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Will I Need A Retune After Cahanging My Catalytic Converter ?

Tweaky

By Tweaky,
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Tweaky

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Posted

Just bought a Venom 500 series hi flow cat with a 100 CPSI flow for 3 inch exhaust system. I am running a Microtech Lt x12s ecu , will i need a retune once i fit the new catalytic converter ? At the moment it has a ceramic cat fitted to the exhaust system , which has had a few bumps & bruises !!! So i thought i would replace it with a stainless steal one , which will last longer & have better flow. Will the extra flow cause the fuel / air ratios to change ? :thanks:

Tweaky Collaborator

Tweaky

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Posted (edited)

no

flow speed wont be noticable

But if i'm going from 400 CPSI cat to a 100 CPSI cat flow sould be alot better ! If not what would be the point in changing cats then ?

Edited by Tweaky
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Moodles2 Grand Master

Moodles2

Posted
Posted

The point of changing the cat is to relieve backpressure, with a freeflowing cat the exhaust velocity is maintained (where it might have been slowed down when caught in the 400cpsi) which helps helps turbo response.

Tweaky Collaborator

Tweaky

Posted
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The point of changing the cat is to relieve backpressure, with a freeflowing cat the exhaust velocity is maintained (where it might have been slowed down when caught in the 400cpsi) which helps helps turbo response.

So once the new Hi flow cat is fitted & there is better flow , will that be enough to upset any current tune settings on the ecu ? Will the car have to go back to my tuner for any slight adjustments ? :thanks:

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ClutchBurndout-:( Grand Master

ClutchBurndout-:(

Posted
Posted (edited)

But if i'm going from 400 CPSI cat to a 100 CPSI cat flow sould be alot better ! If not what would be the point in changing cats then ?

are you expecting amazing things from changing cats? unless your running high numbers it doesn't really change much

ive tried more cats than an 80 year old chinese cook

Edited by Clutch
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Sunkist Grand Master

Sunkist

Posted
Posted

if anything

you would come on boost earlier, causing a lean of fuel in certain rev ranges.

but this would only happen if your tune was shit to begin with ie running TOOOO lean..

shouldnt be a problem, unless your fussed about 1 or 2 kw's..

Tweaky Collaborator

Tweaky

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O.k thanks guys , just wanted to make sure ! Better to be safe then sorry :nyaanyaa: Car is making the 290rwkw mark at the moment , the guy who sold me the cat recommend i get a tune after it is fitted. Thats why i'm double checking :thumbsup: The last tune was done 3 months ago & car is running great , anything i think the car would be running on the rich side.

Edited by Tweaky
  • 14 years later...
silviaz Experienced

silviaz

Posted
Posted

Does it make a difference in your turbo having a shorter life if you have a cat converter as it causes that back pressure versus less/no back pressure with a decat? (Not sure if this is accurate)

Also slightly different question if you went from a oem cat to a decat or vice versa will it require a tune? I heard if you change the dump pipe onwards it requires a tune?

GTSBoy Grand Master

GTSBoy

Posted
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20 minutes ago, silviaz said:

Does it make a difference in your turbo having a shorter life if you have a cat converter as it causes that back pressure versus less/no back pressure with a decat? (Not sure if this is accurate)

Not noticeably. Arguably, the catless turbo is going to work harder in a different direction, as it will spool up faster, go to higher speeds more easily.

30 minutes ago, silviaz said:

Also slightly different question if you went from a oem cat to a decat or vice versa will it require a tune? I heard if you change the dump pipe onwards it requires a tune?

Only if it was tuned in the original condition. If it was a stock tune, using the AFM before and after the cat/dump change, then no, no retune needed. If the car is running on a MAP sensor, then it might well benefit from a retune. It might even run a little dangerously without a retune, but it could quite easily be fine.

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silviaz Experienced

silviaz

Posted
Posted (edited)
3 hours ago, GTSBoy said:

Not noticeably. Arguably, the catless turbo is going to work harder in a different direction, as it will spool up faster, go to higher speeds more easily.

Only if it was tuned in the original condition. If it was a stock tune, using the AFM before and after the cat/dump change, then no, no retune needed. If the car is running on a MAP sensor, then it might well benefit from a retune. It might even run a little dangerously without a retune, but it could quite easily be fine.

Ah, to clarify if the car has already been tuned and has been modified and you want to go from a oem cat to a 100 cell or decat or vice versa.Are you saying that the car doesn't need to be tuned after a cat change if it's already been tuned?

Edited by silviaz
Murray_Calavera Mentor

Murray_Calavera

Posted
Posted
7 minutes ago, silviaz said:

Ah, to clarify if the car has already been tuned and has been modified and you want to go from a oem cat to a 100 cell or decat or vice versa.Are you saying that the car doesn't need to be tuned after a cat change if it's already been tuned?

Maybe?

If changing the cat to a higher flowing cat, caused the turbo to spool more quickly, and those areas of the map had not been tuned for the boost level it is now seeing, then yes you would need a re-tune. How dangerous it is running without the updated tune would depend on how far out the tune is with the now higher boost levels, how the engine protection has been setup, is the ECU compensating with a wideband sensor, is the boost control closed loop blah blah million other things...

But yeah having said that, I wouldn't be surprised if changing out the cat for a high flow, in say a full 3" exhaust, made no noticeable difference at all. 

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