remove first or second catt?
 

Hello! it already knows what the catt is important in removing pollution?
it is better decatt headers and retain second catt? or retain OEM headers and eliminate the second catt?

Umm... why?

For power, from what I read on this forum, removing the primary cat (in the header) makes a lot more power than removing the secondary cat.

But removing 2nd one might be much cheaper/simpler.

Why not remove both?!

How about aftermarket cats for both?

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Header one will get you engine codes without a tune.
Second one will be less benefit, but will be cheaper.
I'd say, go header or go home, tho.

Catless Header + Catless Front Pipe + Tune = 1st for gains = Very Smelly Car

Catless Header + Catted Front Pipe + Tune = 2nd for gains = Car Will Still smell sometimes especially in traffic and on start up, just not as much

Catted Header + Catless Front Pipe + Tune = 3rd for gains = Car won't smell, only on start up while it warms up the cat in header.

Basically the cat in the header is the main cat and most restrictive cat so removing it will create most gains but also create the most smell. Hope that helps you :)

perfect! Thank you very much to all of you
I thought the first cat is there only while the second cat is heated. I thought it was less effective to trap pollution and that the truly important was the second cat cat

High flow cats are an option too.

I'm catless and I don't notice much smell ever. Its not as strong as say a civic anyways. On e85 there really is no smell.

I believe that in most cars, the second cat is there while the first cat is warming up. The secondary cat is less effective and less restrictive. So, as far as solution goes, the first/primary cat does most of the work and is also the most restrictive and thus is the first one most people will remove (via a cat-less header in our cars).

You can definitely tell from the smell when the primary cat is removed (nose-dependent :)

When second cat is heated up, it cleans up well enough (many had passed MOT checks if their local rules aren't anal about mods like in CA), even if it's only one. Unfortunately newest smog/exhaust standarts measure also from cold starts, hence extra 1st cat is placed much closer to cylinders, where it happens to be robbing lot of performance, especially for NA. But it heats up to working temps there quicker. From all of this I wouldn't say, that 1st cat does most of work .. it just starts working sooner.

Get a catless header + tune. End of story. Life Changed.