catalytic converter question

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keVIIIn

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With more and more exhaust threads started lately it has got me thinking about what I want to do with mine soon. I was planning on buying a mandrel bent dual 2.5" system off ebay similar to the one nolimit wanted. I however was thinking of using magnaflow mufflers out back with just an x pipe instead of the magnaflow "x muffler" in the center which would obviously require getting rid of the 3rd y pipe cat. Occationally I have noticed the rotten egg smell upon hard acceleration or at highway speeds which leads me to believe one or more cats are clogged. I know i've heard many people say usually the 3rd cat is the one that gets clogged over the years but whenever I get my exhaust done I was contemplating hollowing out the 2 front cats also to further eliminate the clogged cat issue.

So my question is has anyone done this with a mark viii before, and run into any problems? Also how would you go about hollowing those cats while on the car, is that even possible to do without removing them? Is it true that there shouldn't be any check engine light problems with the 93-95 cars (EEC IV) which only run 2 oxygen sensors opposed to 4 on the 96-98 mark viiis? Any tuning required if you eliminate or gut the two front cats?

As a disclaimer..yes I know it is illegal to remove or gut catalytic converters but it doesn't matter for me considering they don't emission test anything 1995 and older anyway (at least in my area).
 
Kevin, I have heard that hollowing out the high flow cats really make the car sound like sh!t. They're really not that restrictive and that's why most just leave them there and then finish out the rest of the exhaust. I too get the smell sometimes but that's all about to come to an end.

I'm sure there are some youtube videos of exhaust clips with hollowed out high flow cats. I'm leaving mine as is.
 
NoLimit95 said:
Kevin, I have heard that hollowing out the high flow cats really make the car sound like sh!t. They're really not that restrictive and that's why most just leave them there and then finish out the rest of the exhaust. I too get the smell sometimes but that's all about to come to an end.

I'm sure there are some youtube videos of exhaust clips with hollowed out high flow cats. I'm leaving mine as is.
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I'm not too concerned about the sound difference, I just want to gut those 2 front cats so I don't run into anymore problems down the line with them getting clogged. I'd hate to spend the money on a whole exhaust system and get rid of the 3rd cat and then find out it's actually the front cats that are the culprit.

Not only does it give me the rotten egg smell but when it does that usually it throws a CEL also and starts to misfire slightly around 1000-1200 rpm. Not sure if there is another issue but it seems like it is related to the clogged cats maybe messing with the O2 sensors. If I shut the car off and let it sit for a few minutes and restart it the CEL is gone and it runs normally..or sometimes it even corrects itself after driving for a few miles.
 
Exhaust

I put the same system on my 98 and love it, no drone no smell and sounds great. Just delete the 3rd cat and don't play with the front two, not worth the hassle. I am doing this same system for a customer next month. The only part I don't agree with is why people use the 2 1/2 system. I only use the 2 1/4 system and it fits better with less clearance problems. If you look inside the front pipe of the factory system coming out of the cats, it is only 2" inside a 2 1/4 pipe that does nothing over it. Unless you are putting headers and a different intake on, it is like blowing into the wrong end of a funnel. JMHO Thanx Bruce
 
true, 2 1/4" pipe would probably suffice, but the cost is the same for the 2 1/2" on their website, and larger diameter exhaust always sounds better (in my opinion) it has a more throaty sound..performance wise makes no difference but if theres no price difference..why not go with the bigger pipe.
 
My brothers old 93 had lms exhaust, X pipe, and no cats one hollowed and one pipe and it sounded very raspy at Wot and had a very rich smell.
 
Dont go 2.25, put 2.5 let that 4.6 breathe easier. As for hollowing out the cats it will make the car sound terrible, just get some hi flo cats and throw those in if you want, they have very little restriction and will be noticeably louder than stock cats.
 
Being the cats are at the front of the exhaust I really don't think if they were hollowed out they would change the exhaust note much if at all, I could see it maybe being a little louder but that's not an issue for me. If it were easier I would just rip the damn cats off but since one is integrated into the exhaust manifold that isn't very easy to do. Basically I don't want to drop the whole k member to replace the stock manifolds with something different whether its cobra manifolds or headers, since its a fairly large project on my only vehicle available to drive.
 
dont waste your time and energy hollowing out 3rd cat. get rid of it i put the lms system on mine, with headers its LOUD but leaving the reg exhaust manifolds it will sound great, +1 on running 2.5". there are no emissions here but where you r idk the emissions laws. some states just do visual others the sniffer. with the 2 on the manifold even with visual you might get away with it./
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and video for good measure
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NoLimit95 said:
He doesn't want to hollow out the 3rd cat. He's talking about the two high flow cats.
Click to expand...

Yes that's correct, all I want to do is chop off the exhaust just behind the first 2 factory cats, add an x pipe with the mandrel 2.5" dual system and magnaflow mufflers. I know at least one of the 3 cats are clogged since I get the rotten egg smell sometimes and I don't want to spend a bunch of money on the exhaust system and still have the 2 front cats clogged..this would defeat the main reason for me getting a custom exhaust done. I know there are other ways around the front cats but this requires me to remove the stock manifolds and either modify them or replace them, but I am not going to drop the front k member to accomplish this since my car is currently my DD, not to mention that can get pretty involved.
 
One thing about it Kevin is that if the exhaust is installed properly and removable just after the high flow cats, you can always come back after the install and drop the front of the exhaust and then hollow out the cats, if you think they're contributing to some sort of problem but I think you'll be ok with leaving them as is. The smell you're smelling is coming from that 3rd cat most likely. Without hollowing them first, I'd give them a try with the 3rd cat and res removed and X-pipe installed and new mufflers. If you feel like the high flows are giving you a problem, they can always be gutted but if you gut them, make sure you really gut them. I have heard of some people mention gutting the high flows and then finding out that they left pieces inside them, not knowing of course.

Then those pieces then make their way to your new mufflers and start stopping them up. Not a complete stop up but just knowing you now have pieces of the inside of the high flows inside your mufflers and something may even get caught in the X and cause the equalization of the flow to not be right. Just something to think about before you do it. I'm very very close to just ordering some new high flow cats but I'll never gut mine. I would just buy 2 new ones and have the old ones cut off and the others welded in place. If the exhaust guy recommends not having any at all, then that can be done too. No inspections here in AL. either. As long as you're not running straight headers around here, they don't care.
 
That's true nolimit I forgot about putting flanges just before the x pipe to make it removable if necessary, I may just do that then. Down the line when I get another car Ill probably have the k member dropped and replace the stock manifolds with something better..probably cobra manifolds as I don't really want to spend 800-900 bucks on headers.
 
You do not have to drop the kmember to remove either manifold... for the driver side, remove alternator and brace engine, remove rag joint and calapse the steering rod inside itself (just push it upwards) it telescopes. Then remove the motor mount, then remove manifold.
 
keVIIIn said:
That's true nolimit I forgot about putting flanges just before the x pipe to make it removable if necessary, I may just do that then. Down the line when I get another car Ill probably have the k member dropped and replace the stock manifolds with something better..probably cobra manifolds as I don't really want to spend 800-900 bucks on headers.
Click to expand...

I'm having mine put where they are now so that the exhaust comes down just as it does stock. Hopefully it works out that way. I'm also not spending money on headers. I just want a breathing exhaust. I'm not going to be racing or anything. Done put enough into this thing as it is.
 
also considering cobra manifolds..
thinking my catalytic converters have seen better days.
i'll do that and dual exhaust this summer i suppose.
 
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