S3 8l Catalytic converter

[86fran]

I have been reading up on exhaust systems for my S3 and need some advice.

I have a full stainless exhaust from the turbo back that was on my car when I bought it. On closer inspection it would seem that this does not have a catalytic convertor on it and I am need one for it to pass an MOT in September.

I have spoken with a local exhaust shop and they can weld in either a 400, 200 or 100 cell catalytic convertor, but I am unsure which one to go for. would the 200 cell be a good compromise? Or should I play it safe and go for the normal 400 cell one?

 

[Squirrelofdoom]

I'm in the same position. Previous owner cut out my cats but left the manifolds there so I can mount some more in. Looking for some OEM S3 cats to put back in

 

[aragorn]

200 cell should be fine.

100 will struggle to pass an MOT, and 400 is standard restrictiveness.

 

[Squirrelofdoom]

on the S3 as standard, you know it has the two CATs in there....are these both 400 cell then? Or are they both 200, adding up to 400? (not sure how these things work) Do people ever just weld in a single larger CAT?

 

[aragorn]

they're both 400.

Most aftermarket large bore downpipes do away with the Y arrangement that feeds the two cats, and would just run a single sport cat.

 

[Squirrelofdoom]

cool, cheers aragorn. Will be trying to get a standard OEM pair of CATs, not looking to shell out for performance exhaust

 

[<tuffty/>]

they use 2 x cats on an S3 for a couple of reasons... the cats are smallish sit either side of the prop to allow for the room thats there and to maintain ground clearance... 2 x cats also present a larger surface area due to the increase in exhaust gasses from a more powerful engine...

A single 250hp rated cat is larger than the 2 x cats the S3 has... the LCR uses the same DP/cat setup

<tuffty/>

 

[Squirrelofdoom]

Cheers Tuffty, should be able to grab some OEM ones from somewhere. I think i'm looking at about £200 for the CATs with sensor

 

[s3dave]

Ive got a 200 cell cat and it sails through the emissions every year, even asked if it was close and they so no, well within the limits