91 octane

Discussion in 'Engine Performance + Maintenance' started by thegawd, Jan 12, 2021.

  1. L31MaxExpress

    L31MaxExpress I'm Awesome

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    Bone stock 5.7 Vortec on the stock tune in my Express van had knock retard on 87. Ran 91 top tier, had better power and mileage. Then later tuned it for the 91. Huge difference in torque between stock timing map with 87 octane and knock retard vs 91 octane with the timing cranked up.
     
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  2. CrustyJunker

    CrustyJunker Tractor

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    Your truck should run just fine on your available 87 octane. We've been forced to have E10 in my area for many years now. I heard all kinds of bad stuff from ethanol vs. the Vortec poppets, but I was fortunate to never have a problem.

    Top Tier gas is actually good stuff. It yields best fuel economy on my 87 octane powered vehicles. One Chicago performance/dyno shop recommended Shell 93 octane exclusively in one boosted build. -I asked why and was basically warned with a wordy "trust me, don't do it."

    Octane tests are pretty strict and must meet or exceed certain values. Those doing the bare minimum get bare minimum results.
     
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  3. BNielsen

    BNielsen I'm Awesome

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    Something that helped me deal with certain gasoline was running a fuel stabilizer/additive.

    Now I know some people are "fUeL aDdItIvEs R sNaKe OiL" and some of them are.
    But I've had great luck with Amsoil Upper Cylinder Lubricant. The truck definitely felt peppier after 2 or 3 tanks were treated and run out, even with my fuel pressure issue I've been battling.
    https://www.amsoil.com/p/upper-cylinder-lubricant-ucl/

    That's just me though. My truck has been 0411 swapped and I believe tuned for 89; it's a 454 so I don't expect 20 miles to the gallon, but I did pick up 5 or 10 more miles per tank on the additive. And the only major reason I even started running the stuff was because I got it heavily discounted with a motor oil order.
     
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  4. Sportbike23

    Sportbike23 OBS Enthusiast

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    I was under the impression that the octane number wasn't necessarily better or worse for the engine when comparing 87/91. What was better about 91, or the "premium" grade, was that it contained additives and detergents not used in the "regular" gas 87 octane.
     
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  5. Rob7233

    Rob7233 Newbie

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    Maybe we got into the weeds here. I think that the original poster realize his boost in power NOT actually by any octane boost but by the fact he used Ethanol Free (pure gas) in his vehicle.
    Some state up to 30% more power per gallon over the corn alcohol version fuel. Just my 2 cents..
     
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  6. thegawd

    thegawd I'm More Awesome!

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    Rob, that is probably 100% true, that and possibly the additives cleaning out any possible dirty deposits. I bought this truck off of a buddy and know everything he did to it. the shorter list is what he didnt do, he didnt touch the fuel system at all or the transmission, but he did a tonne of work to it.

    thanks for your input guys!

    Al
     
  7. thinger2

    thinger2 I'm Awesome

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    All of the above is true, you have just stated it in a different way.
    And a more complex way that arrives at the same conclusion.
    We are saying essentially the same thing but I dont think it helps a newbie to overly complicate things.
    The moral of the story is that high octane will not help and can actually make it worse.
    My statement is a simplification of the process that I put forth to keep someone from wasting his money.
     
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  8. thinger2

    thinger2 I'm Awesome

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    Read it again, slowly
     
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  9. Frank Enstein

    Frank Enstein I'm Awesome

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    With all due respect you are mistaken. The octane rating is a measure of Antiknock i.e. preignition. It does not burn slower due to octane rating. Race gas burns fast because the engines turn lots of rpm. Aviation fuel burns slower even at the same octane. AV gas is designed to not boil/percolate at altitude and piston aircraft engines don't generally turn very high RPM. Octane is only one facet of the fuel. If you tune an engine for best performance with each fuel sometimes you will get a mileage increase. And sometimes that increase pays for the difference in price (not too much nowadays though:D).
    More octane than the engine can use will simply waste your money but with some fine tuning it might help.
     
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  10. F4U-1A

    F4U-1A I'm Awesome

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    I read the F4U-1A Navy Fighter ran on 100AKI (anti knock index). I think that would be $$$ for a GMT 400. Can I start tail gating yet?
     
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