Passed Smog, Why did my #s change?

84porsche · 84porsche's Garage

Guys,

I took my P-car for a smog test today at a test only center to the exact one I took it 2 years ago and I was expecting similiar results yet my numbers dropped significantly. I didn't do anything to the exhaust and no changes to the engine besides oil. Can someone explain to me what might have happened? The NO dropped almost in half.

02/22/2006

03/03/2004

rrpjr · 02-22-2006, 05:32 PM

Congratulations. Good to hear an 84 making it. Mine comes up soon.

DW SD · 02-22-2006, 05:43 PM

The cat could have been more warmed up this time. OR the engine could have been more warmed up. Different atmospheric conditions, could effect a bit, too.

Geo9146GT · Geo9146GT's Garage

There is always some variability in the emissions from any engine. The cat might have been just a little hotter than the last time, or some other variable was behaving better than before. you can run the same car thru an emission test three times in 15 minutes and get three slightly different results. Also, how often do the test cener calibrate their equipment - once a day, once an hour? This test tells you that your car is running perfectly - just look at the CO2 - 14.5% is as good as you can expect from a 22 year old car. Cheers

Joe Bob · Joe Bob's Garage

Car was in tune, valves were adjusted, better/different brand gas....lot's of reasons.

Moses · 02-22-2006, 05:54 PM

My '83 just passed today! It's a clean machine.

Geo9146GT · Geo9146GT's Garage

Wow Moses!
14.7% CO2 - that's almost unbelievable!
And the other #'s are pretty stinkin' good too.
That cat (or cat's) is really smokin'

Moses · 02-22-2006, 06:19 PM

Quote:

Originally posted by Geo9146GT
That cat (or cat's) is really smokin'

I have a pair of RandomTechnology high flow race cats.

450knotOffice · 450knotOffice's Garage

Congrats, Chris. Good numbers.

I hope my '84 passes in July.

pbflyz · 02-22-2006, 09:13 PM

Hi Chris,
I saw your post and went out to the car and dug out my test results from 2004. They're almost identical to yours, though my CO numbers are much higher (reminder to self: keep the garage door open when engine running

When I had mine tested, it had just been tuned and was plenty warmed up. I was pleasantly surprised to have passed the test at all!
-Paul

84porsche · 84porsche's Garage

I am glad she passed. But based on what you guys are telling me, I believe that it is either outside conditions, temperature of engine/cat or recalibrated equipment. The car has not had adjustments to the valves etc. since I bought her. But I have always run premium except I don't run Unocal 76 brand in her anymore (strictly Shell V-Power and or Chevron 91 Octane). Thanks for all your help.

Moses, glad to see you passed as well. Your NO is definitely lower than mine. Is that due to the cat(s) you have?

Scott, good luck on your test in July. I went to Super Smog on Auto Center Drive in Irvine (down the street from Wahoos) and the guy who works there is a nice guy.

Moses · 02-23-2006, 05:40 AM

My numbers are likely due to the fact that the motor is a '98 993 motor. I messed around with innumerable exhaust setups and settled on a Dynomax muffler with two RandomTechnology cats. I did before and after dynos and the cats had no effect on my HP or torque, so they are staying in the car.

vash · vash's Garage

damn, moses! is your smog guy blind?

congrats!!!!

84porsche · 84porsche's Garage

Well - thought I would revive my thread from 2 years ago. She passed again. Although I did have a new O2 sensor this time. The part I couldn't believe is that my registration is $69.00 and the smog today cost me $68.75. $49.75 for the test, $10.00 for some new evap test required since December and $8.75 for the certificate. I am a fan of the environment but geez I thought I was finally getting a break on the registration.

Also, is it true that if you qualify for historic plates in CA that you no longer have to have your vehicle smogged. Any truth to this? I know that she has to be 25 years old to qualify.

ossiblue · 03-08-2008, 03:51 PM

First of all, congrats on passing smog again--it's always a sweat until the numbers come in. As far as the historic plate/no smog question, sorry, but they are not necessarily related. Your car must be a 1975 model year or older to be exempt from smog, no historic classification needed. I believe cars can qualify for historic plates after they are 25 years old and I guess there are some advantages to that, but not smog exemption, unfortunately.