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The mkiv Supra Owners Club

What cat do you need to keep??


Jim_1979
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Just double decatted the car and fitted a cat back exhaust. Curious as to what one of the cats you need to put back on for the MOT? The larger one (underneath the car), or the smaller one? (closer to the engine)

 

 

Thanks in advance!

 

I kept the smaller one in the car and it passed, think it is also easier to remove the longer one.

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Yeah.. it would be easier to re-fit the longer one as it's miles easier to get to the bolts on it.

 

But if you re-fit either should it pass emissions testing?

 

Couldnt tell you mate, i failed full decated and scraped a pass with the front one in so think it would be a close call.

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Catalysts increase the exhust temperature by an exothermic reaction inside them. There is a specific exhaust gas temperature where the catalyst starts to 'light off' and begin converting the nasty gasses, and also creating more heat.

 

The front cat is a close coupled cat, called the 'starter' cat, that gets the exaust gas heated up quickly for the second cat during cold starts (i.e. its there to get the main second cat working faster).

 

Doing an MOT emissions test won't need this starter cat as the exhaust gas will already be up to temperature.

 

So...... to cut a long story short, just refit the main second cat, and make sure the car has been for a good blast prior to the emissions test to get the exhaust nice and hot!!

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