FRporscheman

Why didn't you start your own thread??

I haven't heard of using acetone, but I'll assume it does the same thing as denatured alcohol or ethanol. Using those will improve CO and HC numbers but will raise NO (iirc).

What were your numbers from the first smog test?

azbanks

I didn't start my own thread because there are already a ton of threads about failed smog tests. I didn't want to add to the clutter. Acetone is supposed to lower NOx(from what I've read in other smog threads. Here is the retest fail sheet. The first numbers are at the bottom.

kev951

CA smog tech here. .You have no oxygen left over for you cat to react correctly. As long as you are certain you dont have any major exhaust leaks, your cat is toast

azbanks

No exhaust leaks.


So a new cat is the only fix?

Rogue_Ant

You do have some room to trade HC for NOX...
However, the 944S/S2 is very aggressive about its closed-loop operation, so adding fuel via the FQS might not do much for an emissions test.
You could try adding fuel via the FQS, or removing some ignition timing via the FQS... Doing both might eat up all the margin you currently have on HC.

If you would try again, then I would either add fuel or remove timing. Additionally, I bump up rear tire pressure by 10psi or so. The idea being to try and get rolling resistance down.

azbanks

Could I do more than 6 oz of acetone in a full tank of gas?

Rogue_Ant

I wouldn't. Acetone lowers the surface tension of the fuel. This helps with atomization, possibly resulting in a more homogeneous air/fuel mixture. But I wouldn't run any more than what you currently have in there..

azbanks

the acetone and going to fqs position 5 got me an improvement. Should I try fqs position 7?

Rogue_Ant

Yeah, and high tire pressure, and make sure the exhaust is HOT before testing..

william_b_noble

a new cat is not terribly expensive, why damage the car to avoid what you will have to do anyway?

azbanks

Because fairly soon after I get it to pass smog and renew the registration, I'm taking it off the road to swap in the turbo engine from my old 951. It has a new cat so I don't want to buy one for this exhaust when it is just going to get replaced.

kev951

I'm sure you can find a nice cheap factory cat from a fellow rennlister, otherwise, generic cats are dime a dozen. Opt for the three-way cat

doabarrelroll

Drive the hell out of it before pulling up to test.

V2Rocket

Howabout "borrowing" the 951 exhaust for the S2 smog test? Cut it off the turbo pipes and add another flange

azbanks

I don't want to screw up the turbo exhaust just to pass the test. I don't need the current exhaust long term, I need the turbo exhaust long term.