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Discussion Starter · #1 ·
I'm re fitting my CAT in a few weeks for MOT time.

With the usual 400/400 mods but set up to run with de-cat, will running a cat screw up any AFR and damage my engine?
 

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I think the usual advice is to not use boost when the Cat is on, just in case. Some places will fit the cat, MOT the car and then remove it for you all in one morning. ;)
 

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Discussion Starter · #3 ·
I think the usual advice is to not use boost when the Cat is on, just in case. Some places will fit the cat, MOT the car and then remove it for you all in one morning. ;)
Yeah i was going to take it easy when fitted. Was just wondering exactly how it would effect things and why?
 

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Generally the cat restricts the exhaust flow, which I believe tends to make the car run richer. This isn't normally a a problem but it causes issues if you run too rich, then the additional petrol in the cylinder can cause bore wash etc.
 

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The amount of timing and boost you can run with a stock CAT installed is much lower. So if the car has been mapped without it in, you will more than likey struggle to reach the same boost level as before, and the engine will most likely be knocking slightly, so the ECU will pull timing.
 

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Just take it steady with the cat fitted & whip it off again as soon as poss. Shouldn't do any harm in the short term (didn't to ours ;))
 
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