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Old 06-16-2008, 05:14 AM   #1
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Impact of removing catalytic converter

I am considering removing the CC on my Mits 2004 Galant.

Good news is that I live in a state that has no emissions checks so I don't have to pass annual emission tests.

I am interested in what are the technical hurdles of doing this?

I want to just pipe it straight through and of course hold on to the CC in case I need to replace it in the future.

If I yank it out of there will the ECU start to complain?

Has anyone pulled theirs out? What is the increase in mileage?

Any thoughts feedback or suggestions are appreciated.

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Old 06-16-2008, 05:31 AM   #2
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I wouldn't for at least two reasons.

$2500 fine for violation. Doesn't require an smog check just a visual inspection.

Your emissions system may have a sensor after the cat and if you remove the cat you may get a check engine light.

It won't make any difference in mileage unless its plugged up. If so used ones are not very expensive especially considering your old one has significant scrap value.

Dont know your mileage but your emissions system is covered by a mandatory 5 year 50,000 miles federal emissions warrantee.


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Old 06-16-2008, 06:33 AM   #3
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I have heard of people gutting their cats for power. that is they just run a pipe through it with a sledge hammer. that way it is still physically there.

not sure if that will help with FE though. I guess it will be less restriction in the exhaust but I still think it will be minimal.
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Old 06-16-2008, 09:44 AM   #4
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i did this mod with my subaru wrx gutted the stock up and down pipe, I definitly felt more power and more mpg. I am able to hit 32mpg at 55mph and almost at 300 horsepower
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Old 06-16-2008, 10:03 AM   #5
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My brother removes his CAT after the emissions test every year, he can get 320 miles in the FWY from a tank of gas with the CAT and 380 with it removed, more power means more FE.
Water is fuel, I just don't know how to make it work yet.
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Old 06-16-2008, 10:34 AM   #6
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I can go 700 miles on a tank with my CAT in place.

And then there's this:
1 hp gain over stock (151 vs 150) with a high-flow cat
2 hp / 1 tq gain over stock (152 vs 150 / 108 vs 107) with a straight pipe

Hardly worth the effort. Try something like a grill block or higher tire pressure, and some "adjusting the nut behind the wheel" for real gains.
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Old 06-16-2008, 10:40 AM   #7
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PaleMelanesian - thanks for the comments,
I have already tried everything you suggested with a great deal of success.
Now looking to tweak further
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Old 06-16-2008, 04:45 PM   #8
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I tried this about 15-20 years ago with my '79 Chevette. My problem was that it only got 20mpg (maybe up to 22) no matter how I drove. Easy on the gas, romping on it, city, freeway, didn't matter. I poked at that car for almost 200k miles trying to figure out what the problem was. One of the things I did was remove the cat...actually ran straight piped that tank. Only result was a headache from the noise and a stern look from a deputy sheriff.

The cat's there for a a kid I grew up in Smoggy LA...sometimes in the summer, especially back in the '60s it got pretty much impossible to get a deep breath! I appreciate anything which helps get the crap out of the air!

If your cat's plugged, you'll KNOW it! The car will just have no power. Discovered this on the way to work one morning...climbing my steep hill (1.8 miles to gain 800 feet altitude) in my Lincoln...suddenly had no power at all, but the car sounded OK. Everyone passing me (my boss gave me a strange look!). Crested the hill and was able to go fast again. Just couldn't accelerate.
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Old 06-16-2008, 05:38 PM   #9
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on that new of a car, you'll gain little to nothing from removing the cats. power/FE gains are most noticeable in turbo engines and cars at WOT. hypermilers rarely if ever enter the range where losing the cat improves the situation (high revs high throttle). that being said, every engine/car responds differently.
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Old 06-16-2008, 06:02 PM   #10
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You Will F- Up That Car Very Bad If You Remove The Cats!!!

less lurking and more working
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