How to determine octane requirement?
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How to determine octane requirement?

  1. #1
    Senior Member Rivernut's Avatar
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    Default How to determine octane requirement?

    I was told to run 93 octane in my SBC Vortec 5.7. It has about 32 degrees of total timing, stock heads and pistons. Premium costs $0.20 more per gallon. Can running premium when not needed lead to carbon fouling from the slower burn? Short of using a ping sensor / warning system, how can you determine the octane an engine needs?
    Last edited by Rivernut; 08-09-2010 at 08:11 PM.

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    Senior Member lbhsbz's Avatar
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    Quote Originally Posted by Rivernut View Post
    I was told to run 93 octane in my SBC Vortec 5.7. It has about 32 degrees of total timing, stock heads and pistons. Premium costs $0.20 more per gallon. Can running premium when not needed lead to carbon fouling from the slower burn? Short of using a ping sensor / warning system, how can you determine the octane an engine needs?
    What's the compression ratio of your stock motor? If it's less than 9.5:1...I wouldn't waste my money on the race gas...I'd use '87. If you want...I've got a knock sensor setup you can borrow/buy to see what it's doing....has a little light bar that tells you when it's about ready to explode. I know it works....cuz it told me right before I .... nevermind. You might be able to use it though. send me a PM.

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    Senior Member Rivernut's Avatar
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    9.4:1 stock pistons and heads.

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    If you can't afford that extra 20 cents, you can't afford a boat.

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    cfm
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    Quote Originally Posted by Rivernut View Post
    9.4:1 stock pistons and heads.
    Stock GM Marine Vortec will run fine on 87. GM also states this. I prefer to be on the safe side of things and would run 89 if you can, especially if you tune things more to the edge like most of us Hotrodders do to get 'a little more' out of things.

    Quote Originally Posted by GM Marine Website's Literature in .pdf
    Specifications
    2011
    © 2010 General Motors
    www.gmpowertrain.com
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    747.0
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    559.0
    (22.01)
    217.0
    (8.54)
    510.0
    (20.08)
    255.0
    (10.04)
    Type: 5.7L V-8 (Gen 1e Small Block)
    Displacement: 350 cid (5736 cc)
    Engine Orientation: Longitudinal
    Compression Ratio: 9.4:1
    Valve Configuration: Overhead Valves
    (2 valves per cylinder)
    Assembly Site: Toluca, Mexico
    Valve Lifters: Hydraulic Roller
    Firing Order: 1-8-4-3-6-5-7-2
    Bore x Stroke: 101.60 x 88.39 mm
    Bore Center: 111.76 mm
    Bore Area: 648.59 cm²
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    Last edited by cfm; 08-10-2010 at 10:00 AM.

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    Senior Member Rivernut's Avatar
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    Lost Lake is a Whie Trash settlement.

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    I'm No Expert Shaun's Avatar
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    Quote Originally Posted by Rivernut View Post
    Lost Lake is a Whie Trash settlement.
    what?

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    gn7
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    Quote Originally Posted by Rivernut View Post
    Lost Lake is a Whie Trash settlement.
    Quote Originally Posted by Shaun View Post
    what?
    I gather he is refering to a different Lost Lake, in a different state. Based on his avatar. Then again, I am clueless to what Whie even means



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    Cole SS cole ss's Avatar
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    What octane gas should I use on my stock compression 1990 454 and why? Does it help to use high octane on a low compreesion motor? Thanks

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    Senior Member lbhsbz's Avatar
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    Quote Originally Posted by cole ss View Post
    What octane gas should I use on my stock compression 1990 454 and why?
    the cheapest gas you can find. Octane = knock resistance. low compression engines don't need the knock resistance of 87 octane, let alone 91 octane

    Does it help to use high octane on a low compreesion motor? Thanks
    No...it will only make it faster since your wallet is lighter and you're carrying less weight.

  13. #11
    Senior Member MACHINEHEAD1's Avatar
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    Run the 92. I have done what I think is pretty intensive tests on the vortec headed 350. However, these tests have only been done with a carb.

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    Senior Member Rivernut's Avatar
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    Burnt Sticks lists Lost Lake with his idiotic comment. Lost Lake here is carnie-ville. Back to octane discussion- do knock sensors work to help dial in timing, jetting and octane? Do they pick up false sounds of impellers or aluminum hulls banging around in chop? And again- does running a higher than needed octane cause carbon build-up from incomplete combustion?
    Last edited by Rivernut; 08-13-2010 at 08:19 PM.

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    SLOW MEMBER slowboy's Avatar
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    Quote Originally Posted by Rivernut View Post
    B. Lost Lake here is carnie-ville.
    Never been there, but that is funny.
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