fltechpilot

Currently trying to fit a Borla cat back system onto an 84 US car. There is a flange coming off the cat that has a larger outside diameter than the inside diameter of the borla pipe.

Has anyone run into this?

Really trying to avoid altering the cat as it is less than a year old.

Jerry Feather

I run into that every time I try to match the same size pipe or tubing--the outside diameter of one is always bigger than the inside diameter of the other one.

fltechpilot

I've never heard of people running into this issue when installing a Borla system. My cat is 928 part number and not some knock off brand. I'm assuming that if everyone had to cut that flange off the cat, I would have read about it. Wondering if there's a simpler solution that I'm missing.

Jerry Feather

Why don't you swage the inside of the pipe that needs to fit over the flange at the outlet.

Jadz928

Is the part sticking out from the flange a separate piece? Usually there is a sealing ring btw the cat and intermediate.
Hard to tell from the pic...

fltechpilot

The original sealing ring was located around the outside of that flange and was removed. The flange in the picture is a part of the cat itself.

Fsharp9

Jerry Feather

What does the Cat flange bolt to? Show a picture of the front end of the Borla pipe.

fltechpilot

The Borla is currently loosely fit on the car. It has the same 4 bolt mating surface as the stock exhaust, except it is completely flat and not beveled like the stock exhaust to accept that piece of the cat.

fltechpilot

When installing the Borla system, it is a known issue that you cannot reuse the sealing ring. There is a 964 exhaust gasket that is used in its replacement. After thinking about this last night, my plan is to use a sawzall to cut that extension off the cat. Even if I ever wanted to go back to the stock exhaust system, I could still seal it with the 964 gasket.

Jerry Feather

Why cut it off? Why not just grind it down in outside diameter so it will fit into the recess in the Borla flange.

Edit: Oh, I get it. This is not a picture of the Borla flange.

Imo000

Needs more muffler cement!!

fltechpilot

Cutting that extension off the cat did the trick. Didn't want to cut it, but it's all sealed up and good to go