High Flow CAT Install

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Apr 6, 2026 | 09:28 PM

mcervinojr

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Heel & Toe

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High Flow CAT Install

Bought a set of Milltek's from a forum member on here.

I have a shop that's going to do the install for me, but I hear that best practice is to use new GM gaskets / flanges. Does anyone have quantities and part numbers on what I'll need?

Appreciate the help!

Apr 7, 2026 | 12:17 AM

stargtsi

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Joined: Jul 2023

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From: Colorado

X3 2319420. The other donut one is reusable.

Apr 7, 2026 | 10:10 AM

jaedymack

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you are going to want the O2 simulator "mini cats" too so you don't throw an engine light. I got mine from Big Daddy Garage. I have had my high flow cats on for over a month and no lights. My car sounds great.

Apr 7, 2026 | 10:27 AM

mcervinojr

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Did you do the mini CAT only or the Mini CAT w/ Angled CEL combo?

Quote:

Originally Posted by jaedymack

Apr 7, 2026 | 02:56 PM

JohnStuttle

Do Not Quench The Spirit

Joined: May 2005

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From: Fishers IN

St. Jude Donor '13,'19 thru '26

Quote:

Originally Posted by jaedymack

With what he said! I have had mine on for about a year now and no CEL!

Mini Cat O2 Sensor CEL FIX

Last edited by JohnStuttle; Apr 7, 2026 at 03:29 PM.

Apr 7, 2026 | 04:01 PM

mcervinojr

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Quote:

Originally Posted by JohnStuttle

With what he said! I have had mine on for about a year now and no CEL!

Mini Cat O2 Sensor CEL FIX

Does this work with aftermarket intakes?

Apr 8, 2026 | 08:44 AM

jaedymack

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I did the mini cat with angled CEL Combo. Not sure on aftermarket intake. I do have the AFE air filter and no engine lights.

Apr 9, 2026 | 09:05 AM

ZORANGE

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Joined: Oct 2024

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From: Old Dominion

Quote:

Originally Posted by JohnStuttle

With what he said! I have had mine on for about a year now and no CEL!

Mini Cat O2 Sensor CEL FIX

I also have the high-flow CORSA cats but did not need the "mini cats" as you call them. I did consider getting them from Big Daddy, however.

My non-Z51 also has the Afe dry filter. No CELs since installing the Corsa cats 4k miles ago.

Last edited by ZORANGE; Apr 9, 2026 at 09:14 AM.