A few weeks ago I noticed a rattling under my car. The outer shields came off the cat on the right driver's side (spot welds popped right off), and one of the spot welds popped off on the passenger side cat. The top shields hadn't slipped off the converter and was rattling between the converter and the undercarriage. I removed the left one and clamped down the outer side of the passenger side cat where the weld had broken and the rattling is no longer there.

I called MTI, whom I bought it from, and they suggested I run it like that. <img border="0" title="" alt="[Roll Eyes]" src="images/icons/rolleyes.gif" /> But, suggested I call The manufacturer if I wanted something done about it.

Well, I let it go a month or so, but now I'm also getting Converter codes thrown (TWC something or other) I think it was P0420 and my car is losing power at WOT. I'm also getting black smoke when I initially hit the throttle. My boost is also rising slower, but spikes higher... back at about 12 PSI, as if the back-pressure has increased. But, it does this erratically.

Does it sound like one or more converters may be blocking up, or do you think I am off base here?

I ordered an Off-road y-pipe so I can test it for sure. (That's the only way I know to eliminate that as a cause.) I guess exhaust shops likely have a way to check... but will their check tell for sure... or will they end up giving me an educated guess and not REALLY know without "fixing" it, only to find out that is not the real cause?

I still love the MAC headers themselves, but only minimally spot welding the shields seems unnecessarily.

I was going to try the off-road pipe for certain visits to the track anyway, so I won't have lost by trying that.

MAC is willing to look at the y-pipe. I guess I will see how they stand behind their product.

What do you guys think?

 

Am not familiar with Macs, so.. clue me in if needed. Why not replace the cats with a hi-flow race setup? Do F-Bodys have 1 or 2 main cats?

I run 2x 2.5" C&L SD's. Flow 450cfm each I believe, but need to check my notes. C&L has 3" also. Cost $89 each or so.

 

My guess is you've been getting them pretty hot, hotter than normal.

P0420 is a CAT efficiency code. You may have started to melt the first couple inches of the brick inside the converter. That will through the code, and increase the exhaust back pressure. That certainly is a good way to reduce power.

Cut those puppies off <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

Why are they there in the first place?? <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

 

put some cutouts on that thing.

 

Ya

 

OK... I guess it is a concensus. <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

I have to have SOMETHING for inspection though...

 

Heat shields are only if you park in tall grass. Dont feel bad about taking them off. Just dont park in tall grass. As far as the rest goes, yeah, your convertors are hosed. If your acceleration is sluggish then its probably the cats clogging up, ive actually seen them so bad that they've glowed red. Your local exhaust shop should easily be able to create your own removable cat setup - just a few 3 bolt flanges and the donut gaskets. How rich are you running? Thats a surefire way to kill them.
As far as how to test it - most times its an educated guess.. but keep in mind most of these guys see the same thing 10 times a day, so if they are ever wrong, its not often. My dad has worked and/or managed exhaust & brake type shops for the past 30 years, he can just put his hand over the exhaust pipe and tell you in a second.

 

Thanks, Jason... that's very helpful information.

The problen with custom off-road setups, I can't find a single shop that will touch the exhaust in any way. Thee won't even carry stuff like doughnuts and clamps that you can interchange. They weld all their stuff. He said the type of clamping they do is as firm as a weld... sorta like a cripmp that would have to be cut out just like a weld does. And don't DARE ask anyone to weld in a cutout! <img border="0" title="" alt="[Mad]" src="gr_images/icons/mad.gif" />

When people get caught running an illegal setup, the law goes back to whoever did the exhuast and the shop is prosecuted. A place I stopped at Friday where the people are cool and I thought I could at least get them to build me an off-road setup and then take it off the car and put the cat/y-pipe setup back on (so I could do the swap-out myself later) simply refused.

One of the guys told me their shop has been fined $5000 per incident about 5 times in the last twenty years.

The smog-cops have the exhaust shops running scared. <img border="0" title="" alt="[Sad]" src="gr_sad.gif" />

 

MelloYellow, give me a link on where you got your race cats.

Thanks, man.

 

Yo.. just read this.

C&L Cats
I have a true dual with 2.5" x2 C&L SD's.
Dunno if you want a single 3" ?

http://www.cnlperformance.com/cats.html
http://www.cnlperformance.com/index2.shtml
http://www.cnlperformance.com/graphics/25.jpg

Let us know how the change affects your boost!!
Ya, being too rich at 10:1 probably killed 'em.

<small>[ April 04, 2002, 08:28 PM: Message edited by: MelloYellow ]</small>

 

Sounds good, MelloYellow. Thanks.

I think I'll get that rather than have MAC replace the ones I got from them in a y-pipe.

If they flow better than aftermarket mufflers, how can you argue with that level of restriction?

 

I've had a set of Mac cats do the same thing. The "clamps" I used were the little aluminum window locks for a house window. They worked for a while but eventually I ended up removing the shields and ultimately the converters themselves. I have since replaced my off-road pipes with FLP cats (in the Mac y-pipe). Now, after about 5 or 6 months, the shields on the FLPs are doing the same thing. I tried to be legal but it's too damn expensive. I think I'm through with cats. I'm going to see about getting a "convertible" setup.

 

Has GWP given you any guidance with this problem? Hope you find the cure and let us know. <img border="0" title="" alt="[Cool]" src="gr_images/icons/cool.gif" />

 

Considering the Cats were just falling apart, is it possible they were just defective thru and thru?

The outer heat shields had come off on both sides.

 

Its possible, but I doubt it. There are just a couple little pissant welds holding the heat shields on. Shaking + heat = byebye heatshields