Miata Mailing List: May 1996, Message #5
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   From: Michael Garozzo 
Subject: Re: My Now Empty Cat
   Date: Wed, 1 May 1996 15:59:59 -0400

Here in PA I believe you would have problems passing state insp. emission 
control.  I recall reading that the engine is designed to operate 
with the back pressure of the exhaust system and that running without a 
cat will cause some problems.  FWIW.

Mike
Del Val Miata Club
91 Red B



On Mon, 29 Apr 1996, Benny wrote:

> Although I personally have no experience with hollowing out cats, I have
> been told that putting a straight pipe inside the cat with isulation
> around the pipe will not only improve performance but also help get rid of
> the annoying rattling noise (which the CHP is very good at hearing). Lemme
> know if this works.
> 
> P.S.- Next time you hollow out a cat, use a drill and wiggle it around.
> The cermaic breaks up into several pieces and you can get it done in about
> 2 minutes (although it DOES eat up your drill bit).
> 
>  On Mon, 29 Apr 1996, Seth Hamilton wrote:
> 
> > Well.. I decided I would just empty the cat out.. after undoing four very tight
> > bolts I proceded with a long chissel and hammer to knock the remainder of my cat
> > brick out (it was broken and rattling). 
> > 
> > There is more power... its actually rather noticeable at high revs and the car 
> > is more responsive (as far as the gas pedal goes) at 100mph+. However I think
> > it may have less torque now... though it still seems to lurch into action when I 
> > ask it to quite well.
> > 
> > Also, I had a serious wandering idle problem before I emptied that cat. It would wander
> > down to 200-250 then go up to a 1000-1050 then settle at 750-800. Now it doesn't wander
> > at all, and it idles smoother. The brick in the cat wasn't slightly dirty or plugged, it
> > was in excellent shape appart from a few chucklets floating about in it. 
> > 
> > Downers... the car smells a little different... but it doesn't smell like a rotten egg (I
> > was worried it might). I also have a free flow exhaust (trust) and now aswell as having
> > a deep growling sound, it now has a high raspy sound (which is produced by that cat can).
> > 
> > I think the can vibrates and causes the noise... but I don't want to get rid of the can
> > because it looks legal... any ideas of how one might silence the cat can? (btw: the car
> > isn't much louder... well not excessively louder anyway). Oh yeah... the car sounds
> > normal when its just cruising at an rmp (be it 3, 4, 5 thousand), the annoying noise only
> > occurs when the gas is down.
> > 
> > 							Seth.
> > 
> > 
> 
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