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Decatting


nrgizerbunny
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Well today I spent the day decatting.

I bought a second hand midpipe from a scrapped Corolla and then chopped the cat out, once that was done I knocked the insides out and rewelded it back together.

I started by figuring out how the OEM lambda sensor works so I tapped the signal and put my oscilloscope in to get the waveform

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Here's the cat ready for chopping

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Here it is chopped

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A bit of screwdrivering later and all that junk is removed from the middle

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And a bit later the cat is welded back together!

388055_10150897325385634_549210633_21624601_865652817_n.jpg

I also welded in an extra boss for my wideband.

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That's an interesting job there, did you notice any difference in performance ?

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interesting............ looking forward to knowing if this works. one word legend

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it's going back on the car tomorrow. I'm having a few issues getting my O2 sensor replicator to function correctly at the moment. I was pulling a value from the car that was below ground voltage so I must have a ground loop in there somewhere which I need to sort.

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got the O2 problem sorted. Just need to frig up some electronics to get it work correctly.

Critical Values in case anyone needs them for future reference

Vhigh is 660mV,

VLow is 20mV

Frequency varies between 1 every 2-4 seconds.

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so how exactly have you done this ,baring in mind i will need to tell this to the exhaust place , im guessin a wideband o2 sensor .

and it being pulled away from the main exhaust stream via spacers

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so how exactly have you done this ,baring in mind i will need to tell this to the exhaust place , im guessin a wideband o2 sensor .

and it being pulled away from the main exhaust stream via spacers

I really don't understand your question!? I've read it through a few times but still don't get it. And before anyone suggests it - No I am not drunk!

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I think he means a longer boss so the sensor sits further out say a inch to the side.. so the sensor picks up more o2 as the cat is not doing its ting.... are you planning on packing the cat with wadding? or just empty?

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well that's how I guess it will work....

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I've left all of the CAT internals out, as this is a decat. I've kept the spare exhaust for MOT time. I didn't bother with any of the spacers and all that stuff. There are too many variables, hence I went for the electronic solution.

I first located the O2 sensor connector and then proceed to chop it and figure out what each of the wires did.

There are four

Black top left = Heater Ground

Black top Right = +12V when ignition is on, this supplies the heater

Blue Bottom Left = Signal

White Bottom Right = Ground

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Then I tapped the ground and +12V with scotchlocks and a butt connector.

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Finally I tuned the O2 sensor in with my Oscilloscope, you could do this with a multimeter but it will just take a bit longer.

312589_10150899057950634_549210633_21641687_954693084_n.jpg

It might take a little more fine tuning but you get the idea

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I'll report back tomorrow to see how much difference in power it makes, if any.

The Exhaust does not sound any louder which is what I wanted, perhaps a little bit more throaty but thats it.

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so how exactly have you done this ,baring in mind i will need to tell this to the exhaust place , im guessin a wideband o2 sensor .

and it being pulled away from the main exhaust stream via spacers

I really don't understand your question!? I've read it through a few times but still don't get it. And before anyone suggests it - No I am not drunk!

no but i think i still was drunk from last nite .

anyway il stop the jibberish and just see how you get on .

i really want a decat myself though, even if its a extra 3bhp its still more

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Would you not get a better sound by removing the silencer between the cat and back box?

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why didnt you just chop the cat out and weld in a straight pipe if you have another one for mot time?

If I reused the empty cat, the ever so slight imperfections in my cuts would line up and mean the exhaust was still in alignment, If I used a spare bit of pipe that would no longer be the case.

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Nice one, i noticed a big difference in power after decating my car, i used a boss to extend my sensor.

Would you not get a better sound by removing the silencer between the cat and back box?

Not really i chopped mine out and didnt make much of a difference.

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you could sleeve it? the sound will resonate because of the big chamber and wont give the best flow, i did the same on my old zetec s and it was better with a pipe welded in than the cat smashed out. just my thoughts though :thumbsup:

Would you not get a better sound by removing the silencer between the cat and back box?

Not really i chopped mine out and didnt make much of a difference.

because the centre box is an absorption type box which will cancel out high frequency sound, basically the same as many of the "jap style" cans, its the rear box that does all the work

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FLIPPING HECK!!!

DECAT = 15-20PS!!! (I Think)

It feels like the car is in a lower gear, it just pulls.

No Engine lights as yet but I think if it was going to come on it would take 3 trips to trigger so I'll have to wait a while.

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FLIPPING HECK!!!

DECAT = 15-20PS!!! (I Think)

What's all the rage about PS these days? What's wrong with BHP?

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FLIPPING HECK!!!

DECAT = 15-20PS!!! (I Think)

What's all the rage about PS these days? What's wrong with BHP?

You are in pounds shillings and pence, move up to metric :lol:

Kingo :thumbsup:

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15-20ps is that just your bum dyno lol

surely 5bhp at the maximum , it just didnt look like there was that much you took out the cat ,its only a small one compared to alot of cars .

i mite give it a go in the new year along with a full mandrel bent system.

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FLIPPING HECK!!!

DECAT = 15-20PS!!! (I Think)

What's all the rage about PS these days? What's wrong with BHP?

You are in pounds shillings and pence, move up to metric :lol:

Kingo :thumbsup:

Lol, I'm happy in imperial :)

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15-20ps is that just your bum dyno lol

surely 5bhp at the maximum , it just didnt look like there was that much you took out the cat ,its only a small one compared to alot of cars .

i mite give it a go in the new year along with a full mandrel bent system.

Well people put cat back steel bent things on the exhausts and get 10hp.

The biggest restriction is the cat, it has the same surface area as a football pitch. Take that out and see what happens. And yes it is my highly calibrated bum dyno.

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