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Delete Cat question

GaBnn3

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Greetings all! I am not a trained mechanic and only feel comfortable fixing what is explained in the manual and/or on Youtube. But, my best source of info is this forum. Typically my repairs are to stock specs because that's what's in the manual. But my exhaust rotted away. The cat is the only part still good and in place. Emissions compliance is not required of me here in Ma. I'm considering cutting off the cat and running a straight pipe from the y-pipe to the muffler. I did a quick web search on the wisdom of such and it seems there may be a benefit in so doing. I'd like to know if the experts here can advise if it is a good idea. I hope to avoid a situation where I will have regrets. The engine is the 5.7L. Thanks.
 

dyeager535

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Is it the old OEM "pancake" converter?

Those were, in fact, bad for performance.

I'll second the "put a high flow cat on" thought however, especially if this is a K5 and you run with the rear window down. Even with a well running setup, you will get noxious fumes at times entering the cab that way, a converter does a really good job of mitigating that.
 

K85 Octane

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Agree
Any place not CA will have cats cheap enough to replace. They help and don’t negatively affect the car enough to go without.
 

HankScorpio

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I was running without cat, no performance increase from a seat of the pants feeling. Doing a new exhaust because of an engine swap, I will be putting a cat on this time. The exhaust was pretty nasty when it would blow in through the back window, hopefully the cat will help with this. On a pickup you would probably never notice.
 

sweetk30

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i had a 350 tbi that had a few year old replacement pancake cat from the dealer before i got it . then i removed it and also did a 40 series flow master with single in 2 tail pipe out and WOW what a huge jump in the driver seat on power .

for the people who didnt notice any then you must of had a dead or empty pancake cat before you removed it .

as said tho if any thing go newer honeycomb style cat and keep the stink WAY down . i am to the point on my k30 i want to add one .
 

Bent77

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I like the Magnaflow cats. They’re not very expensive, smaller case. Been known to run cat only, no muffler
 

dyeager535

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I'll be going magnaflow when I finally get around to redoing the exhaust, as they gave me solid numbers when I asked.

Fwiw, if you do decide to run a cat, magnaflow says 250-350F on the inlet pipe (not converter body) is what they generally see where placement of the converter will be correct. Pretty easy to determine where that is using a tempilstik "crayon" on the existing pipe.
 

Barry Ingram

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In my experience eliminating the cat provides minimal power gains unless you have lots of cubic inch & good flowing heads , intake.

May cause emission inspection failure depending on local regulations.
 

Wes Harden

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One thing if you do keep your cat/a cat the other emission equipment needs to be there and function. a fuel rich running engine will eventually damage the cat. Most likely melt it and degrade seat of the pants felt performance.
 

mpg7_400

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Greetings all! I am not a trained mechanic and only feel comfortable fixing what is explained in the manual and/or on Youtube. But, my best source of info is this forum. Typically my repairs are to stock specs because that's what's in the manual. But my exhaust rotted away. The cat is the only part still good and in place. Emissions compliance is not required of me here in Ma. I'm considering cutting off the cat and running a straight pipe from the y-pipe to the muffler. I did a quick web search on the wisdom of such and it seems there may be a benefit in so doing. I'd like to know if the experts here can advise if it is a good idea. I hope to avoid a situation where I will have regrets. The engine is the 5.7L. Thanks.
Depends on the vehicle year. Computer or no computer? Fuel injected or carb?
 
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