CT03911

My car was off on performance and running warm. This condition had worsened over time but became very apparent at Watkin's Glen recently as cars I knew I used to outperform pulled on me and I drove another 2004 GT3 with low track miles. That car very obviously had more grunt. Like 10mph into the bus stop more.

I decided to gut the cats which should resolve the performance and probably temp issues both, but also to pull the front bumper and clean the radiators now too and install screens.

The chassis shop at Moroso (thanks Paul and Rick) got my car up today and we pulled the cats down, opened them up and removed what was left of the core. It clearly was blocking the exhaust a lot. Paul did a fantastic job of closing the cat up, the welded area is facing up so the cats from below look completely normal.

I have not driven it yet but in time the car will probably throw a check engine light and cat code. I will deal with that later. I am told no cats but normal OEM mufflers will pass noise at LRP. Hope so.

It really surprised me the amount of junk clogging between the radiators. I blow out the front ducts EVERY time I wash it. Plenty of garbage was still in there. The bumper removal was easy. Tomorrow Moroso will fabricate screens and we will get it all back together for a road test.

CT03911

To be a little clearer, when I started my car cold, I could hear some "exhaust rattle". It would go away about the time the engine rpm dropped as it warmed up, ie in maybe 30 seconds or one minute or so.

I have had the rattle since 4500 miles when I bought it. I now have 21,000. After the CPO purchase I asked the Pcar dealer about the rattle and we discussed the cats. They replaced the tips saying the welds were bad. Clearly, this did nothing. I asked for new cats and they declined saying it had been tracked.

Fast forward some years and the core was clearly getting banged around and hit with high temps. I had suspicions of course, but now it all makes so much more sense. I actually was going to do this last summer. Wish I had.

The core became what you see in the pictures today. After the car was started a while the rattle would go away (the core would, I figure, slide over into place, covering the exit pipe).

The more it formed into the size and shape of the actual exhaust pipe and further clogged up, the more my performance dropped off and the temps went up. This was quite subtle at first but seemed to accelerate last few events.

One shop told me it was like breathing through a straw. The motor was working hard and so temps went up while HP went down.

PAULUNM

Amazing to me you haven't had a CEL with the internals of the cats being in that condition.

Did you notice the extra power? Change to the loudness of the exhaust?

CT03911

I have been told there was no CEL because the car basically sees no street miles. At WOT it will not look for O2 sensor issues.

That's one piece of advice.

The other was my own wondering about how I could not get a CEL.

The core was not completely blocked. When it rattled about briefly and then seated itself I am wondering if it was effective (to a degree) in converting the exhaust. Enough to satisfy the O2 sensors anyways.

Reduced flow sure, but the O2 sensors don't look for that.

Anyways, I got a CEL last summer. Cleared it and it never came back.

I wonder how long it will take for it to come on now?

bobsan

That's exactly why you saw no CEL, because you where mainly WOT. It takes around 80 miles of partial throttle with defective CAT to trigger a CEL. The ECU looks at the 02 sensors four or five times over a given period and if it's not happy with the results it throws the light.

996FLT6

Damn that thing the core is so fubarred. How much that brick weigh? Talk about constipation. Mike

Gert

I have seen this before on a 996C4S and also no CEL.

911SLOW

Good job finding the problem, but gutted cats aren't good for flow.
Better to cut on their edges and just use a straight pipe.

The CEL will eventually come. You can use a pair of O2 extensions to minimize its appearances.

LVDell

Installing screens is a must. Good job doing that!

And like John says, you can use a set of 02 extenders to avoid any potential CEL. I ran a set on my last car when I ran the cat delete and got no CEL.

HiWind

Always amazed at what gets onto the rads and thru the grills! Did the clean out work?
Here are my before and after of the de-cat which dropped 8kg simple and easy and def better flow. Are you concerned re road-regs and emission testing? We don't have that (yet)

https://rennlist.com/forums/9343709-post1.html

bobsan

[IMG][/IMG]

[IMG][/IMG]


should look similar to this before melting, these are 100cell so half size of OEM part

bobsan

that quite impressive, getting CAT to that state and still running ok'ish

SH || NC

Wow. Is that dirt in the cat area?

kk2

Probably shavings from cutting the opening.

CT03911

quick answer to some questions: That was material from the cutting wheel. The cats are done and the front end radiators all cleaned out and buttoned back up. Moroso fabricated screens. Road test here in a few minutes. Pics coming soon. The weight savings was minimal. The cat internals don't weigh much. Not mine anyways :-)
I will say this, I vacuumed and brushed the radiators a lot and got them clean. Then I blew them out from the back forward. I was amazed at the pile of sand I blew out. Glad I did not skip that step.
I figured a straight pipe was better for flow. Not having a blockage will be better and the pipes are not straight so it would require a bit of work to just replace the cat with a pipe. I decided this was cost and performance effective enough for me.