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Thread: De-cat lower or increase the performance on a standard remapped car?

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    Regular Member Torque's Avatar
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    Default De-cat lower or increase the performance on a standard remapped car?

    This has always baffled me and I've asked the question before on the mkiv forums when I had a Golf GTTDi and rang numerous tuning specialists and had different answers from all of them.

    Obviously a standard remap is set to run with standard existing parts, I know the only thing that doesn't make a difference is changing the induction which will increase the performance by a small amount regardless.
    So the 1st argument is that you would lose performance as the maps set to run with the cat on the car. You would then need a custom remap to get the extra performance from the decat.

    The 2nd argument is that how are you able to lose performance when your letting the gases escape quicker and letting the exhaust breath more freely.

    To this day I still don't know the answer and would love to know the official answer. Anyone have a standard remap and a de-cat and did you gain or lose perfomance?

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    Regular Member zafira's Avatar
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    I did de-cat/dpf my vectra before I remap. And definitely gain performance. I have did this on several cars, before or after a remap and it has always been a sensible power increase. It seems like that more km/miles the car has, it better gain after a de-cat.

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    Go for it I noticed a big difference when dpf and cat was removed well recommended

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    Hi Winnie...................ben been to see you yet

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    He is coming down in 2 weeks so will let you know mate

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    Regular Member Torque's Avatar
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    Quote Originally Posted by zafira View Post
    I did de-cat/dpf my vectra before I remap. And definitely gain performance. I have did this on several cars, before or after a remap and it has always been a sensible power increase. It seems like that more km/miles the car has, it better gain after a de-cat.
    Sounds good.
    You're on about standard remaps as well, not custom ones correct?
    I love the sound that comes through the exhaust on a diesel after a decat but I'd never even consider it if there was the possibility of losing power.

    The bloke that done my remap said he's seen it on too many occasions where people have decatted or fitted a custom exhaust and lost power on the RR if the car has a standard map on it. This is why I suppose I've been more persuaded not to take the risk. As I said before I've rang plenty of tuning specialists and heard an equal balance of mixed responses.

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    Regular Member zafira's Avatar
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    Quote Originally Posted by Torque View Post
    Sounds good.
    You're on about standard remaps as well, not custom ones correct?
    I love the sound that comes through the exhaust on a diesel after a decat but I'd never even consider it if there was the possibility of losing power.

    The bloke that done my remap said he's seen it on too many occasions where people have decatted or fitted a custom exhaust and lost power on the RR if the car has a standard map on it. This is why I suppose I've been more persuaded not to take the risk. As I said before I've rang plenty of tuning specialists and heard an equal balance of mixed responses.
    Now I have remapped my car. But I run it some months after dacat/dpf before I did the mapping. And its a reasonable different, the engine revs easier and get more torque all over.

    I have removed cat from:
    - Tree omega dti
    - Combo dti
    . Vectra dti

    and removed cat/dpf on:
    - zafira vdti
    - Vectra cdti

    and they are all the same. More power after. I am nut sure what happen with a custom exhaust, but removing the cat/dpf its no doubt.

    On vectra its easy. just cut the pipe between cat and dpf, smash thats inside and veld it back together.

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    I think people maybe getting their wires crossed if you remove the cat from a turbo'd car you will gain some torque and bhp with or without a remap. If you remove the cat from a none turbo car you will lose power without a remap because they need a backpressure in the exhaust to run properly.

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    Quote Originally Posted by zafira View Post
    Now I have remapped my car. But I run it some months after dacat/dpf before I did the mapping. And its a reasonable different, the engine revs easier and get more torque all over.

    I have removed cat from:
    - Tree omega dti
    - Combo dti
    . Vectra dti

    and removed cat/dpf on:
    - zafira vdti
    - Vectra cdti

    and they are all the same. More power after. I am nut sure what happen with a custom exhaust, but removing the cat/dpf its no doubt.

    On vectra its easy. just cut the pipe between cat and dpf, smash thats inside and veld it back together.
    hey matey , getting a 120 vec C if i remove the DPF n CAT what will happen EML wise ? want to be sure before i smash the middle out of mine bud !
    cheers

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    Regular Member winnie2457's Avatar
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    If your veccy has a dpf it will have to be a automatic hatchback, a signum or a estate veccy to have one

    If you open drivers door there is a black sticker on with axle weights etc on the bottom if it has a 0.50 it has a dpf

    I you smash the dpf off you will have to get a remap to stop the regen process this is the only way otherwise you will e burning loads o fuel and smoking like a steam train

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