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89 octane?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by coopertwpk, Jun 23, 2000.

  1. coopertwpk

    coopertwpk 1/2 ton status

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    Chevrolet specifically tells you not to run high octane in the TBI trucks and vortech motors ,they say it causes excess fuel consumption and higher smog levels because the fuel will not burn completely,which in turns ruins your cat.
     
  2. DMK

    DMK 1/2 ton status

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    Have an 87 Blazer and it pings on 87 octane. Use 89 all the time. Also used it in my 89 Blazer. Always passed emissions.My 89 got 15mpg in the city. These motors have 9.3-1 compression so 89 should do just fine. Where did you see this at?
     
  3. MudFrog

    MudFrog 1/2 ton status

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    I have an 89 and I've been running 87 but I'd be interested to see how 89 reacts for some of ya'll.

    89 K5 Silverado
     
  4. Brian 89KBlazer

    Brian 89KBlazer 1/2 ton status

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    I've run 87 (reg unleaded), 89 (mid-grade) and 92 (supreme) and found that the gas mileage didn't improve at all. The only reason I stepped up in grades was to try to beat the detonation. Turned out the timing was off by 5 or 6 degrees. Went back to reg and working fine when I parked it.

    Brian
    89KBlazer
     
  5. BigBadBowTie

    BigBadBowTie 1/2 ton status

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    <font color=purple> Octane is dependent on compression. On my 9.25:1 350 I can't run anything less than 92. My new motor 383 will have 9.1:1 compression, hoping I can at least run 89!</font color=purple>
    [​IMG]

    <font color=purple>Rick
    86 K-5</font color=purple>

    http://www.BigBadBowTie.ColoradoK5.com
     
  6. dumbfounded

    dumbfounded 1/2 ton status

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    Here's the scoop. When I was younger in the question everything stage I asked my father the difference in gas and being an engineer wealthy and retired I do believe most anything he says. When an engine is developed they use certain octane fuel in tuning. Usually the minimum in your owners manual 87 or 88 octane. So your timing is adjusted accordingly. Now say you have a turbo car or a vette/high perfomance vehicle. These are designed as high performance in mind not fuel economy or drivability they need the high octane for performance not so much the turbo they need it due to the pressures in the combustion chambers during boost. A low octane fuel in normal terms explodes in the combustion chamber and high octane burns. So lower octane usually predetonates in most cars "spark knock or pinging" and retarding timing fixes this but costs power b/c efficiency goes down. A high octane fuel allows higher compression to maintain a reasonable timing setting rather than retarding to decrease efficiency. Most newer cars can compensate using 87 b/c it automatically retards timing to a certain degree, but if it's really bad due to say really hot outside it won't "over retard" so pinging occurs. Now if you set your timing on an old hot rod with 93 octane (going by trial and error) then switch to 87 and you'd thing there are marbles in the engine. The same is true for all carbed vehicles you can run any octane as long as timing is set but for better efficiency high octane at more advanced settings is better but may not be worth the price for the extra pony's. an extra $4 a tank x fill ups/year= alot more. I only run 93 in my vette with 11:1 compression b/c I have to, my other vehicles 87 unless I feel spunky with 89 or once a month 93 amoco to help clean the sys w/ Fuel inj cleaner.

    Wasn't me.............
     

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