Help me understand high flow cats on FI

[RTR077]

I keep reading that FI can negatively effect cats, even high flow cats. Most people say to take them out altogether.

What I don't understand is that other platforms use cats without any 'obvious' issues:

- Saleen/Roush/Shelby S/C Mustangs - you can throw in F150s for that matter
- GT500
- Other high powered cars

If they are fine using cats, or high flow cats, why would it be a concern for a S/C GT?

I am currently running stock cats and will need to keep them on for NC inspections. Would like to fit aftermarket headers, but I am confused af what to choose. Keep OEM? aftermarket or high flow aftermarket

Driving: spirited and the occasional track.

Thanks.
James

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[ProChargerTECH]

I have NEVER seen a set of "high flow" aftermarket cats, last longer than an OEM unit in a high HP forced induction situation. (This is based on my 20 years of tuning high HP cars with FI) I also don't sell or install items like that, so I have no reason to sugar coat that. (Since there's no profit coming from sales of such items).

High HP Shelby F150's (like you mentioned, do fail cats)

GT500's have cats designed for high HP FI from the start
Hellcats and other cars like that, same as above.

The issue with cats, is the same as OEM engines. A stock coyote engine, is NOT a GT500 engine... same as a 6.4L HEMI, is NOT the same as a Hellcat engine. (Same goes for cats)

 

[stannypack]

so when I eventually whipple my gt but have yearly emissions testing, what's the best solution? would high flow cats even pass emissions?

 

[SheepDog]

so when I eventually whipple my gt but have yearly emissions testing, what's the best solution? would high flow cats even pass emissions?

https://shop.2mfabrication.com/product/2015-2020-mustang-gt-performance-pipes-cat-deletes

Install this. This way, you can easily install the OEM cats for inspection/emissions, but run catless the rest of the year.

Your other option is to go with the Gen2 GESi cats, either with long tubes or the Mak pipes
If you don't want to do headers.

https://www.makperformance.com/2015-2023-Mustang-GT-MAK-Performance-Pipes_p_299.html

 

[engineermike]

I think we can all agree that the Roush phase 2 gen3 gt is a very safe and high quality setup. Those things still fail cats quite often. They run very rich on the Roush cal and cat overtemp is active, yet they still fail. The stock gt cat monolith is a very high cell count (750 cspi?) and very thin material so thermal shock causes cracks very easily.

 

[ProChargerTECH]

so when I eventually whipple my gt but have yearly emissions testing, what's the best solution? would high flow cats even pass emissions?

Define "pass emissions"

If you are just talking about a sniffer test or a "green lights are on, go" ... maybe.

Full blown legit emissions test, involving a CARB sticker... highly doubtful.

 

[SpeedLu]

My stock cats burned up within three months of installing my supercharger. I put on some aftermarket high flows w/headers and I've been running them for two years now without issue.

 

[stannypack]

Define "pass emissions"

If you are just talking about a sniffer test or a "green lights are on, go" ... maybe.

Full blown legit emissions test, involving a CARB sticker... highly doubtful.

I meant full on emissions like virginia or cali lol, but looks like you could just bolt on/off your legit cats come emissions time?

 

[SheepDog]

I meant full on emissions like virginia or cali lol, but looks like you could just bolt on/off your legit cats come emissions time?

The Driver side cat is part of the manifold, which is far from easy to swap. This is why the Mak and 2M fabrication options require you to cut the cat off, and then weld a flange onto the pipe and manifold

 

[engineermike]

The Passenger side cat is part of the manifold, which is far from easy to swap. This is why the Mak and 2M fabrication options require you to cut the cat off, and then weld a flange onto the pipe and manifold

The driver's side is the manifold-cat combo. It isn't hard to swap out though. It just makes it hard to come up with "alternatives".

 

[stang17]

I had my whipple installed by dealer and wrapped into financing. Stock cats and whipple tune made it barely a year and a few thousand miles before cats started to fail.
I replaced with Kooks 1 7/8 headers with their regular high flow cats. Those cats failed even quicker than stock ones running same whipple tune within 700 miles.

As previously stated, our cars OEM cats are not designed for boost. GT500s, Hellcats, and other OEM boosted vehicles have cats designed for that and most are GESI brand.

Kooks offers "green" catted connection pipes which are just rebranded GESI cats. These cats can withstand boost and GESI offers options to support up to 1200 HP per cylinder bank.

Hypothetically someone can have hollowed out cats for visual inspection and a set of green catted connection pipes to swap in/out on testing days.

 

[ProChargerTECH]

I had my whipple installed by dealer and wrapped into financing. Stock cats and whipple tune made it barely a year and a few thousand miles before cats started to fail.
I replaced with Kooks 1 7/8 headers with their regular high flow cats. Those cats failed even quicker than stock ones running same whipple tune within 700 miles.

This has been my experience.

It does depend on how a customer "treats" their car... so some get a LOT of miles out of them.

That being said, I have made 1,205 whp through stock Z06 cats and they have lived a decent long life, after being turned down to about 900hp. Which was great to see, but again thats a cat that was designed for F/I from the factory.

 

[NJMike]

I have 1 7/8" Kooks with green cats on my Mach 1, but only a few hundred miles so far. BUT I also have 2" Kooks with green cats on my Trackhawk for 3 years now and no problems at all.

 

[ProChargerTECH]

I have 1 7/8" Kooks with green cats on my Mach 1, but only a few hundred miles so far. BUT I also have 2" Kooks with green cats on my Trackhawk for 3 years now and no problems at all.

I have nothing to add, other than..... I want your EXACT car.

 

[NJMike]

I have nothing to add, other than..... I want your EXACT car.

$$$$$$
Which one

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