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ElantraClub - For Elantra Owners and Enthusiasts _ Power Zone _ cat delete?

Posted by: Tyler Aug 14 2012, 12:49 AM

Iv noticed a lot of you guys put just a little something on for exhaust just to open it up and let the car breathe a bit better but it seems everyone is doing cat back. Am I the only one that wants to take out the cat and go strait back from the headers to a muffler?

Posted by: silet Aug 14 2012, 06:50 AM

Deleting a catalytic converter these days causes emissions problems with car computers being so finicky.

On the other hand, you have to know what you're doing when deleting a cat. You have to have a purpose and goal. If your goal is more horsepower, then removing the cat alone will do nothing towards that objective.

Modern catalytic converters do not restrict flow as much as people think. The exhaust resonator and muffler do a lot more to restrict flow and the intake resonator too.

So in conclusion, if you want more HP removing the cat is not the way to go...

Posted by: Bobzilla Aug 14 2012, 08:45 AM

Agreed. Even deleting the cat and replacing with a header (singular, we only have one, not multiple headers) you can expect to gain about 2-3hp as has been shown on multiple dyno's over the years. Biggest improvement with the XD chassis in regard to exhaust is the muffler. The exhaust pipe feeding the muffler is ~2" id. The outlet of the muffler is under 1-7/8" ID. Removing the muffler frees up more power than hacking off your cat and dealing with a CEL on for years to come and not being able to pass emissions in your state (if required)

Posted by: Tyler Aug 14 2012, 11:48 AM

Oh ok. And no I don't have emission testing. And I didn't realize there was such a small amount of gain with cutting it off.

Also iv read there is two cats on our cars is this correct?

Posted by: silet Aug 14 2012, 02:02 PM

yes, two cats.

Posted by: only1db Aug 14 2012, 03:28 PM

yes the first cat i welded (casted) into the exhaust manifold while the other is down stream...the 2nd cat you can remove without any ill effect or cel.

Posted by: korea_senpai Aug 14 2012, 06:32 PM

Are there not 2 O2 sensors?

Posted by: bhorste Aug 14 2012, 06:36 PM

QUOTE (korea_senpai @ Aug 14 2012, 07:32 PM) *
Are there not 2 O2 sensors?


There are... the first is before the first cat and the second is after (or between cats).

Posted by: korea_senpai Aug 14 2012, 06:45 PM

I don't see a problem with deleting the cat, shouldn't throw a CEL but the only thing its going to do is probably make your car annoyingly louder. I deleted my catalytic converter on my RX7 and its obnoxiously loud.

Posted by: bhorste Aug 14 2012, 08:12 PM

QUOTE (korea_senpai @ Aug 14 2012, 07:45 PM) *
I don't see a problem with deleting the cat, shouldn't throw a CEL but the only thing its going to do is probably make your car annoyingly louder. I deleted my catalytic converter on my RX7 and its obnoxiously loud.


Wankels are notoriously loud anyway. I have a friend that had a 2nd gen RX7 (I want to say ~'89) and it was pretty loud. Granted, it had a rebuilt engine and probably not much in the way of emissions control, but it was loud. I doubt removing the 2nd cat on one of our cars would really add that much extra noise, since you've still got a resonator and the muffler after it, plus a couple of bends. What it *will* do is make it more likely that you won't pass emissions (if required) and it might affect your 2nd 02 sensor readings.

Posted by: korea_senpai Aug 14 2012, 08:39 PM

So we're talking about deleting one or both?

Posted by: Tyler Aug 14 2012, 11:53 PM

I was considering removing both the cats and resonator to lesson the restriction. But if it does make that much difference ill leave the first so I don't have to look at the cel lol

Posted by: winc Aug 15 2012, 01:48 AM

Deleting your catalytic converter WILL cause a CEL as it will make your oxygen sensor readings messed up, which will then cause your performance to be poorer and give you horrible fuel economy. They are crucial integral components for telling how much fuel gets fed to your engine.

The purpose of your first oxygen sensor is to tell the computer how much unburned fuel is coming out the exhaust... the second one tells how the converter is performing, both of which will effectively control your air/fuel ratio and advance or retard spark timing accordingly. Without the converters or oxygen sensors, it basically detunes your engine into a gas-sucking pig that runs like crap and drives even worse. Oh, that and a nice yellow warning light shining in your face while you drive it.


Posted by: silet Aug 15 2012, 07:21 AM

QUOTE (Tyler @ Aug 15 2012, 12:53 AM) *
I was considering removing both the cats and resonator to lesson the restriction. But if it does make that much difference ill leave the first so I don't have to look at the cel lol


Tyler, your are not going to have a big improvement, even if you get both cats out. I can guarantee you that if do remove them, I would be faster at the quarter mile with my 05. And when your ECU decides it had enough, a moped will beat down the drag strip...

Posted by: Tyler Aug 15 2012, 05:04 PM

Lol I sure am I glad I brought this up otherwise I woulda screwed myself for sure

Posted by: korea_senpai Aug 15 2012, 07:00 PM

QUOTE (winc @ Aug 15 2012, 02:48 AM) *
Deleting your catalytic converter WILL cause a CEL as it will make your oxygen sensor readings messed up, which will then cause your performance to be poorer and give you horrible fuel economy. They are crucial integral components for telling how much fuel gets fed to your engine.

The purpose of your first oxygen sensor is to tell the computer how much unburned fuel is coming out the exhaust... the second one tells how the converter is performing, both of which will effectively control your air/fuel ratio and advance or retard spark timing accordingly. Without the converters or oxygen sensors, it basically detunes your engine into a gas-sucking pig that runs like crap and drives even worse. Oh, that and a nice yellow warning light shining in your face while you drive it.


I'll totally buy this for a $1. ^knows his stuff. Total consensus please don't do it.

Posted by: RyanLJS Feb 25 2015, 06:33 PM

So I will have to replace my cat this summer even tho the car is 5 years old as the flanges have rusted away and literally metal is flaking off.. Depending on where the 2nd sensor is, say if its inbetween the 2 and you remove the 2nd cat will that throw a cel? As it would be a lot cheaper to add a section of pipe than buying another cat

Posted by: J2Elantra Feb 25 2015, 07:36 PM

The 2nd cat can be removed with no cel. Also saves over 10lbs.
http://www.elantraclub.com/forum/index.php?showtopic=35370&st=12&start=12

Posted by: kevinatfms Feb 27 2015, 11:39 AM

Remove everything from the secondary catalytic converter back and replace with 2 1/4" piping and a good turbo style muffler.

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