off evenly. You must use leather gloves and support the front half of the bit with your gloved hand while porting the runner opening. The long bit will be used deeper in the runner to reduce the bolt bosses.
The next area that can be opened to allow less turbulent air flow is the TB runner passage. The two center intake bolts create a narrow “S” curved flow path past the bolt bosses. Below is a picture of the bolt holes that give an idea of how the air must pass. When viewed from the TB opening, the straight through cross section can be seen.
To open the throttle body runner between the bolt bosses you will need a machinists square, a machinists ruler with 1/64” graduations preferably, and a metal ice pick or other scribing tool.
The inside bolt diameter and the inside runner wall reference points must be brought to a common point for measurements during the porting process. Below is a picture of a 3/8” bolt placed SQUARE in the bolt hole and the machinists square that is pushed up to the TB flange face. This brings the inside diameter of the bolt hole out to the flange face. Mark the spot with a scribe.
Use a Sharpie permanent marker or blue dykem to drop that marked point vertically down the throttle body flange face of the intake. Next, do the same procedure to find the runner wall and bring its reference out to the flange face. In this particular case, the edge of my machinists square aligned perfectly with the black sharpie mark edge from the bolt hole. This is a coincidence and may not be true for you
Notice that there is a distance from the ruler edge to the side of the machinists square that I am using to mark reference points. To locate the runner wall scribe mark on the throttle body flange face, I must measure this distance and use the existing sharpie marker edge to mark the runner wall location.
Once that is done, use the sharpie to mark the second reference point. You will wind up with two sharpie markers that represent the thickness of the wall that can be ported. I suggest you port the wall to within 1/32” to 1/16” of breaking into the bolt hole depending on whether the intake will see any boost pressure. I would do one side at a time. Measurements must be taken during porting to check how much wall thickness remains. One easy way is to use the machinists square in the runner against the wall and place new scribe marks on the flange face. These scribe marks will move to the right on the flange face. Keep track of how far they are moving from the starting inner wall reference scribe point. When they are 1/16” short of being the width between the original two sharpie marks, you are at your stopping point. Now, clean the flange face by sanding with fine sandpaper and do the left side of the runner the same way.
When you are finished, you will have added ~30+% area for air flow to flow straight through the throttle body runner. Below are two pictures, one of the stock runner on the left and one that has been ported on the right. NOTE the top of the runner walls where they tilt in to the runner. You must be careful not to get too aggressive here as that is the reliefs where the bolt heads rest next to the runner – see the first page intake overhead photo again. Best not to try and take much material out of this area, it’s not needed for good total flow anyway.
For those of you who have the tools, skills and time, you might want to shorten your upper intake. It will reduce the restriction of the stock upper intake length and I have seen it produce 12HP gain over a ported stock upper. You’ll need a good wide band cut-off saw that will be used to cut about 1.75” out of the runners. Be sure the intake is square in the band saw clamps and cut a section of runner out that is just before the vacuum tubes and just before the plenum – look at the picture below. In the picture below, the section that has been cut out is behind the two sections that will be used. Since the runners have taper in this area, the runners will not match when the plenum section is placed up against the front section. The throttle body runner will have a small mismatch too. Use the removed 1.75” section as a template to mark the difference in the runners. Turn it around 180 degrees from the way it was cut, place it up against the front section and you will see the front section is smaller. Use an awl tip or fine marking pen to reach into the reversed section and mark where the front section runners and TB runner has to be ported to match up to the plenum. Remove the cut out section and port the front to match. Also, remove the vacuum tube on the firewall side and drill/tap it for a 3/8” NPT plug so the stock vacuum tree can be used.
While your cutting with the band saw, you’ll also want to shave off the hump just behind the top plate so that the cover plate will sit flat (see blow picture). Use the piece of aluminum you shave off to trim to size and slip into the hole left from removal by inserting it into the top of the TB runner from inside the TB runner. Weld it into place to close the hole. You can also see the two halves set together from the top view.
Below is a bottom view
Here is a side view
You can see the 1.75” freeze plugs in the upper have been pressed out. Use that as a view port to check runner alignment from porting the front section. Also look down the TB runner to check alignment too.
Now, take a carbide bit and bevel the edges of both pieces in preparation for welding. Bevel no deeper than half the thickness of the runner wall.
Once you have verified that all the runners are port matched well and your welding bevels are cut, set the two halves up in a bar clamp or other device to hold the two halves in proper alignment and tack the pieces together. Now, stitch weld the two halves together to avoid warping.
Now, use your porting burs to remove the welds that are above the intake casting and use body filler to fill any small cavities from welding. This is body work plane and simple. place the top cover in place and screw into the two front holes for proper position. Mark the two rear holes for drilling and tapping. Drill and tap them.
When you are done, paint the intake and clear it and it will look very much like the stock intake, just shorter. If you do a good job on the weld removal and body filler you will not be able to see it was welded.
