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Discussion Starter · #1 ·
i have been thinking about hollowing out my catalytic converter but i am not sure that my check engine light will come on if i do. also, is there such thing as too little back pressure. thanks for the help
 

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it will be loud, if you have a straight through muffler on the ar, i do and it is loud. gives a little more HP
 

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There is such a thing as too little back pressure. You change the resonance of the exhaust by removing the cat element, possibly harming power output. Modern day cats are alot better than the old school pellet type converters. The cats on all new cars are monolith brick type converters that flow very well. Drawbacks to hollowing out your cat include, emissions test failure, louder exhaust note, smelly exhaust fumes (yes, you will smell it in the car), and possible fine for tampering with a working cat converter. If you want to increase the flow of your cat, replace it with a universal cat made for a big V8/6L motor.
 

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mine was not working right, it was all burned up. i am going to put one back on after i get teh 02 sensors. and maybe up a glass pack to make it softer sound
 

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Be wary of so called "hi flow cats". These are just overpriced cats that can be had for half the cost. The determinents of flow are frontal surface area, length and density. Almost all after market cats have a density of 400 cells per square inch. Even the smallest aftermarket cats have flow ratings for engines up to 3L. The next universal size handles motors up to 7L and the largest handles motors up to 10L. Each one is physically larger than the next, which is what is determining their flow. Companies like Monza, Random Tech, etc... are just selling you 7L cats($100-$180) for your small displacement import engine. This same cat, from Catco, can be had for $60-$70 at jcwhitney.
 

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o2 went out. i needed to put new on but didnot have the $$$ for it rightnow. probly 200 for o2, cat. and work on it, VS $40 for pipe and gutted cat. and work. see what i mean.
 

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dj petey said:
Be wary of so called "hi flow cats". These are just overpriced cats that can be had for half the cost. The determinents of flow are frontal surface area, length and density. Almost all after market cats have a density of 400 cells per square inch. Even the smallest aftermarket cats have flow ratings for engines up to 3L. The next universal size handles motors up to 7L and the largest handles motors up to 10L. Each one is physically larger than the next, which is what is determining their flow. Companies like Monza, Random Tech, etc... are just selling you 7L cats($100-$180) for your small displacement import engine. This same cat, from Catco, can be had for $60-$70 at jcwhitney.
i have seen the Catco cats. but i have heard they are no better than the ones you can buy at a muffler like the one i got my work done at. and they are cheaper, i am going to get one put back on mine and 2 o2 sensor, it is to loud, what do you goes think about glasspacks???
 
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Discussion Starter · #9 ·
Number one I don't think that your car will produce enough horsepower to worry about the back pressure. Hollowing out your cat will probably not hurt. I mean if you have a free flowing exhaust how can that not help. The sound will not change that much unless you have a muffler or bigger pipes.
 
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Discussion Starter · #10 ·
There is such a thing as too little backpressure, but would not be caused by just gutting a cat. I'm talking about full open headers. By doing that you will likely, over time, burn up the exhaust valves. Also, too much drop in backpressure results in less torque for easy starts and allowing you to drive @ 2500 rpm instead of 3500. The benifit however is the ability to get exhaust gasses out faster which results in a better, more complete combustion so you do gain top end horsepower. Now just gutting a cat or replacing with a straight pipe may give a couple hp, but as mentioned new cats flow almost as good as a straight pipe so it would be minimal. If you don't have to worry about emmisions in your area then you'll be fine running a straight pipe if you don't mind the extra noise or smell.
 

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Woodnutz said:
Number one I don't think that your car will produce enough horsepower to worry about the back pressure. Hollowing out your cat will probably not hurt. I mean if you have a free flowing exhaust how can that not help. The sound will not change that much unless you have a muffler or bigger pipes.
the sound will not change? maybe it was all those racing stickers i added when i hollowed mine out...j/k...LMFAO!!!!

and BTW ive never smelled my exhaust gases inside my car... i wonder how the emissions is going to go, no cat, race engine and all.....
 

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the manifold is the primary, the downpipes are the secondary, the flex pipe is the third section to the whole manifold assembly. This section terminates at the cat converter. Removing the cat or hollowing it out, lengthens the effective third section and may harm the resonance and scavenging effects of a properly tuned exhaust.

Glass packs are no good. They will blow out and just get louder with age. For a good resonator it should use stainless steel wool sound absorption material like Genie or Exhaust Technologies.
 

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dj petey said:
Removing the cat or hollowing it out, lengthens the effective third section and may harm the resonance and scavenging effects of a properly tuned exhaust.

properly tuned??? for fuel efficiency, emmisions and attenuation maybe...
 
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