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Old 10-04-2009, 05:14 PM   #1
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Exclamation Cat or not to Cat...

I'm considering removing my (apparently plugged) cat converter. Don't really want to replace... just straight pipe it. I've heard EVERYTHING from "the computer will compensate and run a little rich"... to ..."it'll run lean and you'll burn your valves up..."

OK experts.... what's the skinny? What's the real answer so I can make a decision.
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Old 10-04-2009, 05:17 PM   #2
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This is your first post? Don't you think it might be appropriate to describe your vehicle and any mods?

If you like polluting, pull the cat. If you hug trees, get a new one.

Will you blow your junk up w/o a cat? Maybe. Depends on tune/mods.
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Old 10-04-2009, 06:31 PM   #3
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2001 Miata MX-5. Stock for the most part. Member here a long time ago. Minor computer issues. Mods...? not really. K&N filter up front. 40 series Flowmaster muffler in the back. Custom wheels & tires.
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Old 10-04-2009, 06:37 PM   #4
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depends on if you have to pass emissions testing in <LOCATION NOT FOUND>
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Old 10-04-2009, 06:40 PM   #5
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No emissions testing here.
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Old 10-04-2009, 06:45 PM   #6
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Mechanically it will be fine without a cat, but it will sound like crap. A resonator, or better yet a turbo, seems to kill the raspyness that results from not having a cat.
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Old 10-04-2009, 06:48 PM   #7
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Thx. The Flowmaster has a nice throaty sound. Not like I just left a high school parking lot from a "buzzer". Should produce a deeper tone w/out the Cat. My concern was the valves. Didn't want to burn them up if the computer leans it out.
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Old 10-04-2009, 07:10 PM   #8
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Meow....
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Old 10-04-2009, 07:30 PM   #9
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Facts:

1: Removing the catalytic converter (or otherwise decreasing restriction in the exhaust) will very slightly increase VE. In theory, any such improvement in breathing will be reflected as an increase in measurable airflow at the MAF sensor, so there should be no significant change in fuel mixture, either open-loop or closed-loop. (If you were running MAP-based, then you'd be a little lean.)

2: It will cause your ECU to throw a CEL for P042(x).

3: Diet Dr. Pepper does not taste like regular Dr. Pepper.

4: I can believe it's not butter. The consistency is considerably different, especially when not refrigerated.
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Old 10-04-2009, 07:35 PM   #10
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I getting rid of the Cat after my build.
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Old 10-04-2009, 07:46 PM   #11
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Most (all?) SMs run w/o cat. No problems.
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Old 10-04-2009, 07:51 PM   #12
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I have no quicker spool on the downipe vs the full exhaust with a 3" cat.

It sounds really cool on the DP though, just makes me a little dizzy.
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Old 10-04-2009, 08:46 PM   #13
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where do you live should be the only question
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Old 10-05-2009, 12:17 AM   #14
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dont run a cat for performance

run it for the children.
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Old 10-05-2009, 12:40 AM   #15
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Quote:
Originally Posted by Joe Perez View Post
3: Diet Dr. Pepper does not taste like regular Dr. Pepper.
I approve of this point.

Also, it's "Dr Pepper." No period after the Dr. Oddly, Mr Pibb is the same, with the no period thing.

Fun fact for the day.

EDIT: Oh, I guess for relevance I should say that I am running a cat on my 3" exhaust, but the car has never run on it (waiting on parts until the heat death of the universe), so I don't know what difference it makes. You can see directly through a metal core, and it's huge, so I don't see it making any appreciable difference.
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Old 10-05-2009, 12:56 AM   #16
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fun fact:
Dr. Pepper is for homosexuals.
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Old 10-05-2009, 01:22 AM   #17
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Quote:
Originally Posted by hustler View Post
fun fact:
hustler is for homosexuals.
fixed
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