Porting a Stock Upper Intake

Porting 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 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. NOTEthe 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.