Stock Catalytic Converter Design

[Doyle623]

This is a duplicate post from over on RL, but thought I would also check here. I was just looking inside my factory exhaust pipe and noticed that the main catalytic converter was a straight through design (with mesh only around the outside), while the small wastegate pipe had a "mesh" design similar to current cats that I see online. The small pipe seen in the back of the first picture is the other side (front edge) of the catalytic converter section.

Am I missing a portion of the mesh in the main cat or were they designed this way, with mesh only around the outside of the catalytic section?

IMG_3947.jpg (23.46 KiB) Viewed 1027 times

IMG_3948.jpg (29.66 KiB) Viewed 1027 times

[Tom]

I have my old factory converter somewhere and can take a look. Can you see that just looking down the flange pipes, or did you have to snake some kind of borescope camera down there? Sure seems like a hole down the center of the mesh would defeat the purpose, but I'm no emissions engineer....

[Doyle623]

Hi Tom, you only need to shine a flashlight down through from the exhaust side. No Borescope needed. I agree, so I'm thinking my mesh blew out at some point.

[Tom]

Ok, I'll look today and report back....

[Tom]

My apologies, I couldn't find my old cat and now vaguely remember giving it away when I moved a few years ago. I'd bet a nickel someone smashed out the center with a pipe/dowel to make yours flow better -- someone who doesn't live in California that is....

[painenneck]

Stock 87 944 NA

[Doyle623]

Thanks for the feedback. Painenneck's pic confirms I'm missing the screen/honeycomb bits. I've had the car since 2000 and know the previous owner going back to '91. Didn't know of the cat being hollowed out, but apparently it was.

[Doyle623]

I found a lower mileage (~25k) catalytic converter that looks nearly new on the outside, but was wondering if the insides of the catalytic converters age over time (become brittle, crumble, etc.), or if it is simply composed of precious metals in a screen that should still be ok. I know that cats restrict flow, but I'm looking to reduce smell and want a simple stock-ish swap. I current have a 2.5" B&B exhaust, but it is catless and is rubbing my car on right hand turns (and driving me crazy).

Any thoughts on installing a older, low mileage stock cat?

[Tom]

I helped a friend pass CA smog once. He is an original owner of an '88 951S, and had removed his OEM cat many years ago when he tracked the car on the East Coast. Now in CA, he needed to get the car smogged, and I encouraged him to use my nearly-new DEC aftermarket cat for the test, since his was over 30 years old. He argued it would be fine because it had maybe 20 or 30k miles on it total. The smog tech was great, but nothing we did would get all three under the limit. The next day we put the DEC cat on, and the car passed way under all the limits. It's a sample size of 1, but supports the notion that age plays a factor and not just miles.

[Doyle623]

Tom, thanks for the input. Do you normally run your car with the cat installed or do you only install it for passing smog? I'm wondering how bad the DEC cat affects performance, although performance is no longer paramount for me.