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Scott, the precats are just a part of the 3-catalytic converter system. They are little catalytic converters that just clean a little of the exhaust before it gets to the main cat. I gutted my front one already, and am about to gut the rear one today. It's pretty damn annoying trying to gut them though. I have an old main cat from my last stealth, and I gutted that, and it was relatively easy compared to the precats. The main cat is made of a ceramic type material, and can be broken easy. The precats are made of some kind of metallic stuff, and is a bitch to get out. I had to use a drill, and keep drilling holes into it until I could pry the edges out. After only gutting one precat, I could feel a little difference, and a little bit louder exhaust. If I had to guess, gutting one pre-cat added 3-4 hp.


Jason
92 Stealth R/T TT
 
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I keep reading references to pre cats and the gutting of them. I understand they are located after the exhaust turbos, but what are they and what do they do?

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Scott
92 tt
 
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Won't gutting the precats increase the pollutants to the main catalytic converter, causing it to fail sooner?

Also, will the emissions measured at the tailpipe increase? Emissions testing is required here in Phoenix and can be expensive to fix if you fail. Sounds like something you may not want to do if you are tested.
 

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Gutting the precats does increase pollutants, but won't cause the main cat to fail. I don't think catalytic converters can fail. They are a really simple device that can only go wrong if clogged by foreign material, which would probably not happen since only gasses from the engine are going through, or by the material inside breaking. The cat is just a ceramic looking material that allows the exhaust gases to pass through. After about 20 minutes of running the engine, the ceramic in the cat gets hot enough to burn out most of the pollutants. The ceramic has square holes running through it, almost exactly the same pattern as a screen door. I actually just got my main cat out today and put one back in that I hollowed out. Really stinky, but more power. I only have one pre cat left, and that'll go probably on sunday. You should be ok to pass emissions with just the main cat, but with no cat, you definitley won't. I have to get emissions here too, but not for two years. the thing is that I have my original cat for the car and can bolt that right back on before I get tested again, then take it off after I pass. It's not the best idea to do if you are not really into alot of power, but well worth it to me.

Jason
92 Stealth R/T TT
 
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