[kabukiman]

So I have been wondering

There is a cat bolted straight to the exhaust manifold on the 2.0L engine correct?  underneath the car, I believe I see another cat?

2 cats?  Then after that I believe a tiny resonator and that huge muffler

I am looking to alter my exhaust some.  I feel perhaps it is a little restrictive (especially if it has two cats) and am looking to hear a little exhaust when I give it a kick.  The stock system is so quiet, when it's warmed up I can hardly hear it at all, the fuel pump is louder.

So I was thinking perhaps removing one cat, putting a new resonator in the middle and a smaller muffler at the rear.

Anybody modified the exhaust system on an i30 here?

[Doggie 1]

Is the individual shown in your avatar the one responsible for all this cruelty to cats that you speak of? 

[2i30s]

don't remove any of the cats on your car,it will over heat and run lean.  i replaced my hatch exhaust with a sport system that's mandrel bent,high flow resonator and high flow muffler,all 2.5 inch.  you could save some money by just replacing the large rear muffler with a sports one and removing the small front muffler. 
 CAUTION.....DO NOT REMOVE ANY OF YOUR CATALETIC CONVERTERS. 

[Phil №❶]

don't remove any of the cats on your car,it will over heat and run lean. 

Can you explain this please 

[TazManiac]

I also cannot understand this. The process of mixing air with fuel is done well before it reaches the cat. The cat is designed to react with (catalyze) the engine gasses to remove the harmful ones. To my understanding this has nothing to do with the richness of fuel:air ratio.

[Phil №❶]

I am aware of inbuilt oxygen sensors, which can send info to the ecu which could alter the mixture settings for the engine and make it run lean. I just wanted to know if that's the reason or not. However, one would think that if there is a wire connection to the cat for thisd purpose, you wouldn't cut off the cat and leave a wire hanging, it's obvious it's meant to do something. 

[kabukiman]

there may in fact be a sensor in the second cat, in which case I'd leave it in place

Everything after that is fair game I guess

[Michael T]

That second sensor is there for the sole reason to make sure your cats are working properly.

On most cars, if you remove the cats and don't position the sensor high enough out of the unrestricted gas stream the car will think the cats are bad, because of the excessive temperatures and will run rich. Been there done that. You either need to tune your car for it to turn off the engine light or put a few washers between the sensor and the pipe.

[2i30s]

don't remove any of the cats on your car,it will over heat and run lean. 

Can you explain this please 

sorry for the very late reply.    I'm not 100% sure why the car runs hot but I've learnt from prior misstakes not to remove the cats.  on my last car,a 5.0 tickford enhanced NC fairlane,i stupidly removed the cats and replaced the exhaust from the extractors back to the diff with 3" tube for a horsepower gain and caused the car to yes as mentioned above,run super rich but also run very hot.    after refitting the original exhaust back to the car [with cats ] it ran cool again. i asked the exhaust guy that supplied the 3" exhaust tube i used and he said never remove your cats,unless you tune your engine to run without them. 

[Phil №❶]

Things may have changed with newer model cars, but my old car had a O₂ sensor and no sensors in the cat itself. Reading the workshop manual it said that after warm up the sensor produced a small voltage 1.0 to 1.5 I think, which told the ecu how much oxygen was in the exhaust and the ecu modified the mixture accordingly (for anti pollution reasons, not performance), so if you knew what the ecu was expecting under normal circumstances for your vehicle and reproduced that electronically, wouldn't that enable you to run without cats. 

[kabukiman]

Things may have changed with newer model cars, but my old car had a O₂ sensor and no sensors in the cat itself. Reading the workshop manual it said that after warm up the sensor produced a small voltage 1.0 to 1.5 I think, which told the ecu how much oxygen was in the exhaust and the ecu modified the mixture accordingly (for anti pollution reasons, not performance), so if you knew what the ecu was expecting under normal circumstances for your vehicle and reproduced that electronically, wouldn't that enable you to run without cats. 

yes people make o2 sensor bullshitters, or that's what I cal them.

With my Fiesta anyway I had the option of a little plastic box which connected to the o2 sensor in the exhaust and fed it fake readings so you could race the engine with just the headers or a straight pipe without ecu modification

[GrandMasterPaps]

I recently did my Exhaust, absolutely love it. 2inch pipe, duel tip, sounds like a beast goes like a little pocket rocket 

[kabukiman]

I recently did my Exhaust, absolutely love it. 2inch pipe, duel tip, sounds like a beast goes like a little pocket rocket 

the 2.0L beta in these i30s have a really nice induction note so I was thinking a slightly louder nicely tuned exhaust would benefit it greatly