Chevy 350 octane level? do I need 91?

Discussion in '40- & 55-Series Tech' started by wantatlc, Aug 15, 2005.

  1. wantatlc

    wantatlc

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    is it really necessary to run 91 high octane in a chevy 350 conversion? what harm will it do to use 87?
     
  2. Corbet

    Corbet Speski OffRoad LTD. Supporting Vendor

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    What kind of 350?
     
  3. wantatlc

    wantatlc

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    Chevy 350?
     
  4. camcruiser13

    camcruiser13

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    i run the cheapest i can find, i dont race it or need anything more than the cheap stuff
     
  5. wantatlc

    wantatlc

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    but will it damage the engine in some way to run 87? guy I bought rig from said that Chevy 350 with Edelbrock carb needs 91.

    I think not, but do not know for sure and 91 fuel is over 3.00 a gallon here.
     
  6. camcruiser13

    camcruiser13

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    you should be fine, i have had zero probs for over 5 years now on the cheapo, its like the argument that cheveron gas is better than phillips 66 gas. its all the same to me.
     
  7. Bradley

    Bradley

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    Go with the 87 and listen for any pinging underload, if none then you are golden!
     
  8. Corbet

    Corbet Speski OffRoad LTD. Supporting Vendor

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    TPI, TBI, LT1, carbed?

    From the looks of your last post, carbed. You should be fine with 87 unless many performance upgrades have been done to it. (high compression, large cam, etc...)

    Try 87 if it pings play with the timing. You should not do any damage to it.
     
  9. 1FE pig

    1FE pig

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    Compression is the factor,Over 10 to 1 yes it will need higher octane to be happy when screaming down the road.If it is a pull out motor try both.The cute little 350 in the piggie will run on the 89,but with the 91 it's smoother and snaps right up when i nail it.The big block only gets the good stuff.Big horse power=Great cheap thrills in a cruiser.Cheers 1FE
     
  10. Rice

    Rice

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    If this motor is new to you you'll want to do a compression check anyway. Once you know the compression you'll have an answer to your question. With iron heads anything over about 9.5:1 (depending on tuning) will need higher octane. Bigger cams actually lower compression and let you get away with cheaper gas but not a high torque cam. Like the others have said, after you've properly set the timing run some 87 and listen for pings. If it's pinging you can opt to de-tune the engine some or run higher octane fuel. Once you found the minimum octane that makes it happy stick with it. Anything higher gets you nothing.
     
  11. wantatlc

    wantatlc

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    I have no idea of the compression nor how to find it out to be honest.
     
  12. Rice

    Rice

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    That's really okay. If you one day have someone offer to check it for you like a buddy that turns wrenches then do it so you'll have some idea of the internal health of the engine ("leak down" test is actually better). Never the less, like the others have said, run some 87 and listen carefully for "pinging" when pulling a steep hill or accelerating. If there is no pinging there is no danger of damaging the engine. It's that simple.

    If you wish to learn more about working on your own stuff go down to Autozone and borrow a compression checker, then drop me a note and will walk through "how to". Very easy.

    Rice
     
  13. Isotel

    Isotel

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    85 is all i run.. At $2.50 a Gallon

    TBI 350
     
  14. wantatlc

    wantatlc

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    I will take you up on that! once I get that from them.

    for now, I will drop to 87 and see what happens. I wonder if I will even know what a "ping" sounds like and how long after switching to 87 would I expect to start to hear it. within the first tank full?
     
    Last edited: Aug 15, 2005
  15. joey93turbo

    joey93turbo

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    I've found my 350 swapped FJ40 runs much much better on 91, and I also get better gas mileage for some reason. It's usually only $5 more per fill up for the good stuff.
     
  16. wantatlc

    wantatlc

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    yeah, the price is not a huge savings when you really do the average. if it is about 4$ per tank extra at 4 times a month fill at 12 months, that is about a $200.00 savings per year. not huge, but pays for parts on about 4 others fixes I want to do.
     
  17. Bradley

    Bradley

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    Pinging sounds kinda like marbles in a tin can but not really very loud.
     
  18. Yoda

    Yoda

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    Stock compression 327 has run on 87 octane for 20 years in my cruiser.
     
  19. PUPTLAM

    PUPTLAM

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    When you turn off the engine it it tries to keep running (DEISELING), get better gas.
    If it knocks and pings get better gas.
    Run it on cheap stuff, You will know if its okay. You will also know if its not.
    A good running engine just feels right. High compression is the only reason you would need high octane.
     
  20. chief

    chief

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    Higher octane fuel is sometimes necessary in sbc. Depending on the compression ratio of the engine and the load under which it is operated.

    If the engine is a low compression stocker 87 octane is probably sufficient. If the compression is 9.5 or more higher octane will probably be required. The cam timing and the ignition timing will play a part in the octane requirement of the engine. Run the lower octane and listen to the engine for "pings" this sound is detonation. The fuel is not burning smoothly but is actually exploding in the cylinder. This can cause severe damage to the engine (burned pistons) if it is allowed to continue. Test it under acceleration and pulling under load such as up a long hill. If you experience detonation with 87 octane fuel you will need to use higher octane fuel. The elevation you are running at can also cause a change in octane requirement. The lower the elevation the more need for higher octane.
     
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