Octane Level's

Discussion in 'Gen 2 Prius Main Forum' started by Prakash, Mar 22, 2006.

  1. c4

    c4 Active Member

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    I don't think it's true... I can certainly see a difference using premium fuel on my Prius.. I think in general that any system that is smart enough to retard ignition is also smart enough to advance it to the optimum point for a given fuel.. You may not derive the full benefits of the fuel, but you should get something..

    On my Classic which currently has over 200,000 km on it, I can use 87, but under more than moderate engine load (ie, anything greater than about 22-25kW output), you can hear the engine clattering, and if you really ask for power, the noise is much worse.. With 93, the engine is quiet unless you really floor it, and even then the clattering is much less pronounced than with 87.. I find I'm also getting much better mileage on the premium fuel, to the tune of 4-5 MPG (ie, its consistent and noticable on the MFD)..

    My initial thought was that it required valve/lifter adjustment as the sound is very similar to what misadjusted lifters sound like on a Honda, but the Toyota doesn't use the same valve system, and octane shouldn't affect valve sounds, so it must be ping or knock.. I'm going to have to look at the ignition angle with the Miniscanner next time and see what's going on at high load- perhaps my knock sensor is bad..
     
  2. yauman

    yauman New Member

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    I think that statement is true for almost any cars on the road today. Higher octane fuel do NOT burn cleaner, higher octane fuel do NOT get you more mpg's. So, if the manufacturer recommend 87 octane, why do you want to spend more money and put in 93 octane? So, if you use higher octane fuel, the engine will experience incomplete combustion, resulting in higher emission and more engine deposit.

    ( I don't know ifyou know this already, but I'll repeat since most people somehow get the concept backwards: - here's the deal - the HIGHER the octane rating is, the MORE DIFFICULT it is to burn the fuel. Octane in fuel is the measure of RESISTANCE or RELUCTANCE to combust. Pinging in an engine is due to premature combustion, that;s why if the engine pings, you have to use HIGHER OCTANE fuel - ie less likely to combust or change the timing. I hope this clarifies things a bit since you seem to have asked the same question so many times in this thread about benefit of using higher octane fuel. Vegetable oil you cook with have an octane rating of over 400! OK?)
     
  3. tripp

    tripp Which it's a 'ybrid, ain't it?

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    All right, my next tank will be 85 Octane. We'll see how it goes. I'll report back with the results.
     
  4. aaf709

    aaf709 Ravenpaw of ThunderClan

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    They had on the History Channel a program on gasoline and mentioned that. The chief components in gasoline is Hectane (which burns VERY quickly) and Octane (which doesn't). 87 Octane means that 87% of the mixture is Octane.
     
  5. MarinJohn

    MarinJohn Senior Member

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    I live pretty much at sea level and use 87 octane always, even when I occassionally go to the Sierra and it seems fine even at 7-8000 feet.. I have used higher octane as an experiment to try and get better mileage, but it doesn't seem to have any effect.
     
  6. Prakash

    Prakash New Member

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    I just called up Toyota at (1-800-331-4331.)


    A Toyota "Hybrid Specialist" said:

    "87 is sufficient"

    "91 will not provide any advantage"

    "87 is the way to go"


    -
     
  7. jeromep

    jeromep Member

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    I'm sure glad that Toyota told you right on that one. Not that we weren't.

    A word about Wikipedia. Nice place. I've contributed there a few times. The biggest problem is that it is a "wild west" kind of place and edits are done to material by individuals in which the facts they present may not be fact at all, or the language they use to explain something is very unclear. Wikipedia is nice, but double check their info, always.
     
  8. Prakash

    Prakash New Member

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    Thank you for the information. And thanks to all who helped me resolve this issue. I got a little fustrated with this one. I promise no more posts on this topic for a while. :p

    Have a nice day all :)

    ps: i pumped 87..
     
  9. flareak

    flareak Fleet Captain

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    i pump 2309482390572389480239lbs

    ahhhh *gloat*
     
  10. richard schumacher

    richard schumacher shortbus driver

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    [erased as superfluous]
     
  11. Gen2

    Gen2 Member

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    You have a problem my friend. If your Prius is knocking on 87 octane you need to get to the mechanic and have the car seriously looked at. Just filling up with high octane fuel is just masking the problem temporarily, not fixing it. Best case, you have some carbon deposits for which they would be happy to take your money and clean them out. Worst case, the deposits and/or something in engine control is going wonky (knock sensor, ECU, who knows) and you could eventually blow a hole through a pistion when you've exceeded the knock limit of the fuel you are using.

    As for an engine being smart enough to advance the timing to take advantage of the owner putting in excessively high octane gas, I'm sorry to tell you that it just doesn't work that way. The factory designs for a specific range of uses and regionally available fuel to deliver the compromise they wish to put in the showroom floor for you. The compromise for the Prius led to a design which is optimised for 87 octane so that is where you will get the most benefit (there are more factors than ignition timing to this equation).

    It is true that there are a few auto manufacturers that design the engine for best performance using 97+ octane fuel, then have an ignition system with enough lattitude to be able to retard the spark so much that it will work with 87 octane. The problem is that those designs are not optimal at 87 octane and thus lose a lot of power running with 92 or 87 (if I remember correctly it was Mercedes that started this trand so they could advertise more horsepower with the same engine).
    Personally, I prefer a design optimised for 87 so I don't have to waste any money. :)
     
  12. Gen2

    Gen2 Member

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    If I may expand on this:

    Most gas today has very little to no Octane in it at all. It has become a far more complex mix. What they do with the Hectane/Octane mix it to put it into a test motor to test for knocking. What happens is that they start with the new blend of gas and try it in the test motor until it begins to knock. They then lock down the settings and rerun the test with the Hectane/Octane mix. They increase the level of Octane until the knocking just goes away. The percentage of Octane in the mix becomes the "Octane rating". Thus 87% Octane becomes 87 Octane rating. This is called the Motor Method.

    A different test that is essentially performed in a research lab will generate an Octane rating number using the "Research Method". Of course one deliver a number that is higher than the other so onsumers would get ripped off when buying under rated gas. In steps the government and we now have the average of the two which you will see on your gas pump as R+M/2. Everyone is now happy and we all live in peace. :)
     
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