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Old 02-04-2009, 10:29 AM   #1
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Default Smog test and octane

I've STFA and seen mixed opinions on this. Is there an advantage to using higher octane gas for a smog test? I have up to 100 octane race fuel available to me at the pump.

Thanks.
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Old 02-04-2009, 12:34 PM   #2
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Default nope... try to limit the amount of ethanol in the gas.... use 91...

be sure to change the oil, get it good and hot on the way to the test.

If you know it's running rich, change the mixture.
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Old 02-04-2009, 01:49 PM   #3
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Default a 10% ethanol blend can reduce ALL tailpipe emissions a similar percentage...


Ethanol is one of the best fuel additives we have to fight air pollution from vehicles. Ethanol contains 35% oxygen. Adding oxygen to fuel results in more complete fuel combustion, thus reducing harmful tailpipe emissions. Ethanol also displaces the use of toxic gasoline components such as benzene, a carcinogen. Ethanol is non-toxic, water soluble and quickly biodegradable.

I had to run the "enhanced" test this year, an even more strict test with dramatically reduced "maximum limits" allowed on the dyno and comletely blew away my results from 2 years ago on the same test. And I mean by H-U-G-E margins of between 37-66% cleaner on EVERYTHING across-the-board! And the most recent test with stand alone ECU, high-lift/long duration cams and about 55 more HP than in 2006! 2006 no ethanol/2008 with ethanol.

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Old 02-04-2009, 02:01 PM   #4
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Default I've heard of people having issues with using ethanol-blend fuel...

basically... the older fuel injection systems don't mix well with ethanol based fuels... and emissions go up.

While I've never had performance issues when running ethanol-blend fuels, I have seen (and witnessed with other cars) my cars fail for having Sunoco 94 with 10% (or is it 15%) ethanol content.
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Old 02-04-2009, 02:03 PM   #5
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Default Re: a 10% ethanol blend can reduce ALL tailpipe emissions a similar percentage...

I'm not sure if this is the same where you are, but like Doug mentioned, the fuel in Ontario (or maybe even all of Canada, not sure) has something like 10-15% Ethanol in it now, it's the law. So if Ethanol really helps, then bonus for us
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Old 02-04-2009, 02:05 PM   #6
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Default I don't know either but the proof is in black & white on my "actual" emission print-outs

And yes, we have the same laws requiring oxygenated fuels (ethanol) where I'm at. It used to only be winter months Nov-thru March (i believe) but I don't know if that's become full-time now. Could be as I'm not all that attentive to those little decals on the gas pumps any more ;-)
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Old 02-04-2009, 02:08 PM   #7
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Default but have you tried an 87/89 octane with ethanol? My car runs MUCH cleaner....

emissions-wise on lower octane but MUCH better and only slightly dirtier emissions-wise on higher octane. Something to consider. I no longer switch to lower octane fuel for emissions testing as I now know I can pass using premium or regular.

Ethanol is also a solvent that will dissolve gums and varnishes that gasoline leaves behind. I know there were LOTS of issues early on. But small amounts tend to dissolve those more slowly and over time. May be that some of those cars now have cleaner fuel systems and can more easily accept ethanol in small doses than in years past when this all started.

I don't like having blends put in my fuel but long as I can't feel a performance loss I'll tolerate it. And cleaner emissions with a cleaner planet is ok with me too. But leave my torque alone! ;-)
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Old 02-05-2009, 06:03 AM   #8
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Default Interesting. My results are significantly better this year too.

But there far too many other variables to say what the cause is:

Lower octane fuel (87 v 93)
Warmer outside temps (40 v 25)
Idle (950 v 850)
New 02 sensor
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Old 02-05-2009, 06:58 AM   #9
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Default I didn't mean to imply ethanol being responsible for my 37-66% improvement...

but I will give it the nod for 10-15% of the improvement this year over 2006. Everything I've read indicates if all other things are equal the ethanol blend percentage "going in" is par equal to the emissions reduction amount samplings taken "coming out" the tailpipe, ie; 10% blend is 10% cleaner/15% blend is 15% cleaner etc. That is to say "if" the same car is tested with an oxygenated fuel and then with a non-oxygenated fuel of the same octane rating the tailpipe emissions of the oxygenated fuel tailpipe sampling will be a similar/identical percentage cleaner based on amount of ethanol used emissions-wise than the same car using 100% gasoline of the same octane rating.

Least that's what California/Colorado Air Resources Boards claim. But even if it's not 100% accurate I do believe its VERY close to accurate... maybe within a percentage point or less of empirical.
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Old 02-05-2009, 10:36 AM   #10
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Default Higher octane can also mean more unburnt HC out the tailpipe.

One of the downsides to having a fuel that's less susceptible to explosion is that it burns a bit slower. It's all about chemistry.

So, 100 octane, if you have a 12:1 motor, might burn just fine, and give great emissions results. But at 9.5:1, you might get super-high HC and CO. The relationship between octane number and fuel make-up is really very complicated, and it's super-hard to explain in a web forum.

A lifetime ago, I worked as a petroleum chemist. Things have changed A LOT since then, but the basic chemistry has not. For reference, when I blended gasolines for octane, I used tetraethyllead to increase octane number in finished product. Yeah, that long ago.
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Old 02-05-2009, 10:36 AM
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