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Removing catalytic converter

91K views 32 replies 14 participants last post by  hoffmanestates 
#1 ·
Hi,
Assuming emission control is not a problem (which is my case, as there are no emission laws in my country), what problems or benefits will I get from removing catalytic converters?
Will O2 sensors go berserk?
Will I get fuel better consumption?
More power?

Thanks.
 
#2 ·
hey bud! yes more power will come from removing the cats! i just removed only my front small pre cats on my 01 v8 and i notice a way better pick up with them off. my mileage is a lil better to if i could stay off the gas long enough i would see a beter increase. my o2 sensors are ok no CEL as of 200 miles and if they do go beserk it will prolly be your downstream ones that do in that case there is a small cheap trick you can do to fix he CEL coming on issue. if this happens to me i will be doing the trick but the CEL coming on will not mess with any air/fuel ratios for your motor so your motor will run fine. You will just have a annoying light until you do the cheater trick for your downstream o2's. Thats if it even comes on.
Do you have the i6 or v8???

so more power because of the better less restrictive exhaust
better fuel if you can stay of the gas
and yes more power.

You may want to get a nice hi flow muffler to toss in there to complament your opened up front half!

I have a dynomax super turbo setup sounds great and not too loud.

hope this helps


Joe
 
#4 ·
In some vehicles, you will lose low end torque by removing the cats;found this out on my v6 SHO, and put high flow cats in after removing the stock ones for a while. if there is a notable improvement in pickup after removing them, it is likely the old cats were worn and getting plugged up, making the car run worse than it should.
 
#5 ·
yes on ford motors don't they tend to need and use the back prssure from the restricted air flow for a lil more torq. I had a Thunder bird and was reading alot about them needing the back pressure to run good. and like i stated i have the v8 i noticed the lil power gain and better fuel mileage.
Did you change any sensor or just get them mixed up when putting them back in? try to check all your connections to make sure they are all connected that was my problem its worth a shot :)


Joe
Joe
 
#8 ·
What is the cheater trick??? and will it cause any other problems by doing the cheater trick?

Jennifer
The purpose of the rear O2 sensors is simply to tell you when the cat needs replaced. They don't actually do anything for the motor.

On my Mustang there are 2 ways to turn them off, one is with a handheld tuner and the other is by making or buying MIL eliminators. The MIL eliminators are simply a resistor and capacitors wired to replicate a good O2 signal. It won't cause any problems with your engine (unless you keep your cat and it plugs up).
 
#7 ·
#9 ·
those dam cats..lol. so i have a 04 wj with the I-6, my friend had a header that came of his 95 jeep with six. so i figured i could cheat and get them dam cats out of thier,so i relocated the o2's big mistake my o2s went crazy and i lost low end power. well at that point i took of the header and bought one for my year, which used the cats. i gained more low end torqe than i ever had... take it or leave it, but i would leave in the cats...
 
#10 ·
You lost power because you relocated your FRONT O2 sensor. The front O2 sensor monitors the exhaust gases out of the engine. Based on it's measurements, it tells the ECU to add/remove fuel from the mixture. Messing with the front O2 sensor changes the air/fuel ratio. The rear O2 sensor is just to determine if the cat needs to be replaced. It does not change anything in the engine.

Are the cats on these vehicles on the headers? That's weird if they are.
 
#11 · (Edited)
thanks for the info but, i already knew how the o2's work. i didnt lose power because i relocated the the o2 in the wrong spot, it was a comination of things, like the header wasnt a 2 piece system like the manifold, and since i have two cats and 4 o2 sensors the computer is pretty picky,so i went and bought a two piece header that bolted up to my cats, than i relocated the o2's and bam i got my low end power back and the o2's are not wigging out... now jeep did make some wj's with just 2 o2's and with that system you can get by cutting out the cat's and it also lets you use the one piece header system like i tryed....
 
#12 ·
just wondering before I do this was it an easy job taking them apart and welding the new ones in? Not to much trouble or hassles other than the o2 sensors.
 
#13 ·
For future reference:

As long as the O2s located downstream of the cats are not reading too much oxygen, they will not "wig out" . Either they need to be spaced away from the piping with anti-foulers , or relocated downstream, etc etc. Sometimes they need no mods at all....it is a luck of the draw.

These systems are not rocket science, its just a matter of understanding what it takes to get what you want, all the while allowing the systems to work uninterrupted.
 
#14 ·
ya that i understand. I was just wondering if this is a project i can do before i go to work. I dont need it half apart because I cant seperate the cats from the headers
 
#16 ·
Just remove cats
 
#18 ·
okay so this is a weekend job. i dont have a downpipe ready to go. i was goin to cut out the two pre cats and put in pipes but it looks like a tight fit. with the flange and o2 sensors in the way
 
#20 ·
well i decided to cheat a little bit i bought a pair of cat free down pipes from and 01 just have to weld in the nut for the second o2 sensor
 
#24 ·
I hate to revive an old thread, but after searching, this is what I found.

I have an 04 4.7HO Overland.
I recently had the front two cats replaced.
Same old O2 sensors put back in.

The other day the exhaust down from the "Y"pipe came off. The techs did not securely fasten the rest of the exhaust which contains a straight run of pipe, the 3rd cat and the muffler.
When the "Y" pipe fell off, I lost most of my low end torque immediately.
I was planning on replacing my 3rd cat with a straight run of pipe to free up some flow. (No emissions testing in my state). But once I realized how much torque I lost, I have changed my mind.
My question is, why did I lose this much torque? I thought that freeing up flow would increase performance. Does the 4.7 HO really need that much back pressure to operate or do I have something wrong?
 
#25 ·
I hate to revive an old thread, but after searching, this is what I found.

I have an 04 4.7HO Overland.
I recently had the front two cats replaced.
Same old O2 sensors put back in.

The other day the exhaust down from the "Y"pipe came off. The techs did not securely fasten the rest of the exhaust which contains a straight run of pipe, the 3rd cat and the muffler.
When the "Y" pipe fell off, I lost most of my low end torque immediately.
I was planning on replacing my 3rd cat with a straight run of pipe to free up some flow. (No emissions testing in my state). But once I realized how much torque I lost, I have changed my mind.
My question is, why did I lose this much torque? I thought that freeing up flow would increase performance. Does the 4.7 HO really need that much back pressure to operate or do I have something wrong?
Without a datalog it is hard to say exactly.

I suspect one of two things: either the removal of piping, cat, muffler, etc increased flow and scavenging so much that it skewed the fuel trims/WOT AFRs.

Exhaust length is also an important factor in making power- typically, making the exhaust shorter more often than not will increase power (tq included). It's possible that the removal of the the downstream exhaust fell into that range where power can fall. It has alot to do with pulses.

Backpressure is mostly a myth used to sell smaller diameter pipes and more restrictive mufflers. Its better to think of it all in terms of flow, and velocity. Vellocity (and good scavenging) are the keys to producing tq. Torque x rpm = hp. ;)
 
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