Colorado Emissions Testing - to cat or not to cat

[911boost]

Well this year I finally had to get the 911 past emissions, the whole ball of wax, visual sniff test, everything....

The whole process started back in April when I took it in and passed for the visual (the car has B&B headers with heat and not cat) which was a surprise. I failed the emission portion on CO and HC, both were twice the legal limits....

So off to shop the car went and after a bunch of back and forth discussion with Steven at Poudre Sports Car, I decided to do the right thing and have a new muffler and tip made by B&B with the catalytic convertor ($$$ ouch).

Fast forward to the end of July and I am still waiting for the exhaust... There goes pretty much the entire driving season, since my plates had expired in April. After putting some heat on B&B they finally built it and sent it to me. While it is a nice piece, I wish it wouldn't have taken so long....

After installing everything I took the car back in and failed miserably! The CO was ten times worse after the cat install! WTH.... hmmm, back to the drawing board. I figured the car was running pig rich for some odd reason since we had adjusted the mixture once already (11 mpg on a tank of gas confirmed it). After looking at it Steven (who I called and thanked, he busted his butt on this one) decided to replace the O2 sensor.

I think at this point it is important to point out my turbo has been pretty heavily modified, with twin plug ignition, cams, etc. While still utilizing a lot of the stock electronics and relays its always been more difficult to trouble shoot than a completely stock car, I liek the power though .

With the new 02 sensor in, the car had rock steady idle, and seemed to be running much better. So I took it in again and passed with flying colors! Whooo hoooo. I plan on fattening the mixture up a bit here in the next week or so...

My question for those of you that have read the whole post, and I thank you, is do I leave the exhaust on with the catalytic convertor? The car seems to run fine with it, its a little bit quieter, which is ok. I am leaning towards keeping the old exhaust, but leaving the new one on. I figured I might as well protect the enviroment a little....

I am going to replace the wastegate spring with the 1bar one to pick up any of the power I could potentially lose....

So, Cat or no Cat?

And I like the crowd in OT, which is why I posted it here...

Bill

[HHI944]

If it's not hurting power and it keeps you 100% playing by the rules, I'd just leave it how it is. Besides, swapping it out is just one more opportunity to scuff something up.

[Jrboulder]

If you do take it off you will need to decelerate past the air care Colorado vans on the on ramps or I've been told they can make you come in for another test.

[VincentVega]

Make sure the a/f #'s are good, not just that the idle is good. No fun burning a piston or valve. The cat could great more heat in the exhaust, keep an eye on temps and any material close by, especially plastic. If all that's fine, I would leave it in.

[slow&rusty]

Bill - Removing a CAT on a 930/965 gains about 18-20 or so hp and about the same torque.

If you are happy with the cat on and feel good about environment, I say go for it.
Yasin

[911boost]

Yasmin, the cat is in the tip, so the car still has the headers on it etc.

Bill

[911boost]

Vega, we are monitoring the af's and the 02 sensor is doing what it's supposed to and adjusting the mixture on boost and off boost...

[onewhippedpuppy]

Originally Posted by BSiple

Yasmin, the cat is in the tip, so the car still has the headers on it etc.

Bill

It's still a restriction in the system. Though assuming that it is a modern high flow cat, they are pretty darn good and don't sap much power.

[slow&rusty]

Who is "Yasmin"?

[911boost]

Sorry slow my phone autocorrected....

[Nickshu]

Hi Bill

I live in Ft Collins too. My SC with SSI heat exchangers and no cat passes the visual inspection every time at the local testing station. It did fail one time because I had my O2 sensor unplugged and the mixture too rich so now each time I go in I just hook up the O2 sensor and lean out the mix, get it good and hot and it passes just fine. However I have alot more leeway on a CIS injection system then your newer 911 does.

I say ditch the cat. It will most likely pass without it. The guys at the testing station think that the heat exchangers are cats. Even if you don't pass you can just keep the cat and put it back on.

[911boost]

Hey Nick, I passed the test both visual and sniff, my question was geared more towards keeping the cat or, taking it off and putting the od exhaust on......

We will have to grab a beer sometime...

ill

[aigel]

Tell us what cat you have. If it is a high flow modern cat, it will not cost any noticeable amount of power and I would definitely leave it on.

G

[f5niac]

You should be ashamed of yourself. Sell that car to me and be rid of your guilty conscience. (I'm in Ft. Collins also. +1 on Steve at Poudre Sports Cars, he's a very knowledgeable Porsche mechanic. Nice guy, too.

[Nickshu]

Originally Posted by BSiple

Hey Nick, I passed the test both visual and sniff, my question was geared more towards keeping the cat or, taking it off and putting the od exhaust on......

We will have to grab a beer sometime...

ill

Anytime Bill. Just send a PM.