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Cat Removal-How Did You Do It?


Arrest Me Red

I've heard that cat removal is the way to immediate large performance gains. Do those who have done that agree? Looking the job over, I see two options. Cut the cats out, preserving the welded Y and the flanges to the turbos, and fit and weld tubing in between the stubs. The second option preserves the factory assembly by removing the flanges and Y-pipe assembly and replacing with new flanges and custom pipe assembly.

I suppose the cats can be welded back in later if it became necessary to restore originality. It seems the easier approach. How did you do it?
I completely agree you will see a major power gain. You will also have happier cooler running turbos. Just the reduced back pressure alone will spool your turbos much faster and create increased peak boost. You will need to watch your boost gauge carefully after the mod to make sure you are not going over 56-58" depending on the quality of your gas. If you are you will need to adjust the waste gates to back it down.

I see you have a 1990 also. Mine had some exhaust mods before I got it so I don't know how it looked stock. You mention cats so I assume you have pre-cats in the front Y-pipe? Mine does not have them but does have something very similar to the modification you describe. There are 2.5" pipes coming off the turbos that bolt with flanges into a short Y-pipe that exits into a single 3" pipe also flanged. This 3" pipe has a removable center section where I can bolt in either a 3" high flow cat or a 3" test pipe. This swap takes about 15 minutes and the car will pass emissions with flying colors.

Do you have a center main cat or just these cats in the Y-pipe? I think the single high flow cat that bolts in and out is a nice way to go.
Cat Removal

I have two cats in the front Y. They look like a standard L-98 factory cat with weld ends. I also have the 3" straight pipe aft of that, where the single cat would normally be on the L-98. The front Y slips into the 3". I haven't measured the length to see if a standard cat will fit without modification. Do you have flanges at the turbos and to the Y-pipe, and at the Y into and out of the 3"?

I normally use 93 octane pump gas. Would be concerned about how to dial in the waste gates to the right point so that I know with confidence that I won't detonate on the dyno. Just keep the boost gage below 56"?

Still looking for additional available advice on the simplest way to do this.
Re: Cat Removal

Arrest Me Red said:
Do you have flanges at the turbos and to the Y-pipe, and at the Y into and out of the 3"?

If I understand the question correctly, yes. I'm assuming your forward Y-pipe is 2.5" OD. So my suggestion is to cut the pipe ahead of the Y and weld on two bolt flanges. Then have 2.5" pipes fabricated from those forward to the turbos. Intall flanges on the back side of those pipes to bolt to the Y. Cut the back side of the Y where the 3" slips in currently. Measure up a high flow Random Technologies 3" cat for length. (If you never plan to use it except for emissions tests you could go with any 3" cat.) It should have 3 bolt flanges on each end if you get the right one. Then put flanges on the front and back side of the existing 3" pipe at the proper location. Either use the section of 3" pipe removed and install flanges to make a test pipe or just use new pipe. You will then have a single main cat that can be easily bolted and unbolted.

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