De-Cat a non turbo? - Alfa Romeo Forum
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(Post Link) post #1 of 17 Old 07-04-16 Thread Starter
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De-Cat a non turbo?

Hey guys.

Been reading about de-catting a 156 2.0 TS.

I may be wrong but this is what it seems it takes.

A set of 2.5 manifolds. Because they didn't have the cat. I'm not sure how the V6 manifolds would fit.
Slightly moving the Lambda back as it works better away from the heat. And can get a better reading.
And just having an exhaust place cut out the last one.

I am not to sure on this as people seem to have different ways of going about it.

Some people just say cut the cat out and replace with a straight piece of pipe.

The car i have is a '99 model. I don't know much about CF1, 2, 3. How would I check that. And what is the best way to de-cat without causing ECU issues. I have access to a machine shop, so just cutting my pipes and re-welding in straight pieces wont be an issue. As long as this wont harm the car.


More importantly. Does de-catting a non turbo car make any difference. This is the first non turbo car I have had and have always been told de-catting is just a turbo car thing. But if it will give me at least a 5bhp gain I may look at it.

Lastly is there any other ways to get a bit more out of the car without opening the engine or bolting on a turbo.

My main goal is to get a bit more grunt on the pull off.

Thanks guys. Sorry for asking a question i have seen asked a lot. I just have no idea what the CF thing is or miss understand the 2.5 what what.
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Decatting will always give more power. Mainly because you want all exhaust gases to escape as quick as possible. Works on all engines.

Cat's slow the gas down to be processed and cleaned. A through pipe doesn't.
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Originally Posted by Special156 View Post
Hey guys.

Been reading about de-catting a 156 2.0 TS.

I may be wrong but this is what it seems it takes.

A set of 2.5 manifolds. Because they didn't have the cat. I'm not sure how the V6 manifolds would fit.
Slightly moving the Lambda back as it works better away from the heat. And can get a better reading.
And just having an exhaust place cut out the last one.

I am not to sure on this as people seem to have different ways of going about it.

Some people just say cut the cat out and replace with a straight piece of pipe.

The car i have is a '99 model. I don't know much about CF1, 2, 3. How would I check that. And what is the best way to de-cat without causing ECU issues. I have access to a machine shop, so just cutting my pipes and re-welding in straight pieces wont be an issue. As long as this wont harm the car.


More importantly. Does de-catting a non turbo car make any difference. This is the first non turbo car I have had and have always been told de-catting is just a turbo car thing. But if it will give me at least a 5bhp gain I may look at it.

Lastly is there any other ways to get a bit more out of the car without opening the engine or bolting on a turbo.

My main goal is to get a bit more grunt on the pull off.

Thanks guys. Sorry for asking a question i have seen asked a lot. I just have no idea what the CF thing is or miss understand the 2.5 what what.
Yes you have MASSIVELY misunderstood that!!

You can't fit V6 manifolds to a TS engine and you wouldn't want to anyway.

Your 1999 2.0TS has a single Cat, which is under the car.
There are NO Cats in your exhaust manifold.
You simply unbolt the Cat (M8 nuts/bolts) and bolt in a decat.
Because your engine only has a single Lambda sensor, which is located before the Cat, it neither knows nor cares that the Cat is missing.
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how much hp gain from decatting? roughly??
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how much hp gain from decatting? roughly??
For a v6 removing the 2 manifold cats only and leaving in the 2 main cats - Gain of approx 20bhp.

For a 2.0ts, removing the 2 manifold cats only and leaving in the single main cat, gain of approx 5bhp.

I can't comment on single CAT systems but I wouldn't recomend it.
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Oh wow. That easy. Would be interesting to now how much gain I could get out of this. But if its as simple as unbolt this and bolt on that then there really is no reason not to.

Out of curiosity. Is the 2000 model a single cat as well.
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Out of curiosity. Is the 2000 model a single cat as well.
Depends what part of the world you are in.
In Europe they changed from single Cat with single Lambda (CF2) to multiple Cat and multiple Lambda (CF3) in September 2000. Some markets outside Europe kept the single Cat setup for longer.
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Originally Posted by ransoman View Post
For a v6 removing the 2 manifold cats only and leaving in the 2 main cats - Gain of approx 20bhp.
That is a bit over optimistic.. FULL cat delete with free flow exhaust comes more close to that number
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For a 2.0ts, removing the 2 manifold cats only and leaving in the single main cat, gain of approx 5bhp.
That is realistic
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I can't comment on single CAT systems but I wouldn't recomend it.
Even easier that manifold CAT's - just not legal in UK / EU

If you are thinking about de-CATTING, do it - albeit be aware of your local rules. In no TS / Busso have we picked up ECU errors - no CAT foolers needed
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That is a bit over optimistic.. FULL cat delete with free flow exhaust comes more close to that number
I am confusing myself as the 260bhp figure quoted after precat removal is for a GTA with 250bhp stock (10bhp). On paper the 3.2 is 240bhp but we all know it is the same as the GTA so really has 250bhp. Therefore cat removal increase is nearer 10bhp.
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I live in South Africa. No problems with removing the CAT here. Think I will just unbolt the CAT, cut it off and weld a straight pipe on. Can then just bolt that in. Easier then getting under there to weld it up.

Is there anything I can do to get the lower end up. The car really needs more pull from low speeds.
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Is there anything I can do to get the lower end up. The car really needs more pull from low speeds.
Not really, just make sure everything is working properly, air filters replaced, etc..

You can try removing the silencer box that fits on the side of the air filter housing and fitting the pipe that the V6 uses in its place. Autodelta used to sell that as a 100 "upgrade", but was actually a 20 std Alfa part...!!
You can also try taking out the cone that passes through the centre of the air filter.

Don't throw the bits away as you may want to put them back in.

Some ECUs work better with, some without.


Also, put your location in your profile. It will help people give the best advice.

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Hmm, post just disappeared.

Location added.

I will do the V6 pipe swap as well then. That with the de-cat and balance belt off should make a difference. I see people saying after each of these mods they feel a difference. So with it all done it should be nice. Not looking to spend crazy money and do anything that requires the engine gets opened, so these are perfect.

Thanks for the help guys.
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I live in South Africa. No problems with removing the CAT here. Think I will just unbolt the CAT, cut it off and weld a straight pipe on. Can then just bolt that in.
Jip - try keep it matching the OEM bolts as much as possible - sure it'll work well.

You in SA - come introduce yourself to the SA crowd and see what we are up to.

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Lambda sensors work better in heat.
That is why most of them further down the exhaust are heated.
If they are to far away they will soot up.
Lots of good info on the Tech Edge website, if you can find it.
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In no TS / Busso have we picked up ECU errors - no CAT foolers needed
Had my silencer deleted last week and wanted to do the twin cats as well (147 GTA) but the guys balked when they saw the sensor in the pipe after the cats and said to look into that before they would touch it. Are you saying that it isn't a problem and the sensor won't cause any problems when the cats aren't there any more? Not the manifold cats, the ones underneath
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Had my silencer deleted last week and wanted to do the twin cats as well (147 GTA) but the guys balked when they saw the sensor in the pipe after the cats and said to look into that before they would touch it. Are you saying that it isn't a problem and the sensor won't cause any problems when the cats aren't there any more? Not the manifold cats, the ones underneath
Yes all sensors back to +/- where they were - all good
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I live in South Africa. No problems with removing the CAT here. Think I will just unbolt the CAT, cut it off and weld a straight pipe on. Can then just bolt that in. Easier then getting under there to weld it up.
You can cut it up but then you can't put it back if the rules change!

Quote:
Originally Posted by Special156 View Post
Is there anything I can do to get the lower end up. The car really needs more pull from low speeds.
Unlikely to help much. You need torque for lower speed pull not HP and the TS engine comes on song at around 3000rpm.
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