Plenum, 60mm Throttle Body, and Throttle Linkage Bracket

Update October 9, 2005:

When I first performed the 60mm modification I went through it quickly and took some shortcuts. Recently I performed the modification for a second vehicle with more attention to aesthetics. The first two pictures show the results of my latest effort.

Throttle Linkage Bracket

Performing the 60mm throttle body modification

The following are the step-by-step details of modifying the plenum to accept the 60mm TB. The steps include refined methods learned from the second time I performed the modification. The photos, however, are from the original modification.

If you do the math (area of a circle = pi x radius squared) the 60mm throttle body is 33% larger than a 52mm and a whopping 70% bigger than a 46mm. The picture below is a 52mm TB viewed through a 60mm TB

The Jeep 4.0 H.O. throttle body necks down to approximately 52 millimeters on the intake side of the throttle plate. The first step is to bore out the necked-down part of the TB to make it 60mm all the way through. Remove the throttle plate and throttle shaft. I used a 2-inch-diameter sanding drum to bore the throttle body. I used 80 grit to remove 90% of the material until the necked-down portion of the TB was almost the same inside diameter as the front portion of the TB. More material will be removed later when the throttle body is bolted to the plenum. I used a drill press to bore the TB the first time around. The second time I used a hand drill and it worked very well.

The next step is to drill mounting holes to match the 3.0-plenum studs. Your stock TB can be used to mark the spots where the holes will be drilled.

Cover the areas shown in the pictures below with JB Weld and let cure for 15 hours. Surfaces should be cleaned with acetone before applying JB Weld. Use liberal amounts of JB Weld on the bottom of the plenum. This is the area where the biggest hole will be. After the JB Weld is fully cured slide the throttle body over the mounting studs of the plenum. Mark a line on the plenum flange along the inside diameter of the throttle body with a scribe or sharp knife. Open up the plenum to 90% of the diameter of the scribed circle using an 80-grit 2-inch sanding drum on a hand drill. Bolt the throttle body to the plenum and finish up the remaining 10% of the sanding with a 120-grit 2-inch sanding drum. The inside of the TB and plenum can be polished further with finer grit sand paper such as 220. For a highly polished look follow the 220 grit with 320 then 400 then steel wool.

Remove the stock TB mounting studs from the plenum. Use 8mm x 20mm hex head bolts to mount the TB to the plenum.

The Jeep TB throttle plate rotates in the opposite direction of the stock 3.0 TB so the throttle linkage needs to be modified. I removed the throttle cable lever from a 46mm 3.0 TB. I flipped it over and welded it to the Jeep throttle cable lever. The arrows show where the two throttle levers are welded together. In the second picture you can see the nut, which holds the Jeep throttle lever in place through the hole in the 52mm throttle lever. These two holes should line up to keep the lever on the same axis.

The stock throttle cable holder was turned upside-down and welded to a bracket fabricated from angle iron. The throttle cable bracket bolts to the plenum and cylinder head.

Because the Jeep TB rotates in the opposite direction of the stock TB the outside two wires of the throttle position sensor female connector must be swapped. Remove the rubber seal from the back of the connector. Use a pocketknife to pry and remove the green plastic piece. The terminals can now be removed if a sharp object is used to bend back the little plastic things that lock the terminals in place. Swap the outside two terminals. Replace the rubber seal and green plastic piece.

There is a plastic rib inside the throttle position sensor male connector, which needs to be removed in order for the two connectors to mate properly. The rib can be removed using a sharp knife. The rib has already been removed in this picture.

Plug in the throttle position sensor and idle air control and you’re ready to rock.

For more info, contact Jim Seko at jimseko@yahoo.com