URG8RB8

FluidPlay, PM me, I can be of great assistance to you. I passed last year in San Jose and have the data you will need.

gpr8er

anyone have experience of adding some denatured alcohol to the fuel or possibly 100 octane unleaded race gas?

Crazy Eddie

I added e85 on my last smog test to the 100 I had in the tank...
I don't know if it helped or not ?
I failed the first test, then went a tad richer, and passed the second one
It seems its like a balancing act between the NO and the HC with the lean and the rich...

Droops83

The octane booster and fuel additive methods of passing smog tests are pretty much urban myths.

I work on Porsches and BMWs for a living, and while Santa Barbara is a "basic" smog test area with tests in neutral at idle and 2500 RPM only, we do work on a number of cars that are registered in enhanced areas, and therefore need to pass the 15/25 MPH light load tests.

NOx is a byproduct of high combustion chamber temps, which is usually a result of lean running.

The basic requirement is to get your air/fuel ratio as close to stoichiometric (14.7:1 at sea level) as possible, which I imagine that most of you guys do given the fact that wideband O2 sensors seem to be the norm around here.

Beyond that, NOx control is almost entirely a function of catalytic converter efficiency, and it is the toughest job that a converter has. The original factory 951 cat is fantastic, but of course has a finite lifespan. My own personal car still has its original cat and after 165K+ miles still passes smog with flying colors, even after 7 years and 10K+ miles of heavy track use and exceedingly rich mixtures. I must state, however that my engine and engine management are bone stock.

Again, NOx reduction is almost entirely a function of catalytic converter efficiency if all else is well. The sad reality is that aftermarket catalytic converters are manufactured to a price point and simply do not last as long as the OEM ones do. This is why the original poster's emissions numbers went way up after 2 years; I have seen this time and time again on customer cars when they go the cheap route.

I know that OE Porsche cats are probably not available anymore and I am not insisting that they are absolutely needed, but my main point is most aftermarket cats are junk and need to be replaced every few years.

Sorry to be the bearer of bad news!

Brantley

Yes, would agree that increased octane is a myth. I tried 100 octane by first draining my engine of 91 octane. My numbers got no better.

PEvans

So I'm presently trying to get my stock '89 to pass. So far new O2 sensor, cap and rotor and verified good vacuum, 17" at idle. There was no hope with my old DEC cat, so I put in a used OEM cat with unknown history that I bought a while ago. It was definitely better but I'm not yet sure it will be good enough. In the past with a good O2 sensor the HC and CO numbers have been comfortably under the limits; now they are still passable but higher. I don't know why.

pormgb

When I took my cammed LS6 for smog, I was told that it would be hit or miss with my cam. I added 2 ounces of acetone to half a tank of gas; it passed with flying colors to the surprise of my tuners.

There are quite a few articles about using acetone to help pass smog. As with most online advice, you will to decide for you self if it really works.

PEvans

Passed!

15mph (2396 RPM):
HC was 59 (max allowed was 116)
CO% was .27% (max allowed was .74%)
NOx was 651 (max allowed was 791)

25mph (2367 RPM):
HC was 45 (max allowed was 91)
CO% was .27% (max allowed was .62%)
NOx was 602 (max allowed was 730)

This is basically stock and original, with probably well over 200K. New distributor cap, rotor, spark plugs, and O2 sensor. Fixed one vacuum leak and confirmed 17" at idle. I replaced a spent DEC catalytic converter with a used factory catalytic converter I bought a while ago for this purpose. So it got by, but not by much.

It initially failed everything, not just NOx and CO. The HC had spiked which, from this and prior results seems to be an indicator of a bad O2 sensor. That alone was not enough, but I think the replaced ignition components may have provided just enough help for the used OEM cat.

I don't know why the limits in my results are so different from Tom's in the original post. The tests may have been done in the same shop. Maybe a different model year? The the limits quoted in my test results have not changed for quite a while.

Tom M'Guinn

Congrats! Great results for a used cat too! Hang on to that one. Yes, MY86 cars have higher allowed limits than your car -- not by a ton, but the higher NOx limits are helpful as that one is always the toughest...

PEvans

We took your suggestion on the plugs and that probably helped. Thanks for your other offer.

Two years of dispensation from The Authorities to drive my car!

Tom M'Guinn

My car passed smog today with good numbers all around. I bit the bullet and got another new DEC cat, same part number as in the original post. The good news is they fixed the waste gate tie-in pipe, so it's now a true drop in replacement with no modifications needed (other than needing some extra washers to compensate for comically large bolt holes in the football-shaped waste gate tie-in flange). The original DEC cat probably would have been fine, but I wanted to maximize my odds and nothing works better than a brand new cat. If anyone local wants the old one, let me know. It has a wideband port before the cat, and has very few miles on it...

V2Rocket

Got a price in mind for your old one?

Brantley

Congrats, Tom!

I've used my DEC now to pass smog 5 times or so on 2 different cars. Still working good... Numbers did get a little worse on the latest test but that could be due to other things. I don't run it normally so just keep it in my garage for smog time.

lart951

I just passed my lartmobile # 6 with the help of Julio 200

PEvans

I might be interested in trying it. I don't expect my old OEM cat noted above to get me through.

One thing about buying new DEC cats is they will continue to make them. That's good for all of us.