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dang smog; 1993 4 door automatic
Topic Started: Aug 31 2017, 09:10 PM (1,025 Views)
Dystopiate666
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Tree Banger

Higher octane is less volatile, meant for high compression engines that need the fuel to hang on a little longer before igniting (and definitely not pre-igniting). Same thing is going to happen in your metro.
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Woodie
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Moringa
Sep 13 2017, 10:23 PM
Woodie
Sep 13 2017, 06:17 AM
High octane is going to make your emissions worse.
I have no idea how that would work. This statement sounds like a very old wive's tale. If you'd care to elaborate, I'm all ears.
The old wives' tale here is thinking that there is anything premium about "premium" fuel. High octane fuel has crap added to it that makes it slower burning, harder to light off, and it carries less BTU's per gallon (although this is a minuscule difference). Because it is harder to light, you can run more compression and/or more timing advance and thereby get more power. The compression and timing advance are the majik elixir which provides more power, the fuel itself is actually not as good. Because it burns slower, it's more likely to go out the exhaust valve without burning completely (unburned hydrocarbons is what the emissions test is looking for here). Our cars already have a slight problem here due to the late timing of 5°, the sooty tailpipe and burned exhaust valves of the vast majority are testament to this fact. It's the same phenominon which causes oil burneres to burn valves, oil burns hotter and slower than gasoline, so when the exhaust valve opens the charge rushing through it is still burning, eroding the outer edge of the valve.

The only thing that is better about "Premium" gas is that they usually put more detergents in it, and in some locations it doesn't have alcohol in it.
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Moringa
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Living BOT

The slower burning, or less likely to pre-detonate is totally understandable. On a vehicle with a compression ratio of around 10.2 to 1 or less, I could see that there may be less power using premium. I do think that assuming the combustion would be incomplete, if it's slower, may be a stretch. I know that a "later burn" would heat up the exhaust system more, particularly the manifold. One thing that should be a major consideration is the carbon buildups, which these 1.0L engines get. The rings are pretty thin, compared to other engines. Because of the extra carbon, these compression tests produce results far in excess of what would be predicted, given the 9.5 to 1 compression ratio. So in the end, premium may work better, where the compression ratio is higher than it should be. I do believe in my Metro, there is not a significant carbon buildup. My EGR system works great, and all I use is regular, with no problem, and the timing is 10* advance, instead of 5*. Thanks for pointing the abnormalities of premium out.
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Dystopiate666
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Tree Banger

Its not a stretch.....later explosion=less time to burn...the volatility difference is the main difference between the fuels.....would you expect to see higher emissions from retarding your spark timing? you have essentially done close to that by introducing a fuel that won't spark off for a few more degrees.
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Moringa
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Living BOT

Retarding the timing reduces emissions, particularly NOX. Trust me, there's nobody on this forum that understands emissions, as they relate to the operating system, and controls, better than me.
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ice
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alex smiles

So I am a little confused. I and the wife have had this debates about high octane vs. regular 87 octane.
I always put in the high octane premium always. If she drives it and it needs gas she always puts in the cheaps 87 octane.
Then we argue and I bann her from driving it...

Who is right here?? Do i have to buy her a premium ice cream?????
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Metromightymouse
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Powdercoat Wizard

Your engine is set up to run regular. As long as you are using premium brand gas, there is no advantage to you running premium octane gas, unless there is something wrong and your engine is pinging.
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evmetro


Metros like the cheap stuff best.
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1DCGUY
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Don't be a "Richard"

ice
Sep 14 2017, 05:50 PM
So I am a little confused. I and the wife have had this debates about high octane vs. regular 87 octane.
I always put in the high octane premium always. If she drives it and it needs gas she always puts in the cheaps 87 octane.
Then we argue and I bann her from driving it...

Who is right here?? Do i have to buy her a premium ice cream?????
Sorry, but your wife is right.

I know this is hard to accept, and we've all been there and had to admit it once or twice in our lives. :whistle

Buy her the ice cream!! :thumb :thumb
Edited by 1DCGUY, Sep 15 2017, 07:22 AM.
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ice
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alex smiles

dang! is it too late not to ask the question? a do over??
I will never hear the end of it!!!

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MR1 Kingsbury
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Exp. builder/rebuilder

The difference now between reg 87 and prem 91 is like $.60-.75. Huge. I never believed premium was needed in any stock built auto, but I suppose there are some... 25% more in fuel cost is not worth it ever....
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Woodie
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Good point MR1 Kingsbury. Need to be careful when shopping cars by gas mileage, many like the Smart car and MINI require high test gas so whatever mileage they're bragging about should be reduced 25% to compensate for the crazy expensive gas.
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