High flow cat options?
Supporting Vendor
Joined: May 2018
Posts: 5,250
Likes: 416
From: Philadelphia
Give me a shout, happy to help
- Alec
267.788.4897
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Alec @ Forza Motor Works
(267) 788.4897 Call/Text
info@forzamotorworks.com
www.forzamotorworks.com
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Alec @ Forza Motor Works
(267) 788.4897 Call/Text
info@forzamotorworks.com
www.forzamotorworks.com
Your trusted source for premium parts - offering competitive pricing, exceptional service, and professional installation options.
Corsa | Borla | AWE Tuning | Girodisc | Halltech | American Racing Headers | Milltek | Soler | Weld | Fabspeed | SOUL | Kooks | BC Forged & 100's more!
Advanced
Joined: Nov 2025
Posts: 65
Likes: 80
AWE built some wicked stuff. I'm right up the road in Ottsville. Can you PM me the install price for the the High Flows when you get a chance? I know what you're asking for the Millteks.
Instructor
Joined: Dec 2023
Posts: 228
Likes: 143
From: Long Island
Supporting Vendor
Joined: Jan 2016
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From: Orange County, CA
Racer
Joined: Jan 2025
Posts: 392
Likes: 178
From: North Carolina
Real world answer is that it depends on the dealer doing warranty work.
Theoretically, GM would need to identify the modification as a causal factor for the associated breakdown. Some draw a harder line, and some are not so stringent.
I have had warranty work done on a hellcat that was straight pipe, on e85, pulleyed down and even on an Evo that had upgraded 3076 turbo, tuned, Shephard transmission, etc.
I have never had a warranty claim rejected by any manufacturer, but have heard horror stories of those who have.
I modify under the assumption that is something were to break in the area (1 level up and 1 level down from modification point), then i am prepared to pay for the repair (lilely aftermarket upgrade).
The only deviation from this would be tuning of the ECU, which i understand not to be currently possible for our platform, but could potentially void any and everything powertrain and certain things electrical
Theoretically, GM would need to identify the modification as a causal factor for the associated breakdown. Some draw a harder line, and some are not so stringent.
I have had warranty work done on a hellcat that was straight pipe, on e85, pulleyed down and even on an Evo that had upgraded 3076 turbo, tuned, Shephard transmission, etc.
I have never had a warranty claim rejected by any manufacturer, but have heard horror stories of those who have.
I modify under the assumption that is something were to break in the area (1 level up and 1 level down from modification point), then i am prepared to pay for the repair (lilely aftermarket upgrade).
The only deviation from this would be tuning of the ECU, which i understand not to be currently possible for our platform, but could potentially void any and everything powertrain and certain things electrical
Supporting Vendor
Joined: Jan 2016
Posts: 82,505
Likes: 718
From: Orange County, CA
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Advanced
Joined: Nov 2025
Posts: 65
Likes: 80
I would imagine if a cat melted down and the motor popped, you're on the hook. That would be highly unlikely on the factory tune unless someone added FI or was playing with NOS, or using a fuel that isn't CC friendly. But it is possible and a consideration.
Heel & Toe
Joined: Aug 2024
Posts: 23
Likes: 22
I replied earlier in the thread saying I have Milltek high flow cats and no CEL. That reply was clearly a jinx, I popped a check engine light today. Scanned using my reader and had no code but the light was on, so maybe a prelim not a hard code but not sure. The light came on during a warm start with about 35 degree Fahrenheit ambient air temps. I’ve had the cats on about 125-150 miles. I don’t know my current software version.
Instructor
Joined: Dec 2023
Posts: 228
Likes: 143
From: Long Island
@Malfred Thanks for sharing - Were you able to clear the CEL and if so, did it pop back on again? I would hate having to deal with that...
Cat back exhaust better in terms of CEL possibilities?
Cat back exhaust better in terms of CEL possibilities?
Thread Starter
Burning Brakes
Joined: Oct 2019
Posts: 843
Likes: 526
From: Colorado Springs
If an aftermarket cat’s substrate breaks down, there is a chance that pieces of it could be ingested during a high rpm downshift. For this reason AND I dont want to pay $3k+ for high flow cats, I want to install catless test pipes. Who sells ‘em?
Safety Car
Joined: Mar 1999
Posts: 3,611
Likes: 182
From: Toronto, Canada
Check out this video by Paragon Performance discussing the Milltek cats.
The o2 sensor bung/angle is very sensitive and can trigger a cel. Milltek made a revision after the original design to accommodate the Eventuri (which still wasn't compatible) and customers are reporting a cel. Milltek will now continue to sell the original version which seems to be working without any issues.
I have been using the the original v1 design with the oem airbox and have never had any cel logging over 4K miles.
https://youtu.be/TbYuStRjb8M?si=2SGQ4KOfILIQ5EFt
The o2 sensor bung/angle is very sensitive and can trigger a cel. Milltek made a revision after the original design to accommodate the Eventuri (which still wasn't compatible) and customers are reporting a cel. Milltek will now continue to sell the original version which seems to be working without any issues.
I have been using the the original v1 design with the oem airbox and have never had any cel logging over 4K miles.
https://youtu.be/TbYuStRjb8M?si=2SGQ4KOfILIQ5EFt
Racer
Joined: Mar 2013
Posts: 400
Likes: 112
From: MD
Even if u clear the cell, dealer can still see the ecm log and trust me, when u have to make any engine related warrenty claim, dealer will blame u for ignoring(no service records) all these CELs. I got v1 miltek and cel at 2600miles. Got 02 spacers and no cell since.(fingers crossed btw)
Instructor
Joined: Dec 2018
Posts: 154
Likes: 71
From: Niagara Ontario Canada
CEL update?
Any updates/fix for the increase in CEL with Milltek HFC since the new GM update to the cars?
I was told last week that there has been a GM over the air update, that now recognizes hi flow cats. Any truth to this? Any fixes?
I was planning on ordering some, but trying to avoid the CEL if I can.
Any insight will be appreciated
I was told last week that there has been a GM over the air update, that now recognizes hi flow cats. Any truth to this? Any fixes?
I was planning on ordering some, but trying to avoid the CEL if I can.
Any insight will be appreciated