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Smog Index....how Does It Work?

  #1  
Old 11-04-2007, 01:08 AM
Noz
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Default Smog Index....how Does It Work?

I ask this question because everytime I go and see a car at a dealership, they have a smog index that is posted near the window sticker. And everytime, cars seem to have wildly differing indexes.

Case in point:

SMOG INDEX FOR 2007 cars: 0.38 for new vehicles

2008 Nissan Sentra SE-R
177HP, 2.5 L engine.
SMOG INDEX = 0.49

2008 Nissa Altima 2.5
170 HP engine (same engine, detuned, heavier car)
SMOG INDEX = 0.21

2008 Nissan Altima 3.5
270 HP V6 engine
SMOG INDEX: 0.39

Why such discrepent readings?
 

Last edited by Noz; 11-06-2007 at 09:04 AM.
  #2  
Old 11-05-2007, 10:25 AM
Noz
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Default Re: Smog Index....how Does It Work?

Wow....a hybrid car website and not one single reply....very impressive...NOT.
 
  #3  
Old 11-05-2007, 02:18 PM
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Default Re: Smog Index....how Does It Work?

Where do you live? First thought- maybe it's a California thing. I live in Illinois and I'm not familiar with it.
 
  #4  
Old 11-05-2007, 02:58 PM
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Default Re: Smog Index....how Does It Work?

You must be under the impression that hybrid owners are all into emissions and smog ratings. But as I looked over the list of three cars, not one of them was a hybrid. So I kinda wonder, why should I, a hybrid owner, care?

Furthermore, I live in Alabama and we don't even have annual inspections, much less emissions testing. So I'm looking at the original posting and was wondering why you didn't find a Nissan forum to ask these questions?

A Nissan forum would have folks with some mechanical understanding of the different models and might be able to offer a clue. But no hybrid . . . asking about a secondary effect not related to any of our cars?

Now if you'll pose a question about a hybrid, our interest will perk up.

Bob Wilson
 
  #5  
Old 11-05-2007, 08:45 PM
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Default Re: Smog Index....how Does It Work?

The Smog Index sticker only appears on California cars and a few other states that have recently adopted it. A quick google search will reveal that this index is strictly a measure of hydrocarbons, with no other pollutants factored in. The index is not a direct measurement. It is a rating of a cars position relative to a standard for it's class. That's why the Altima scores better than a Sentra with the same engines. The Altima is compared to other cars in it's size class that generally have larger engines.
 
  #6  
Old 11-06-2007, 08:58 AM
Noz
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Default Re: Smog Index....how Does It Work?

Originally Posted by bwilson4web View Post
You must be under the impression that hybrid owners are all into emissions and smog ratings. But as I looked over the list of three cars, not one of them was a hybrid. So I kinda wonder, why should I, a hybrid owner, care?

Furthermore, I live in Alabama and we don't even have annual inspections, much less emissions testing. So I'm looking at the original posting and was wondering why you didn't find a Nissan forum to ask these questions?
I did....no one knows why over there.

A Nissan forum would have folks with some mechanical understanding of the different models and might be able to offer a clue. But no hybrid . . . asking about a secondary effect not related to any of our cars?

Now if you'll pose a question about a hybrid, our interest will perk up.

Bob Wilson
I'm talking about emissions....a subject that affects your cars as much as anyone elses. It should be even a higher priority for you guys. I used the Nissan cars ONLY as an example of differences in SMOG INDEX values....it could have been Daewoos for all I care...the actual cars are irrelevant. But the Nissans were a good example.
 
  #7  
Old 11-06-2007, 09:00 AM
Noz
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Default Re: Smog Index....how Does It Work?

Originally Posted by KenG View Post
The Smog Index sticker only appears on California cars and a few other states that have recently adopted it. A quick google search will reveal that this index is strictly a measure of hydrocarbons, with no other pollutants factored in. The index is not a direct measurement. It is a rating of a cars position relative to a standard for it's class. That's why the Altima scores better than a Sentra with the same engines. The Altima is compared to other cars in it's size class that generally have larger engines.
Hi Ken,

I'm not sure if I agree with that however. I'll tell you why and perhaps you can correct me. The SMOG INDEX sticker has a value printed on it for ALL CARS for that year of 0.38...irrelevant of class. Which also means the values are nominalized for the average shown. Which makes things confusing. Or at least contradictory. This means, given a standardized value, that the Altima engine is FAR more clean burning than the Sentra engine. I still don't believe it UNLESS it's emissions system is somehow just that much better?
 

Last edited by Noz; 11-06-2007 at 09:03 AM.
  #8  
Old 11-06-2007, 07:44 PM
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Default Re: Smog Index....how Does It Work?

You may be right. I did a little more looking and found sources that said the index was compared to cars in it's class and other sources that said compared to all cars of that year. If it's all cars, I can't think of any explanation. As far as I know the engines are identical. Gearing differences should make the Altima worse.
 
  #9  
Old 11-06-2007, 10:35 PM
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Default Re: Smog Index....how Does It Work?

What we've learned about the Prius is hydrocarbon emissions come from:
  1. fuel tank - the Prius uses a bladder tank and sophisticated vapor capture
  2. warm-up operation - the NHW11 uses a special HC capture, exhaust capture system and the NHW20 uses a warming thermos
  3. catalytic converters - not all are made and configured the same
  4. electric operation - the NHW11 and NHW20 use MG2 to handle as much warm-up driving as possible. In fact, there is no 'reverse' but just MG2 and the ICE shuts off when backing out of a driveway.
Your non-hybrid vehicles may have improvements in the first three of these areas and reduce their hydrocarbon emissions. But these first three are subtle changes, independent of the engine block, and would really require a close inspection of the manuals or engine compartments to identify.

You might try writing a letter to the manufacturer with your question.

Bob Wilson
 

Last edited by bwilson4web; 11-06-2007 at 10:37 PM.
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