To gut or not to gut that is the question?

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1998SSLT

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Greetings to all! I'm new to this site wish I had found it years ago. Just put new 5.7 HD engine in my 98 Sierra. Added Taylor Cable manifold spacer and Gibson shorty headers along with CFM Tech throttle body. My question is should I gut the catalytic converters or will it become a gas guzzler? Also will there be any significant improvements made? Thanks for your time.
 

df2x4

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Fuel consumption won't change any. You won't notice any improvements. The only things you will notice are a constant check engine light until you get the rear O2 sensors tuned out of the PCM, and a constant smell of gas due to the lack of the catalyst. If I were you I'd leave them intact.

Side note, welcome to the site from another Missourian!
 

Elroy

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my old cats were not flowing well, replaced with magnaflow SS cats and system ($$$$) and it is a night and day difference, maybe if your 20 yr old cats are in like new condition you wouldnt see much improvement but replacing the cats on mine was a huge improvement
 

df2x4

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X2 on that ^. I also replaced the cat on my red truck with a Magnaflow Y-pipe/cat assembly and I'm very happy with it.

In short I would not remove the cats if I were you, but I would replace them if you suspect that they're clogging up.
 

1998SSLT

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I'm told they're in good shape (always burn ethanol free premium) but I'm sure they don't flow as new. I've already spent more than I planned or wanted to, of course. Thought maybe leaving them on but hollowed out may work similar to high flow cats and save me some $$$. Thanks for the replies, as well as the welcome.
 

MarkZ28

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Wont hurt anything, leave them off or gutted. Install anti foulers between the second O2 sensors and bungs on pipe. Thst will fool the computer. All the secondary sensors do is confirm that the cats are working within a certain range. Will not affect anything else. The newer trucks like yours have a monolith style material, not that crappy pellet kind that do restrict flow. Stock you wont notice much difference in power on your truck, but if you add cubic inches, bigger port heads, good cam, bigger TBI/carb/injection throttle body, it will be noticeable.
 

Urambo Tauro

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Aren't OE cats already "high-flow"? I thought that "low-flow" OE cats were a thing of the past, found mainly in older, early emissions systems. Just like how all cars are built with literal cold air intakes nowadays, and there's almost no point in getting an aftermarket "cold air intake".
 

big_mike

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I got a set of 2.5" hiflo cats pretty cheap, like around $100 shipped. I'd never pay the price to replace with direct fit replacements, way overpriced.
 
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