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85 Octane fuel in CO.

Discussion in '2nd Gen. Tacomas (2005-2015)' started by Quad D, Jun 16, 2011.

  1. Jun 17, 2011 at 2:28 PM
    #21
    MountainEarth

    MountainEarth Well-Known Member

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    No worries brother. That wasn't aimed specifically at you. Others were saying the same thing. And honestly I wouldn't expect those who live at lower altitudes to know. I grew up at sea level, and when I first moved to Colorado 16 years ago, it threw me too. I just want the guy to know that it absolutely won't violate his warranty or hurt his engine or injectors, or anything like that.

    :canada:
     
  2. Jun 17, 2011 at 2:31 PM
    #22
    Dark Knight

    Dark Knight Well-Known Member

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    A few bolts are different.
    Premium always for my truck.
     
  3. Jun 17, 2011 at 2:39 PM
    #23
    MountainEarth

    MountainEarth Well-Known Member

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    That's because you're one of them rich Breckenridge types.
     
  4. Jun 17, 2011 at 2:56 PM
    #24
    Dark Knight

    Dark Knight Well-Known Member

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    A few bolts are different.
    WRONG. I'm a poor workhorse for all these rich assholes.
     
  5. Jun 17, 2011 at 4:21 PM
    #25
    Quad D

    Quad D [OP] Well-Known Member

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    Colorado, from CA, lived in TX, ID, and MT also.
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    It's great to hear the confirmations. I recently went through a lot of checking for my harley as far as temperatures/octane/comp etc.. and when it came time to fill up the truck I wanted to be sure. I haven't noticed any difference since I've been running the 85. When I moved to CO I was shocked and a little pissed at the lower octane levels all around. I was of the thought that higher octane = more power. When I found out later it was the same "bang" just a matter of at which point it ignites I felt pretty stupid. I'm new to my Tacoma and don't know the compression they run or any of that, (not that I imagine it's very high comp.), so the quick way to find out is ask. "Squeeky wheel gets the grease" and all that.

    Thanks to everyone.
     
  6. Jun 17, 2011 at 4:31 PM
    #26
    OZ-T

    OZ-T You are going backwards

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  7. Jun 18, 2011 at 5:01 AM
    #27
    buddywh1

    buddywh1 Well-Known Member

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    More precisely: how fast it burns. Higher octane fuels burn slower than a lower octane fuels. The burn speed that's optimal for an engine depends on engine design and tuning. Using too low of an octane can result in pinging or knocking under load.

    But since maximum power and efficiency from a given engine design is obtained with fast, complete combustion in the power stroke, it's always best to use the lowest octane fuel it can handle. But that's kinda hard to know because modern anti-knock sensors mask the effect of too-low octane (pinging) by retarding ignition timing. So I think that it's best to just stay with manual recommendations 'cause the engineers know something I don't.

    Engines designed for higher octane have higher compression ratios: think diesel where fuel ignites and burns by compression alone. That happens to too low octane fuel-- the cause of the pinging. The thing about high altitude is that a given intake stroke has less "air" in each gulp since it's so rarefied (the ECU also squirts less gas to keep it stochiometric). That effectively reduces compression ratio so a given engine 'needs' a lower octane fuel. Gas companies know that, so they sell gas that's lower octane at high altitude.

    I regularly drove between El Paso (4000 ft) and Oklahoma (600 feet) where I noticed a very nice improvement in performance because of the richer air. I also remember the (sarcasm on) 'good old days' (sarcasm off) with carburetors: a low altitude car would belch black smoke 'cause the mixture was way too rich until they changed jets for high altitude operation. You probably never noticed that because a dealer at high altitude generally did it for you at or before sale.
     
  8. Jun 18, 2011 at 6:03 AM
    #28
    Quad D

    Quad D [OP] Well-Known Member

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    I agree with everything except this part of your post. I am pretty sure that no matter how much fuel or air is stuffed in a cylinder the compression doesn't change. Compression is set by when the valves close/open, your stroke and size of bore, and the size of the combustion chamber(cc of your heads and dome/concave of the pistons). Too much fuel simply won't burn off. And ambient temperature is also an issue when getting to higher compression ratios. Just cause a given vehicle can get away with 89 oct during winter while cruising doesn't mean it'll be happy on a 110 degree day sitting in traffic with that same 89 octane fuel. Pre-detonation or "pinging" would become an issue. I'm no pro with this stuff though, that's why I talk with guys like yourself about it. ;) I know there is a difference between static compression or corrected compression and actual CCP (cold cranking pressure, which changes with altitude). Either way, I don't think these tacomas are running very high compression as they wouldn't last so long if they did. IMHO. I would like to see some actual numbers eventually, so I've got it on my list of to do's.
     
  9. Jun 18, 2011 at 6:36 AM
    #29
    buddywh1

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    Agreed! that's why I said 'effectively' lowers compression ratio... not actually.

    The engine would still last long: the knock detectors would cause the ECU to retard timing to make the destructive pinging go away. But it would degrade performance in the process.

    From what's published the V6 has a 10.5:1 compression ratio. That should be enough to benefit a lot from mid-grade or premium but apparently Toyota has 'detuned' the engine with a fixed timing map that's way retarded at low throttle pr RPM settings. You have to REALLY put your foot in it to see the timing start to pull because of pre-ignition. So you can get benefit from using premium when towing and you put your foot in it for hill climbs.

    This wasn't something I found out, though. Another TW member posted it: he discovered it by monitoring his scangage when towing and in regular use. Otherwise, and IMHO, save the money and use regular!

    I'm no pro; when I got my Maxima (which does need premium for optiomum performance) this topic piqued my curiosity and went searching for knowledge. Found something called the "Gasoline FAQ" that pretty much revealed all! One just has to apply the principles to figure out what's going on.
     
  10. Jun 19, 2011 at 7:48 AM
    #30
    Goober

    Goober Earthlings are fun to watch!

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    The compression ratio doesn't change at high altitude but since air pressure at high altitude is less the pressure in the engine is less. Effectively less "compression". I worked for a heavy equipment manufacturer in the '70's and our high altitude engines were turbocharged.
     
  11. Jun 19, 2011 at 2:12 PM
    #31
    joes06tacoma

    joes06tacoma Well-Known Member

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    As long as you're going to stay at the altitude that they are selling the 85 at, I don't see any issues. If you were going to have problems, it would be as you drove down towards sea level. The lower in elevation you go, the more prone to knocking that engine would be.

    In reality, the truck is probably able to adjust enough to avoid damaging the engine, but I wouldn't risk it if you know you're going down to lower elevations with it.

    I have an uncle in the Denver area who has several hot rod type cars and trucks. When he comes down to sea level with any of them, he has to stop and retune them to stop from knocking the engines to death. But none of his cars have knock sensors on them either.
     

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