Catalytic converter tip (after muffler)

[blak88]

I recently acquired an 88 911 but failed smog most likely due to a catalytic converter issue.

The car is running B&B headers and exhaust with the catalytic converter bolted on the end of the exhaust.

Anybody have experience with these or do I have to put back the stock headers and exhaust every time I need to smog the car?

If the cat tips are legit, what are the chances I can borrow one from someone in Socal so I could pass smog?

Thanks in advance.

[Justin@Athens]

I have never heard of anything like this...pics? Who makes it? Most likely not real engineering.

[Bob Kontak]

I did a google search and they have cats that hook on to the end of the headers (or SSI's) but I can't picture how you would hook cats on the end of the muffler. Picture?

Suspect there is not enough heat to engage the catalyst.

[Quicksilver]

Having the CAT after the muffler isn't going to work. The exhaust going into the CAT needs to be hot and the CAT then heats it more through its catalytic reaction. It uses the heat/catalytic reaction to burn off the hydrocarbons.

The solution is to run really short dual cats right after the headers into a Magnaflow 11385. I believe that if you search that Moses and/or Jack Olsen ran that setup.

[Flat Six]

Originally Posted by Bob Kontak

I did a google search and they have cats that hook on to the end of the headers (or SSI's) but I can't picture how you would hook cats on the end of the muffler. Picture?

Suspect there is not enough heat to engage the catalyst.

And depending on how knowledgeable and/or strict your smog test station is, you'd fail the visual inspection anyway . . .

[blak88]

Surprisingly i passed visual at 2 different places.

First time it just failed the 25mph nox. Switched back to stock chip to see if that was the problem but then it just failed the 15mph.

Third time I switched back to the performance chip because it was giving me better number but this time drove it for 35 mins to make sure it was hot enough but failed both 15 and 25 mph.

This is where I determined that the cat was pretty much done.

[Quicksilver]

Originally Posted by blak88

. . .
First time it just failed the 25mph nox. Switched back to stock chip to see if that was the problem but then it just failed the 15mph.
. . .

NOX levels is partly controlled by the combustion pressure so there is a California specific jumper for that. One of the brown wires from the DME is connected to ground which is the "California emissions option". It causes the timing to be retarded by 4 degrees which reduces combustion pressure. If that wire isn't connected to ground then hook it up. If it is hooked up then disconnect it after smog for more power.
NOTE!!! There is more then one brown wire on the DME. You can do some research on this board to find out which one it is. (#8 comes to mind but I am just guessing from memory so check!!!)

Originally Posted by blak88

. . .
Anybody have experience with these or do I have to put back the stock headers and exhaust every time I need to smog the car?
. . .

BTW - The B&B headers won't pass the visual so you will need to swap the exhaust anyway.

I run a B&B setup and I swap it out for the stock system every two years. Because I use copper plated nuts, copper antiseize and the fact that the nuts aren't allowed to set for years means I don't have exhaust stud issues.
But...
The stock exhaust and header systems have different oiling system routing and that is a major pain. If you had an earlier car with a 915 transmission you could use the Elephant Universal Crossover Pipe.

The Elephant pipe isn't intended for the G50 transmission but I modified my transmission so it would fit. The Pipe runs across the top of the trans and the G50 has a top rib that interferes. I looked at the rib and how shortened bell housings deal with that area and decided that portion of the rib seems to be under compression instead of tension so I ground it down to clear the pipe.
That has made the swapping of exhaust a breeze.

[Flat Six]

Originally Posted by Quicksilver

NOX levels is partly controlled by the combustion pressure so there is a California specific jumper for that. One of the brown wires from the DME is connected to ground which is the "California emissions option". It causes the timing to be retarded by 4 degrees which reduces combustion pressure. If that wire isn't connected to ground then hook it up. If it is hooked up then disconnect it after smog for more power.
NOTE!!! There is more then one brown wire on the DME. You can do some research on this board to find out which one it is. (#8 comes to mind but I am just guessing from memory so check!!!)

+1 on the brown wire -- connect for emissions testing, disconnect otherwise. Pin 10.

Picture courtesy Steve Wong:





Good luck, hope this helps.

[nkotselas]

Where in SoCal are you? I've got a stock cat hooked up to the stock muffler in my basement

[Flat Six]

Originally Posted by nkotselas

Where in SoCal are you? I've got a stock cat hooked up to the stock muffler in my basement

I'm always (pleasantly) amazed at how helpful and giving Pelicans are -- great offer.

Not sure would work w/B&B headers though; needs stock HEs too, yes?

[blak88]

Flat Six - I will definitely look into the brown wire as I don't recall seeing it when I swapped chips.

Maybe wire had something to do with the last test as it failed both 15 and 25mph nox?

The first time before I touched anything it barely passed 15 and failed 25 but smog check place was down the next block and maybe it wasn't hot enough.

nkotselas - thanks for the offer. I'm in LA/Long Beach area. I know it's far but the PO did give me the stock headers and exhaust (just not sure if they still function correctly)

[blak88]

Here are some pics.



I thought it might be this part but can't find any pics of it.
911/Carrera 3" Catalytic Converter Tip*

[blak88]

Ok. I took a look at the brown wire. It was disconnected. How much would this effect the smog readouts?

If this significantly effects readout then possibly bite the cost to pre-test and smog. Otherwise I'll have to drive an hour to have PO get it smogged. Of course now with the brown wire connected.

[Quicksilver]

The brown wire is mostly Nox. Hydrocarbons need a good working converter.

[blak88]

Good to hear as my NOX levels were the only levels that were high.

905/15mph max565
888/25mph max522