Cat. Converter Removal or Gutting

[Ira]

Just wondering if anyone has any input on the removal or gutting of the catalytic converters on a 4.0L pushrod (91 model). Have done this before on non-computer engines but never on one of the more advanced ones. Someone told me you could do it on this model because the O2 sensor is before the converters but the muffler shop told me these engines would not run without them.

Anybody got any experience with this model?

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Ira

91 XLT 4x4

 

[Tony91Sport]

Ira,
some advice, unless you like being in trouble with the law, dont remove your cat. most muffler shops wont remove them, only replace, you also might consider the 4.0 DOES NOT like not having backpressure. it will run like crap. just a: leave it alone, or b: get a high flow cat installed

tony
91 Sport

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[The Godfather]

Kurts Kustoms has high flow cats for $70. http://www.kustomz.com/cat1.html

They're on the ranger page, but they should work for an explorer.

 

[Ira]

My model is a 91 and it only uses 2 converters. I had a 79 Trans Am years ago when unleaded fuel first came out and it had 1 converter. I had been told that gutting it would make a big difference, of course this was back in the days of very restrictive converters. I know that the newer ones are a lot less restrictive. Anyway, when I gutted it, it made a very big difference (30+HP estimated) and the engine ran cooler and got about 3 more MPG. That engine was carbureted and did not have a computer. I was just wondering if it would make a big difference on the newer engines.

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Ira

91 XLT 4x4

 

[Tom Wilk]

sprsvt,

Chances are, the multiple cats have different functions. Newer vehicles have this on at least some models. I'm not extremely familiar with cats, but I know that they will often put two in line to chemically convert two different exhaust gasses into two more benign ones. You probably have two on each bank of cylinders, rather than having them all after the pipes come together. I haven't counted mine, though I thought it only had two. I don't think that they make a multifunction cat that can do the job of two different ones, though I could definately be wrong. I hope this makes some sense.

Ira,

Your Trans-am of that era suffered in more ways than one. It probably had a 400 Cu-In engine with a 600 CFM quadrajet carb, with all that exhaust stuffed into one catalytic converter flowing at about half the rate of the carb. That certainly made for enormous backpressure. I don't doubt that the HP increased that much when you opened it up.

The newer engines, with one cat per bank of cylinders have greatly reduced restriction. think of it this way; your 4.0L inhales way less air than the 400 did, so it must exhale less also. And with two cats to share the burden, it can breath much more freely than the Trans Am did. My guess is that the difference between having the cats and not would be much smaller than what you had on the Trans-Am. Maybe a few HP from a low restriction pair, a bit more HP if the intake is opened up a bit as well.

I wouldn't remove them or bore them out altogether in any case, since they do serve a useful purpose and they don't tax the engine the way the old single cat systems (on a huge engine) did. I'm not sure how the electronics would react, but judging from what others have experienced with low restriction intake and exhaust, I think it could pretty much adapt.

Besides, I don't think that it is even legal for you to do it on your own car any more (it used to be legal if a commercial shop didn't do it).

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Tom

 

[S.Matsushige]

Ira-I have a friend with a '91XLT who gutted his cats about three years ago. It does run better but has a hollow echo sound. Other than that he has had no problems. I was tempted to gut mine when my cats went bad because of the performance gains my friend's XLT had but decided to replace it with a less restrictive one. My '91XLT doesn't have quite as much power gain as my friend's XLT, but at least I'm legal. As for the engine running, it'll still run. As for running like crap, my friend's XLT runs just as smooth as mine. As for being legal, his is not and mine is.

 

[Ira]

S.Matsushige,
Please give me an email. I have a couple of other questions I would like to ask you about.

Ira

 

[Extreme4x4]

I have heard from some people who have done it, that their vehicles ran very badly. Most small block engines require some restriction to run at their best. If you already have a cat-back system, then put on headers..... then gut the cats, you will have next to no restriction, and could lose a great deal of low end torque. Plus, I would rather keep them and know that my vehicles exhaust is less toxic than the air in LA. JMHO

 

[sprsvt]

I was looking at the cats on my 98 sohc, and it looked liked there were either 4 or 6 cats, i can't remember. If I were to get high flow cats, would i need 6, or could i cut out the existing ones and replace them with 2?

Also, what would the performance gains be, 1-2 hp, or possibly more?

 

[ganderso]

Ira (et al)

The bottom line is:

Removing or gutting your catalytic converter is both illegal and irresponsible. Don't do it.

Thanks!



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Guy A.
Ripley, TN

 

[S.Matsushige]

Ira-My email is scottm@belknap.com.

 

[91expl-sport]

By gutting the catalytic converter will it pass the emission test...

 

[kvo]

If you gut the converter and take it for an emmission test, a few things will happen:

1) you will never pass the emmission test.
2) they'll throw the book at you so fast you won't know what happened.
3) very expensive to pay the fines, get the repair fixed, court dates, etc...
4) definite possibility of getting your vehicle impounded, if the station is a hard nosed station or if it has been burned before.

Is it worth it?

 

[Ray Lobato]

Ira,
I copied this from a previous post about the same subject. It is from Skip Pendle, and I couldn't word it any better then he has. The following is Skips' answer and I think is very appropriate to your question. I happen to agree with him.

"At the risk of sounding like a goody-two-shoes, I am compelled to express a different viewpoint on this subject.

It is precisely the development of the catalytic converter that allows us all to have a choice of some pretty nice vehicles instead of some 25 horsepower, three-wheeled, electro-chemical wonder-wagon that the likes of Al Gore and his greeny buddies would have us all be happy with.

Pre-cat emission controls were terrible. I remember 350 cu.in. V8s with all of 140 horsepower, when they ran at all. I also remember the time when it was more common to see a solar eclipse than the San Gabriel mountains from San Fernando valley! If you haven't had this experience, treat yourself to a couple of days in, say, Mexico City. Just don't forget to pack an oxigen bottle or two. Heck, Tokyo used to have oxigen vending machines on the downtown streets...insert a yen, take a breath.

My point is that we all breath and we all pay the same "penalty", small as it is, of running our engine exhaust through catalytic converters. There are ways to open an exhaust system for power and E.T. gains that do not compromise the air we breath. Removing the cat is not philosophically any different than removing the mufflers and going off-roading through a bone dry forest. Sure, you've got a little more diggin' power and all the fires that you set are behind you, but you leave a hell of mess for the next guy.

And don't for a moment be thinking that a few vehicles with disabled catalytic converters is only a drop in the polution bucket. For most of our techno-nitwit politicians, a few drops are all they need to pass a law having us all being required to install new cats every year or some dumb similar thing.

My 2¢ plus for your consideration."

Anything worth doing, is worth doing right. Gutting your Cat is not doing it right.

And that's my 2¢
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Happy Wheelin'
Ray L. Dead Link Removed
97 XLT 4X4 4.0L SOHC



[This message has been edited by Ray Lobato (edited 11-17-1999).]

 

[The Godfather]

I saw this thing in the Parts America catalog the other day. It was a y pipe with a thing inside that would direct exhaust out one side or another. It was connected through a pull switch that mounted inside the truck. If you mounted this before your cats, you could run with a normal exhaust or you could pull the switch to send it out at the y pipe. It was only like $20 or something.

 

[danny]

The 91 Explorer doesn't have one converter per bank of cylinders, it has 2 inline after the Y-pipe connects. I gutted mine a while back and on the stock engine lost some power, so I re-installed a non-gutted one. After adding headers and a cat-back I got curious again and reinstalled the gutted cat. And this was after having the headers/cat on for about 6 months, BTW. The gutted cat gave it a very noticable increase all across the band. No loss anywhere. There is the annoying "echo" sound though...
Also, I got about 1mpg better mileage. But, at this point, I had done all my other mods as well. So, I wouldn't do it on a stock engine, but one with some bolt-ons makes a good improvement!
My SHO has one convertor per bank, on the other hand, and I wouldn't gut those expensive bast@rds!

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Danny
93SHO
91EB
www.hit.net/~danny/explorer.html