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Old 06-14-2022, 01:34 PM   #1
cjperformance
 
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LT1 vs LT4 catalytic converter differences?

Anyone know what the differences are in the catalytic converters for LT1 vs LT4? They are different GM part numbers, but they don't hardly give any data online.

I'm really trying to figure out some legal routes to better exhaust. I don't really want to run long tubes (inspections), and the cat converter restriction is (from what I understand) mainly around necked down connection pipe... not the grid itself. At least not as much... I thought about some GESI converters as they are supposedly legal... maybe???, and guarantee no CEL, but would need to find or fabricate my own connection pipes between them and the stock headers/manifold.

I don't have a ton of data on wither the GESI converters improve anything either.

Kooks Green Cats are supposedly EPA compliant too, but dont guarantee that CEL wont light.

I don't want to disable cat codes either. Looking for 100% legal options.
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Old 06-14-2022, 05:32 PM   #2
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I do not know the difference, if any. However, any gain from switching cats to improve exhaust flow, without LTs, is sure to be negligible and a poor benefit per dollar modification. Eliminating cats typically nets 6-8 HP at most, so switching between cats is not likely to get you even that. Also, today’s cats flow quite well for stock and moderately modded engines. I’d put my hard earned $$$ elsewhere.
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Old 06-14-2022, 06:02 PM   #3
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Quote:
Originally Posted by SJFGTO View Post
I do not know the difference, if any. However, any gain from switching cats to improve exhaust flow, without LTs, is sure to be negligible and a poor benefit per dollar modification. Eliminating cats typically nets 6-8 HP at most, so switching between cats is not likely to get you even that. Also, today’s cats flow quite well for stock and moderately modded engines. I’d put my hard earned $$$ elsewhere.
Is that loss for one cat or for both?
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Old 06-15-2022, 06:07 AM   #4
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Both. LOL! I have personally seen at least a half a dozen before and after dyno runs before/after cat removal. Never saw a gain more than 8, saw a couple of 2 or 3 HP gains. Converter switching for exhaust flow or sound on an otherwise stock or mildly modded car is a very poor investment.
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Old 06-15-2022, 07:11 AM   #5
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Ok sounds good. For clarity, I meant primary and secondary. Not one bank
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Old 06-15-2022, 08:11 AM   #6
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Quote:
Originally Posted by SJFGTO View Post
Both. LOL! I have personally seen at least a half a dozen before and after dyno runs before/after cat removal. Never saw a gain more than 8, saw a couple of 2 or 3 HP gains. Converter switching for exhaust flow or sound on an otherwise stock or mildly modded car is a very poor investment.
Were those all naturally aspirated bolt on cars? From my understanding, the power gains on cat removals are much higher than what you indicated in forced induction applications.
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Old 06-15-2022, 10:16 AM   #7
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In addition to any possible performance increases, I have been told several times that forced induction will eventually destroy the stock LT1 cats... which is why I was wondering if the LT4 cats are any different... either in flow characteristics, or in construction.

So at some point I'll have to replace them anyway... May as well be prepared with a good replacement strategy.
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Old 06-15-2022, 11:37 AM   #8
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Just get headers and GESI Gen 2 cats. They are handling 1000hp + and not failing.
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Old 06-15-2022, 01:20 PM   #9
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Just get headers and GESI Gen 2 cats. They are handling 1000hp + and not failing.
Thank you for the input. This is the route I am leaning towards. I will probably hold out if/until my stock cats get trashed due to cost investment.
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Old 06-15-2022, 06:23 PM   #10
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Quote:
Originally Posted by cjperformance View Post
I have been told several times that forced induction will eventually destroy the stock LT1 cats...
While this is true, the bigger problem is the restriction they cause will eventually give you soaring cat temps and an inefficient motor as you approach 650-700 WHP. The way the stock LT1 cats neck down where they meet the exhaust manifold is crazy small.

Quote:
Originally Posted by KingLT1 View Post
Just get headers and GESI Gen 2 cats. They are handling 1000hp + and not failing.
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Old 06-15-2022, 06:53 PM   #11
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Right. Its prob less than 2 inch section... then i went and crammed an o2 sensor in there too.
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Old 06-16-2022, 10:24 PM   #12
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I can't find anyone selling or in stock with the GESI cats anywhere, I know someone posted a link to a place I think that was selling them a while ago but I can't find it.

I have completely stock exhaust now minus the AFM valve delete (I deleted them in an attempt to stop the rattle and this was before the grind of the ear NPP rattle fix) and I want to put in GESI cats in the primary location and remove the secondary ones. I think the primary do the majority of the unburn hydrocarbon cleanup so they do most for the bad smells and I think the secondaries are more for Nox.

The thing I am trying to figure out is how I want to do it. The secondary cats have an offset input/output, which is going to make it look weird and akward with a relatively tight s bend pipe in their place, I think I might just try to take out most of the section up until the bend.
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