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  1. #1
    Senior Member Michigander's Avatar
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    Octane levels and temp.

    I've been told that lower octane levels burn more cleanly at a certain cold temperature. I need to know first of all if this is true, and second if it is, what temp is it where you want to switch to 87?

    I disabled my EGR valve, so this is important.
    Bring back the Sig Test!


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  2. #2
    Hey guyz? Guyz? Wait up!! Siu Blue Wind's Avatar
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    Get rid of that FORD and get a Chevy. Heeey. Ford, Furd.............heh.
    Quote Originally Posted by Buddha
    We are what we think. All that we are arises with our thoughts. With our thoughts, we make the world.
    Quote Originally Posted by making View Post
    Please dont outsmart the censor. That is a very expensive censor and every time one of you guys outsmart it it makes someone at the home office feel bad. We dont wanna do that. So dont cleverly disguise bad words.

  3. #3
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    Fords always screw me over.

  4. #4
    Senior Member Michigander's Avatar
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    Quote Originally Posted by Pheard
    Fords always screw me over.
    Thats because you have a ford car. Mine may as well be a truck the way its built. And ford trucks are built to last.
    Bring back the Sig Test!


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    Ok. So mich. You're deep in the heart of the funzone, and siu is going to the funzone. What the heck is the funzone then.

    Is it like the discovery zone? if it is, I want in.

  6. #6
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    Quote Originally Posted by Pheard
    Ok. So mich. You're deep in the heart of the funzone, and siu is going to the funzone. What the heck is the funzone then.

    Is it like the discovery zone? if it is, I want in.
    More like Chuck E. Sleaze.

  7. #7
    Senior Member Michigander's Avatar
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    Quote Originally Posted by Pheard
    Ok. So mich. You're deep in the heart of the funzone, and siu is going to the funzone. What the heck is the funzone then.

    Is it like the discovery zone? if it is, I want in.
    DZ is for small kids. Us grownups have fun, like in the funzone.
    Bring back the Sig Test!


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  8. #8
    Senior Member
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    Don't know about a "funzone," but I know "I can't stop messing with danger zone...." *thinkin' she-bop*

  9. #9
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    Quote Originally Posted by Michigander
    DZ is for small kids. Us grownups have fun, like in the funzone.
    For some reason when I think back to when I was like 10, I get the most awesome warm feelings when I think about DZ. That place was so much fun.

  10. #10
    Senior Citizen lyeinyoureye's Avatar
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    Lowers temps allow more heat to flow from the radiator, and consequently, from the engine block. How much? Who knows, it depends on the specifics. I wouldn't suggest dropping below the manufacturer's rating unless not going to flog the engine for that tank. And reconnect your EGR valve, it may increase the intake charge temps, but it also reduced pumping losses at low load, which increases mileage. Not to mention the emissions side. Disabling the EGR valve in order switch to 87 octane gas for financial reasons is... eh, kinda pointless. Not that you're doing this, but if you are, don't. And a few cents is not worth risking high load detonation, and your engine...

  11. #11
    The quieter you become... Falkon's Avatar
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    That, and many ECUs will run the vehicle very rich if you disconnect the EGR.
    Quote Originally Posted by TechKnowGN
    San Jose has to be the most boring place I've ever been. And I live in Ohio.

  12. #12
    Hey guyz? Guyz? Wait up!! Siu Blue Wind's Avatar
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    Quote Originally Posted by Falkon
    That, and many ECUs will run the vehicle very rich if you disconnect the EGR.

    I told him that. Thank you for the back up.
    Quote Originally Posted by Buddha
    We are what we think. All that we are arises with our thoughts. With our thoughts, we make the world.
    Quote Originally Posted by making View Post
    Please dont outsmart the censor. That is a very expensive censor and every time one of you guys outsmart it it makes someone at the home office feel bad. We dont wanna do that. So dont cleverly disguise bad words.

  13. #13
    Senior Member Mr. Gear Jammer's Avatar
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    Quote Originally Posted by Siu Blue Wind
    Get rid of that FORD and get a Chevy. Heeey. Ford, Furd.............heh.
    Chevy , i have a cavalier. Runs very well indeed.
    Tropical pole vaulting is the shiznit.

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    Quote Originally Posted by Mr. Gear Jammer
    Chevy , i have a cavalier. Runs very well indeed.
    I have a chevy cavalier too. The spark plug wires like falling off while I'm driving.

    I installed them myself.

  15. #15
    later free_pizza's Avatar
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    Quote Originally Posted by Pheard
    The spark plug wires like falling off while I'm driving.
    Did you ins...
    Quote Originally Posted by Pheard
    I installed them myself.
    nevermind

  16. #16
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    Quote Originally Posted by free_pizza
    Did you ins...

    nevermind
    Hey. I installed the push button starter too.

    I got skills.

  17. #17
    Senior Member DannoXYZ's Avatar
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    Quote Originally Posted by Michigander
    I've been told that lower octane levels burn more cleanly at a certain cold temperature. I need to know first of all if this is true, and second if it is, what temp is it where you want to switch to 87?

    I disabled my EGR valve, so this is important.
    EGR lowers the combustion-temperatures in the chamber by diluting the air-fuel mixture with exhaust. This serves to lower NOx emissions. If you disconnect it, you may gain a little power from hotter-combustion. I have no EGR or air-pump in my car at all and tune for emissions with the laptop.

    As for octane, ther's A LOT of misunderstandings and misconceptions on what "octane" refers to. Please review the Gasoline FAQ for background info. I also wrote up a summary of what octane is and isn't here: CornerCarvers - Mixing Race Gas and 91 Octane, What do you get? (post#18 halfway down page).

    As for lower-octane burns "cleanly at cold temps", it's actually a side-effect of the change in gasoline blend during the winter months. Typically, 92-octane is the highest you get at the pump. In the winter, alcohols and other oxygenates like MTBE are added to provide extra oxygen in the fuel. Up to 10% is usually added. This has the effect of lowering gas-mileage because you have fewer hydrocarbon atoms per gallon (oxygen molecules are damn BIG!). It also has the effect of increasing evaporative volatility (Reid Vapour Pressure) of the gasoline, something you actually don't want in the hot summer months. And it lowers octane of the gasoline to 91-octane.

    So yes, the 91-octane gas with alcohol/MTBE DOES burn cleaner in the winter (as in lower HC emissions during the warm-up). But that's not because of the lower octane, it's because of the additives. It's also possible to add other additives along with the alcohol like toluene/xylene and actually raise the octane to 93 and still have a cleaner burning fuel than the summer blend.

    As for 87 vs. 91 octane, there's no difference as far as the additives package. It's changed at the refinery depending upon the weather. Only two concoctions are delivered to the gas-stations, 87 & 91. These are blended 50/50 to give the 89-octane blend in the middle. They ALL burn equally "clean" in terms of emissions.
    Last edited by DannoXYZ; 01-16-07 at 05:20 PM.

  18. #18
    Senior Citizen lyeinyoureye's Avatar
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    I should also add that EGR increases intake charge temperature, but limits peak combustion temperatures. Just so those two don't get confused.

  19. #19
    Senior Member russiankdi's Avatar
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    When the engine is running cold, your exhaust combustion won't be that clean. I have a carburetored car, and in the morning the fumes smell like burned gas. After it's warmed up, it smells clean or at least not bad. Anyways back on subject, octane level will not have anything to do with how clean it burns. Higher octane just burns at higher temps then lower octane gas. So with higher octane, the engine creates more compression, that's pretty much it.



    P.S. Octane mostly has an effect on how the engine is running, not how clean it burns the fuel. A well tuned engine will burn gas properly and will be clean.
    1978 Schwinn Varsity Single Speed

  20. #20
    Hey guyz? Guyz? Wait up!! Siu Blue Wind's Avatar
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    Burned gas? Uh oh. Mine smells like condensation. During high idle warm up it seems like your air/fuel mixture might be off. Unless mine is not rich enough.....
    Last edited by Siu Blue Wind; 01-16-07 at 06:21 PM.
    Quote Originally Posted by Buddha
    We are what we think. All that we are arises with our thoughts. With our thoughts, we make the world.
    Quote Originally Posted by making View Post
    Please dont outsmart the censor. That is a very expensive censor and every time one of you guys outsmart it it makes someone at the home office feel bad. We dont wanna do that. So dont cleverly disguise bad words.

  21. #21
    The Site Administrator: Currently at home recovering from a couple of strokes,please contact my assistnt admins for forum issues Tom Stormcrowe's Avatar
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    Quote Originally Posted by russiankdi
    When the engine is running cold, your exhaust combustion won't be that clean. I have a carburetored car, and in the morning the fumes smell like burned gas. After it's warmed up, it smells clean or at least not bad. Anyways back on subject, octane level will not have anything to do with how clean it burns. Higher octane just burns at higher temps then lower octane gas. So with higher octane, the engine creates more compression, that's pretty much it.
    Higher octane actually = lower flash point with hotter and more even flame front from the detonation in the cylinder as well as a greater release of energy from the same volume/mass of fuel air mix.

    Kind of like the difference between ammonium nitrate/diesel fuel vs propane/O2(Pure) mix
    on light duty due to illness; please contact my assistants for forum issues. They are Siu Blue Wind, or CbadRider or the other 3 star folk. I am currently at home recovering from a couple of strokes. I am making good progress, happily.


    . “He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you.”- Fredrick Nietzsche

    "We can judge the heart of a man by his treatment of animals." - Immanuel Kant

  22. #22
    Senior Member russiankdi's Avatar
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    Quote Originally Posted by Siu Blue Wind
    Burned gas? Uh oh. Mines smells like condensation. During high idle warm up it seems like your air/fuel mixture might be off. Unless mine is not rich enough.....
    Yea...when your car warms up at 2500rpm it smells like that. My car is run completely by vacuum. There is only the slow heater choke that is electronic, otherwise it's all vacuum. Honda designed this engine to ruin very rich during warm up. It will only smell like burned gas when its warming up at 2500rpm. After about 5 minutes, tap the gas and the idle will go down to 1500rpm and everything smells fine. Then when the engine has warmed up completely, the idle goes to 950.
    1978 Schwinn Varsity Single Speed

  23. #23
    Senior Member russiankdi's Avatar
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    Quote Originally Posted by Tom Stormcrowe
    Higher octane actually = lower flash point with hotter and more even flame front from the detonation in the cylinder as well as a greater release of energy from the same volume/mass of fuel air mix.

    Kind of like the difference between ammonium nitrate/diesel fuel vs propane/O2(Pure) mix
    c`mon im 16, give me a break.
    1978 Schwinn Varsity Single Speed

  24. #24
    The Site Administrator: Currently at home recovering from a couple of strokes,please contact my assistnt admins for forum issues Tom Stormcrowe's Avatar
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    Quote Originally Posted by russiankdi
    c`mon im 16, give me a break.
    Arm...or leg?
    on light duty due to illness; please contact my assistants for forum issues. They are Siu Blue Wind, or CbadRider or the other 3 star folk. I am currently at home recovering from a couple of strokes. I am making good progress, happily.


    . “He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you.”- Fredrick Nietzsche

    "We can judge the heart of a man by his treatment of animals." - Immanuel Kant

  25. #25
    Senior Member DannoXYZ's Avatar
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    Quote Originally Posted by russiankdi
    Higher octane just burns at higher temps then lower octane gas. So with higher octane, the engine creates more compression, that's pretty much it.
    That's completely NOT TRUE. Back to the Gasoline FAQ for you!

    Here's the pertinent section: Chapter 6) What do Fuel Octane ratings really indicate?. The ONLY thing octane indicates is AKI-anti knock index. There's even disagreements on how to quantify knock. Regardless of that, octane is NOT:

    - combusion temp
    - flash-point (ignition) temp, actually radical akyl-group formation is what causes knock
    - flame-front propagation speed
    - combustion pressure
    - power (87 will yield exact same power as 91 on same engine)
    - emissions
    - smell, taste or any other perverted uses you have for gasoline.

    All the above factors can be custom-tailored in gasoline independent of the octane-rating.

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