Removing Clogged Rear Cats?

[duke16]

I had Meineke check out my cats to see whether or not they were clogged (I've been experiencing hesitation during acceleration and up hill), and they checked the temperatures in and out of each cat and got these numbers.

Front
378 in, 442 out
432 in, 460 out

Rear
310 in, 273 out
361 in, 303 out

So, apparently because the air is supposed to be hotter going out then coming in, the rears both need replacing. Well after looking at what he quoted me, I'd much rather just remove them all together.

I took a look at them and it looks like they simply bolt on. So I'm wondering if there is an aftermarket pipe that I can get to replace them? Or would I have to have something fabricated?

Also, if there isn't simply a bolt on replacement pipe section, I may go ahead and redo the exhaust all together. Right now, it's completely stock and I have TM headers with the KKM intake. So what would be the best option to compliment those two that isn't to loud during idle, but more throaty during throttle?

Thanks.

 

[wyochimneysweep]

i removed my rear cats and put on two thrust turbo mufflers. not to loud at idle and sounds pretty good when i get on it. i just unbolted the cats cut them off and welded pipe in place of them and then bolted it back up

 

[Cobraguy]

You need to worry about the smog cops. Fortune410 says he has no problems with the Colorado inspections with them removed. Here in AZ, we do. In fact, Federal Law states it's illegal to tamper with them, so I guess that pretty well sums it up for everywhere. But with that being said, I asked an inspector here about removing them since they are after the rear O2 sensors. Can't do it. No way. BUT! He said he wouldn't give it a second look as long as the primary cats were on the car.

 

[duke16]

Well as far as I know, in N.C, only the ODB-II scan is done for emissions. What I think I may do for now is just hollow out the cats. Trouble is going to be unbolting them, it's pretty rusty under there.

 

[duke16]

Actually, after doing a bit of reading I'm not sure hollowing them out is the best approuch.

However, hollowing out a catalytic converter will cause resonance problems. The symptom is most often seen as a hesitation, popping, or backfire at or about 3,200-3,500 RPM. Upon hard acceleration, the engine will appear to cut out for a split second as RPMs drop and a split second later recover and continue past 3,200-3,500 RPM. Additional symptoms are a loud and continual popping sound when the vehicle is allowed to decelerate under load and a whooshing sound that is delayed from or following the engine speed. This is due to the open chamber within the hollowed out catalytic converter case. It loads up and releases pressure in the exhaust system that acts almost as a capacitor. The open chamber allows the formation of standing waves within the chamber which reflects back toward the engine and causes the hesitation and miss in the RPM range.
The symptoms become more pronounced as the exhaust system is made freer flowing, meaning that hollowing out a cat with the stock exhaust may cause mild annoyance, while it becomes a serious problem when a header and performance exhaust system are installed, mimicking a ignition miss or backfire. This is probably the best reason not to hollow out a catalytic converter.

http://www.isuzuperformance.com/isupage/tech/exhaust.html

Has anyone hollowed out their rears and can comment on this?

 

[Cobraguy]

I don't believe in gutting cats. But I'm sure that article is reference to gutting the main cat on a vehicle. Not the secondary like you're talking about.

 

[Ray Lobato]

Let me state this before I close this thread.
It is managements position that we do not endorse doing illegal activities.
Gutting out your catalytic converters or removing them is not a legal activity, and prohibited on this website.

Thread closed.