Cat Delete. What do I need to adjust?
 

Hi All,

Car is a 78 911SC. All stock with exception of Danske Muffler. My Cat Converter has a small hole in it. I want to order a "test" pipe and delete the Cat Convertor. No emissions test since tags are classic car.

What would I need to adjust if anything on the CIS if I make the change?

Thank you in advance!!!!!

you do not have to do anything, just enjoy more horsies, about 5 i would imagine;-) and better sound

Ivan

offset your carbon footprint by using less plastics. Forego the straw or the drink lid. Bring your own reusable shopping bags to the grocery store.

But I don't think your CIS is going to care too much.

Perfect, thank you for the feedback. Much appreciated!!!!

Be mindful of the final sound level that you are after. The bypass pipe is just that and can be a little loud if combined with a sport muffler. If so then a premuffler is a better option. Not all are created equally so take a look at the design and materials before you pull the trigger.

Make sure the bypass has an oxygen sensor hole, then you can run a wide band gauge. Best thing you can ever do for a CIS car. I like the AEM X-Series 30-0300 Wide Band, but that's just me.

Yep, check out the M&K pre-muffler instead of just a straight bypass pipe. Better sound, very nice quality materials and construction too.

New member to the 911 air-cooled world, but my first modification to this ‘76 coupe with 3.0 conversion was to drop the old restrictive exhaust and replace it with the Dansk st/st cat delete pipe and matching sport muffler. It has a healthy sound to it - no complaints - and the wifey even approved in her first ride in the car the other evening! Oh, and their matching hardware & gasket kits were excellent fit.

https://i1193.photobucket.com/albums...549681BD3.jpeg

https://i1193.photobucket.com/albums...FD380E043.jpeg

https://i1193.photobucket.com/albums...E2C301950.jpeg

Could'a shed 20 pounds off that with an M&K, just sayin' ...

guys,
I thought he would need to adjust air mixture?

May need to adjust the idle mix a bit richer now that the cat is gone. Who knows what it was set at previously. At least have it checked.

Adjusting idle mix in SOP when deleting the CAT??

I would recommend taking shallower breaths.

I was shocked at the increase in exhaust after I deleted my cat. Since it doesn’t get driven much I can rationalize not putting it back.

Thank you all for your input.

May get some popping and gurgling on hard decel (sudden closing of throttle when previously at high rpms) which many of us actually enjoy.

You'll get more CO/NO/HC wafting into the cabin and more exhaust sound.

Not fun IMO in a targa...

I just got a test pipe for my 81 Targa. We'll see how it all goes this weekend!

M&K a nice, easy 20 lbs savings waaay in the rear...

If you still have the air injection pump and system, delete those while you have the exhaust apart.

I would check the mixture if it's remained the same as before removing the catalyst. Without the old cermaic catalyst the exhausts flow faster and this could cause a leaner mixture. Best is to use a wide band oxygen gauge to monitor the mixture while driving to see if there are any faults.

Thomas

it is the other way around CAT serves a filter for emissions.....that is the reason you always check the mix before cat...and you go for test it is clean after the CAT;-)
Ivan

I mean that the CO mixture should be checked before the catalyst before removing it...of course - after removing the catalyst you can check it at the exhaust exit...
If he's unsure which mixture is adjusted it's alwas a good idea to check it before making any changes. So you can conclude if the engine is in right condition.

Thomas

I loved my Fabspeed bypass, but the fumes were not worth it.

On my 3.2 with the CAT delete the throttle response was amazing and the sound... perfect with the stock muffler... but the fumes at stop lights in LA were not worth it for me and the wife or any other co-pilot...

Now I run the stock Cat and a Fabspeed Supercup and couldn't be happier... still a little less responsive from a stop, but checks all the boxes and I can idle easy without the smell of fumes.

Be safe, Have Fun

you should not have any whatsoever fumes to smell ..really what gasoline are you using and what is the c/o set up?Also what is your cam timing set up ,if you do not have kick from 1000 rpm??

911 3,2 burns very clean....i even passed the smog once with the strait pipe in LA, but back in 2008...

Ivan

Using the sweet 91 octane w 15% ethanol that we get as CA citizens.

All I can say is my 3.2 has a smell that I don't like... so having a Cat is worth the benefit of an absolutely smell free cruise.

My car's fully in tune now, but I'll be running the Cat life personally.

-Ian

try to get toluene at the paint shop that will give the octanes you need.1/2 a gallon per half a tank..that is a sweet sauce..i used it all the time in CA

Ivan

Yup, fabspeed bypass was too smelly for me too. I opted for an active sport-cat and like it a lot. I've a 3.2 with CIS.

I find the comments about smell interesting and certainly contrary to my experience. But then, in my area 93 octane is readily available and gasoline is a maximum of 10% ethanol, unlike the above-referenced 15%.

In my '87 3.2 I am also not running a Fabspeed bypass pipe but am instead running a Fabspeed euro premuffler. Unfortunately, people are not always careful to distinguish these when referencing cat substitutes.

I've run this with the stock-style muffler and with a Dansk 1-in-2-out (84mm). The Dansk 2-out is a bit loud for highway driving so I switch mufflers depending on how I am using the car.

The Fabspeed euro-type premuffler has the bung for the OEM sensor and no re-tuning was needed, but I do have an SW chip (93 octane low-restriction exhaust version) in the ECU.

And because the premuffler gets hot and removal of the cat also meant removal of the heat shields, I wrapped the Fabspeed unit, like I used to do to muscle car headers back in the day.

http://forums.pelicanparts.com/uploa...1699060226.JPG

Smelly exhaust after swapping out a cat for a bypass pipe is often due to the engine being in a less than optimal state of tune. The cat will cover up a rich condition that would normally be looked after if no cat were present.

Replaced my cat with M&K pre muffler and muffler. Great quality and sound. Very pleased.
This on the '88 3.2.