Gutting a cat, What are the disadvantages?
 

I know that gutting pre cats opens up the exhaust to flow better, but the O2 sensor is downstream from my pre cats on the M103. Will "opening" them up have any adverse effect on the signal to the O2 and ultimately the ECU?

The O2 sensor tells it like it is. If there is unburned fuel in the exhaust flow that the pre-cats would have caught, the O2 sensor will communicate such to the ECU. I don't think it will be a problem since those pre-cats can't be very effective even when new.

You'll likely get a check engine light if you remove a cat that is between two O2 sensors.

Sixto
91 300SE
87 300SDL

You'd be amazed at just how effective those precats are. I'd leave them be, if you going to pull a cat, pull the rear one.

Dont gut 'em anyway, drive a pipe all the way through, the openess of the chamber causes a backflow effect that robbs more power than the cat does.




Joe

My only experience with "punching" a cat resulted in a noticeable improvement in power. But, that was a simple system with the sensor in front of the main cat. As ticky as the KEIII injection system is, I just want to know if it's going to create more problems than it cures. By the way, this is on an "off road" vehicle, since it already has clear blinkers!;) ;)

The O2 sensor is actually a lambda sensor. This means that it is measuring temperature. The effect of the catalytic converter being opened up should have no effect one way or the other.

Now to my first thought when reading your post subject. Gutting the cat will use up all nine lives at once.:D

Good luck,

Thanks Larry! After I made this post I went out to the garage and got to thinking, You know, if somebody else had asked this, I would have said "yeah the disadvantage is that it's gonna be hell on the cat"!!:p :p

Wait...So on my car, I really have 2 cats? Is that that smaller looking cat that you can see from the engine bay at the end of the exhaust manifold? Iv been wandering what that was forever. I ended up asking my dad if that was a CAT or not and he didn't know either.

Disadvantages? You are screwing with the enviroment and it is illegal:rolleyes: :rolleyes:

Everyone,

Yes, the little one near the exhaust manifold is called a light off converter. It heats up very quickly after the engine is started to decrease emissions during the warm up period.

Yosshimura,

Yes, this does have emissions ramifications, however, WITHOUT the converter, you emit hydrocarbons, WITH the converter you emit sulpher(sp?) This is six of one and a half dozen of the other. The biggest environmental advantage to the converter was that when it came out in 1975, it forced everyone to move away from leaded fuel. Otherwise the catalytic converter was just another hoax put over on us by the infinitely wise US Congress. You know, anyone who is elected to congress is automatically an expert on any subject in the world.

Have a great day,

Hold on here partners!! Before this turns into a battle of Good and Evil let me clarify something!! I'm not talking about removing or altering the main converter. Even though we don't have emissions inspections where I live I would'nt do that. I just think it's overkill to have three cats on a car!! I am not aware of other manufacturers putting that many on their cars. But in Larry's defense, why is the United States the only country that has emissions laws and a freon control? It's OK for the rest of the world to pollute but not US.

I did it on my BMW and felt a small diffrence in the pickup sounds better too. If you do punch out out let it hang and drive around for a little while so you blow out the small parts of metal.
;)

Correction to a previous post:
Not only the USA have emission laws and restriction on FreonR12-
Several European countries have endorsed similar laws and regulation. North of the border (called Canada) also have very strick emission laws, very similar to the California laws.
I can't see why there are some many people bashing about cat. This is not where the restriction is in an exhaust system. The biggest restriction is generally at the exhaust manifold and muffler end, not at the cat.
You can open/remove/enlarge the cat as wide as you wish, there will not be any significant performance increase, except the one ''perceived''
JackD

A lot of people don't do it for preformance they do it because of the cost of replacing it.

I am not the brightest light in the hall but I do know this.... all internal combustion engines are basically air pumps. If you restrict the intake or the exhaust, then you deminish efficiency of the machine. Race engines can race because they can BREATHE . Any improvement in this capability results in a power gain. All I'm trying to do is free up a horsepower or two. And, if the fuel mileage increases, I won't complain!! ;)

Other countries emissions
 

Hey Captain Carageous,

I was following the discussion about the pre-cat and if you should gut it. I wanted to respond specifically to the statement of the US being the only country to have emissions testing...and freon laws

Germany, all the Scandinavian countries as well as other east European countries have vehicle emissions testing, freon laws I am not sure.

Canada, in BC and Ontario, Australia also do emissions.

as a post script, my thinking has always been, if a part is on a vehicle, the engineers designed it that way for a reason. All the parts make up the whole and they are interelated acting together, often removing or destroying one effects the others functionability/performance. It is best not to gut the cat.

I stand corrected on the controls comments. BUT on the issue of leaving something original, well, I think it's our duty and responsibility to modify and improve our vehicles. What fun is it to buy a car and just drive it ??:( In the spirit of Tim "The Tool Man" Taylor: "I can modify that to get more POWER":D :D

ALong time ago I had to replace the cat on my 420SEL. I suspected a clogged cat because the car had no power. If you were to floor it, it would not go over about 50 mph unless u let off the gas and let it upshift. This was because the engine could not get over 5000 rpm. The car was also silent as could be. After many years with the new exhaust system (aftermarket), the new convertor started to deteriorate and rattle. Discusted at the idea of spending another $1000 on a cat, I guttet it instead.

As far as power is concerned, there maybe a little more. But I think it is just perceived as more power because it is a little louder and more bellowee(sp?). One thing I noticed for sure. The exhaust STINKS! Went on a road trip with some buddies, after a few miles they said they had to lead because my exhaust was so bad!! I also noticed that since i gutted the cat, I have alot more white smoke puff out of it when I start it up in the morning, and when i floor the car, it emits dark smoke. I think the cats filtered this out before. maybe there is something wrong with my motor where it keeps going thru cats, but instead of spending time and money to know, I took the easy way out. Hope this helps.

More on..gutting a cat
 

Hey Guys,

I felt obligated in the interest of science to put my 2 cents worth in...again.
Larry Bible stated that a cat emits sulpher compounds, technically not true, a cat converts HC to water ( H2O ) CO to CO2 and excess O2 to H2O, gasoline in St. Louis has the highest supher content of all gasoline in the country, this reacts only with the air (O2) in the combustion chamber to create sulpher dioxide-SO2, this will contribute to the destruction of the cat, SO2 once emitted in the exhaust, will react with rain to form sulphuric acid, ie. battery acid, also called "acid rain".
A further note, here in St. Louis, we have 1.5 million vehicles driving 50 million miles PER YEAR! emitting around 44 tons of HC, 660 tons of CO and 110 tons of Nitrous oxide compounds every year, and thats the CLEAN CARS, one city, one state, all that crap floats around the world.

Yes, cats are important

I have decided to leave mine alone. I can't see any advantage to modifying thse pre cats.

Cats restrict power: Proven difference.
 

Back in my hot rod days, On my 94 Z28, I removed the cat and the car FELT noticeable faster.

However, I never took seat of pants or sound as seriously as most. I would always take the car to the track after a change not to race people but to test/see if it REALLY made a difference. In this scenario it turns out the seat of pants indicator was correct. After numerous runs all thing being equal, I consistantly ran 2 tenths better during the quarter mile run with the cat REMOVED(13.8's to 13.6's). About 2wice as loud though. Great on a american v8, not so sure it would sound good on a 6cyl or diesel although a turbo diesel may not be as loud as normally aspirated diesel..

Basically, in the 94' Z28 5.7liter eng. with 275 factory horsepower this equated to approx 20hp difference based on quarter mile times and other factors. I do not know if all cats are made equal and on smaller engines there may be quite minimal difference and too much loss of low end to even matter. I guess on that car I didn't feel much loss in low end considering it put out 325ft pds torque @ 2000 rpm in the automatic.

I can see that there would be a difference by modifying the main cat. I've done that (years ago, I think the statue of limitations has run out by now), I was referring to the two small pre cats near the engine. Someone has suggested that they serve the purpose of "cleaning" a cold (rich) motor. I don't see any benefit with tinkering with those.

I think you are correct Cap. For me, the only way to really know for sure was to try it out. The Mercedes is much better engineered than the chevy in my o, so I wouldn't fool with it to much although for the real speed enthusiast you could probably make it go faster but prob also sacrafice some other benefit..

The truth of the matter is, I'm approaching geezer age, so comfort and dependability in the daily driver is more important than performance. I still have my toy to play with when I want to get my heart rate up. " I love to hear 7000 rpm, but not on a regular basis anymore!!:)