PerformanceTrucks.net Forums - 90mm Radix alterations

I've had numerous people asking me for information, so here goes:

I cut out a paper template using the back of the TB as a guide. I used a SSR 90mm TB, so it has a little different shape than the vette version. This pic shows roughly how the 90mm mates up to the 78mm flange.

http://z71.net/radixtboutline1.jpg

Here is an overview of what needs to happen:
The tube behind the flange is plenty large enough to support a 90mm opening. I removed all three original TB studs from the flange. The lower two holes I reused with longer bolts, the top one doesn't get used. The yellow circle is roughly where I tapped another bolt hole. I colored in the area that I needed to remove with a blue marker (shown outlined in red in this picture). The area shaded green needs to be filled in as the 90mm doesn't have any idle airflow bypass needs. I used a large machine screw and JBWeld for this.

http://z71.net/radixtboutline2.jpg

I used a plain jigsaw with a metal blade to make the main cut. I removed the lower guide from the saw and handled it like a mini sawsall, so I wouldn't be beating up the surface of the flange.

http://z71.net/radixtbcut.jpg

At this point, I used a rotary tool to finish shaping the opening in the flange and to smooth it all out. I have a large flex shaft version of the dremel that works wonders. The plain dremel should work fine too.

http://z71.net/radixtbclean.jpg

Now to the TB itself. The lower two holes are just a bit wide to fit over the 78mm flanges original lower studs. So I took a small round file and elongated the lower holes about 1/4" as shown below. This takes care of 2 holes and also firmly sets the position of the TB in relation to the flange. I created a third hole in the flange as marked in yellow above. That just leaves one hole to be secured.

http://z71.net/radixtb901.jpg

Now from the rear, we can see the 90mm TB leaves one of its bolt holes sticking out past one edge of the stock flange. Instead of making a major alteration to the flange, I chose to use a "J" bolt in the 4th hole. That bolt basically is secured by reaching behind the rear of the flange. I trimmed the extra length off the bolt so it doesn't stick out farther than needed. I made a small depression in the back of the flange with a drill bit for the J bolt. This basically makes a seat for the bolt so it always gets secured in the same location and doesn't move.

http://z71.net/radixtbflange1.jpg

From here you can see the mostly completed 90mm mod from the rear. The J bolt is hidden behind the motor and can't be seen. On the left you can see the rear of the flush mount stud I used for the other top bolt hole. This J bolt is very firmly secured, so don't let that scare you off.

http://z71.net/radixtb6.jpg

Step not shown is filling in the open spot on the flange. I didn't like the idea of filling that whole area in with JBWeld. So I found a large headed machine screw that just fit inside that recess. I tapped the screw and made sure it went just past flush. Now filling in the rest of the thing with JBweld was easier. With the screw taking up most of the space, I didn't have to use as much filler and know the JBWeld has a more secure hold. Physically the JBweld came out gray in color. It stands out more on my polished flange, but would probably match the color of a painted radix pretty well. You can see this area with JBWeld in the picture below, barely sticking out above the top of the TB. I'm completely happy with how well the JBweld part of this worked out.

http://z71.net/radix90.jpg

Why do this mod? It works well, its cheap, you can do it yourself, and its reversible. By adding the top stud back to the flange, you can remount a 78mm TB if you'd like.