Stock Catalytic Converter Design

[whalenlg]

In 2020 I had to register my 951 in CA and it failed miserably. Replaced plugs, coil, plug wires, rotor, O2 sensor. Still failed.
Swapped OEM (original? 215k miles?) Cat with a Walker 81128. Passed with big margins.
Need to make sure that any new cat has an Executive Order # that is up to date with the CA website
https://ssl.arb.ca.gov/AftermarketParts/catalysts
and that the test station can see the EO # on the cat to verify it.

[Tom]

The more power your motor wants to make, the more effect the cat will have. The first time I tried a test pipe, my 2.5L motor was stock with APE chips. I remember being surprised that I could feel a real difference. How much? I don't know for sure, but I'd guestimate 10 hp? With a VR MAF and K27, I'd expect that number to be higher still. I'd also mention that --in my opinion-- the DEC cat appears pretty cheaply made and the active cat section is pretty small. It looks to me to be designed to just barely meet the EPA's 25k mile requirement on a bone stock car. If you ran it hard on a 300+ hp motor, I honestly don't know how long it would last, but I'm guessing not very long... That said, I don't really know of a better option for a full-time cat, other than maybe getting a bigger, better-built cat from someplace like Magnaflow and welding it in yourself.

[Tom]

In 2020 I had to register my 951 in CA and it failed miserably. Replaced plugs, coil, plug wires, rotor, O2 sensor. Still failed.
Swapped OEM (original? 215k miles?) Cat with a Walker 81128. Passed with big margins.
Need to make sure that any new cat has an Executive Order # that is up to date with the CA website
https://ssl.arb.ca.gov/AftermarketParts/catalysts
and that the test station can see the EO # on the cat to verify it.

Speaking of California EO numbers, I once had a smog tech try to shake me down (I believe) because the 951 was not listed among the cars on the EO for my DEC cat. He pulled up the EO on his computer and showed me that the 951 was not listed, and then started hinting about getting paid to overlook it. I called DEC and they pointed me to "ET Blast 27984" linked below. In relevant part it says:

Note: Until further notice, it is not necessary to check the specific vehicle application for non-OBDII equipped vehicles. In these cases, technicians must verify the catalytic converter(s) is equipped with an EO number and that the converter(s) appears to be properly installed. For OBDII equipped vehicles, technicians must check the vehicle specific application.

That particular smog guy got busted eventually, but I'm sure there are others out there still playing the same game, so worth bringing a copy of the 'blast' with you, and even 'offering' to call the Bureau of Automotive Repair if a tech needs further 'clarification.'

https://www.bar.ca.gov/services/EtBlast ... eKey=27984

[Doyle623]

Speaking of catalytic converter design, I have two stock cats here and one does not have the 2-bolt flange that connects to the wastegate pipe (circled). Did Porsche make two versions of these with different flanges?

68219824953__459F8126-6C19-49A8-9AB5-B213D4D9FB6C.jpg (102.96 KiB) Viewed 722 times

[Doyle623]

Update, I was able to confirm that the previous owner cut off the flange...so they should all have this two bolt flange attached.

[Tom]

Update, I was able to confirm that the previous owner cut off the flange...so they should all have this two bolt flange attached.

Sorry, I missed this question early. There were in fact two different types of flanges. On early cars, like my '86, it came from the factory with a small v-type clamp as shown in the first picture below. Both sides of the joint had a bell mouth that butted together around the donut gasket. Most test pipes were set up for the football-shaped flange, however, so a lot of people ended up cutting the bell-mouth off the wastegate dump tube so they could use it with the newer style cat/test pipes....

944 early clamp.jpg (24.09 KiB) Viewed 710 times

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[Doyle623]

Wow, thanks Tom, I did not know these existed. I checked various dealer sites and are NLA, but Ian at 944Online has them for $103. Hopefully I can find one second hand, since I want to pop this cat pipe on and try it out (the one with the flange has been gutted).