Kooks green cats

[engineermike]

I’d be really interested to see how HJS cats hold up to supercharged v8 applications. It looks like most that run them are na or turbo. Turbos are much easier on cats. Myself, I’ve recently swapped to gt500 cats because they are still ceramic and the material thickness appears to be double that of a GT.

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[Zelek]

Which brand spacers did you add?

Big Daddies L-shaped ones. The mini cat spacers will work too.

 

[22Coyoti]

I’ve researched and tested the issue more than any sane person should. My conclusion, right or wrong, is that stock cats that use ceramic substrate usually fail due to thermal shock. Many aftermarket FI tunes run lean with low timing at wot and low rpm, which is a recipe for thermal shock. Add to that, cool-down periods before dyno pulls and drag runs and you made it worse. Every failed stock cat I’ve seen has a cracked monolith, which is evidence of uneven heating not overtemp. Conversely, the metal substrate aftermarket cats fail from high sustained temps or inadequate mechanical attachment of the spiral. I believe these CAN be pretty good but not all are. Even with the best attachment they still can’t sustain the temps as well as ceramic. The yield strength of 304 goes down to basically nothing at 16-1700 deg f.

Hey,

Planning on doing a whipple stage 2 kit with the whipple tune on my stock 2022 automatic mustang aswell the oil pump gears. I want to keep the stock cats on the car. Will I be safe to do so because I am using the whipple tune?

 

[22Coyoti]

I’d be really interested to see how HJS cats hold up to supercharged v8 applications. It looks like most that run them are na or turbo. Turbos are much easier on cats. Myself, I’ve recently swapped to gt500 cats because they are still ceramic and the material thickness appears to be double that of a GT.

Also how did the gt500 cats fit? And where did you buy them from?

 

[engineermike]

Hey,

Planning on doing a whipple stage 2 kit with the whipple tune on my stock 2022 automatic mustang aswell the oil pump gears. I want to keep the stock cats on the car. Will I be safe to do so because I am using the whipple tune?

They will most likely fail at some point, depending on your driving style.

 

[engineermike]

Also how did the gt500 cats fit? And where did you buy them from?

I bought them used.

The gt500 cats require cutting and welding to make them fit. I can detail this if you need.

 

[22Coyoti]

Yes please if you don’t mind. I’m going to look for a pair

 

[engineermike]

Passengers side: At the front it will bolt to the header but it’s too tight to the floor plan. A 1/2” spacer is needed to get some clearance. At the rear, it’s 2.75” diameter where the stock gt is 2.25” at the slip fit, so this will need to be swaged down or the resonator upgraded.

Drivers side: At the front, the stock gt manifold does not have a flange. It will need to be cut between the collector and cat and a 2-bolt flange welded to the stock manifold to adapt to the gt500 cat. At the rear, it’s the same size change as the PS.

Edit: On the drivers side, a gen1 manifold has a 2-bolt flange but it’s clocked wrong. If I did it again I would probably try it with a gen1 manifold and custom 2-bolt clocked adapter.

 

[22Coyoti]

Passengers side: At the front it will bolt to the header but it’s too tight to the floor plan. A 1/2” spacer is needed to get some clearance. At the rear, it’s 2.75” diameter where the stock gt is 2.25” at the slip fit, so this will need to be swaged down or the resonator upgraded.

Drivers side: At the front, the stock gt manifold does not have a flange. It will need to be cut between the collector and cat and a 2-bolt flange welded to the stock manifold to adapt to the gt500 cat. At the rear, it’s the same size change as the PS.

Edit: On the drivers side, a gen1 manifold has a 2-bolt flange but it’s clocked wrong. If I did it again I would probably try it with a gen1 manifold and custom 2-bolt clocked adapter.

Having a hard time finding gt500 cats used and dealer wants like crazy amount of money for them. Would a high flow cat be better than stock cats, hearing mixed things about them being worse or better?? Also do you know if the high flow cat fit on the stock headers? For example if I purchase a kooks green cat will I also need headers. I really don’t want to get rid of them and I’m never planning on pushing over 700 whp on 93 and on whipple tune

 

[engineermike]

…Would a high flow cat be better than stock cats, hearing mixed things about them being worse or better??

I don’t think anyone can answer this with certainty.

Also do you know if the high flow cat fit on the stock headers?

They can be welded to the stock headers.

 

[22Coyoti]

I don’t think anyone can answer this with certainty.



They can be welded to the stock headers.

thank you Much appreciated

 

[JoeCee]

Will the highest grade Gesi cats bolt up to the stock manifolds? Need a solution for a low boost gen 3 setup.

 

[engineermike]

No, no cats will bolt up to any gen2-gen3+ coyote drivers side ever.

 

[JoeCee]

No, no cats will bolt up to any gen2-gen3+ coyote drivers side ever.

What do you recommend then for a low boost application? Are headers a must?

 

[engineermike]

What do you recommend then for a low boost application? Are headers a must?

If you want to prioritize cat longevity over performance I think I’d run stock cats with 8 psi or less, 19-20 deg timing, and super rich at wot like .72-.73. Have cot drop it to around .68 if it will do it without misfires.

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