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Thread: Octane levels

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    Default Octane levels

    What octane level do you run on single seater race boats?
    Pump is 87 and approx 33:1 oil mix
    but if you use something ACES IV-2S Two Stroke Gasoline Formula which bumps it up to Octane 96 - what is the oil mix then
    would this do any damage or any good - would you have to change / do anything else to run at 96
    Talking about Yam 70 CES or Johnson Stinger 75

    Keanaz

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    Team Member DeanFHobart's Avatar
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    Quote Originally Posted by Keanaz View Post
    What octane level do you run on single seater race boats?
    Pump is 87 and approx 33:1 oil mix
    but if you use something ACES IV-2S Two Stroke Gasoline Formula which bumps it up to Octane 96 - what is the oil mix then
    would this do any damage or any good - would you have to change / do anything else to run at 96
    Talking about Yam 70 CES or Johnson Stinger 75

    Keanaz
    What is the compression ratio of those motors? Going from 87 to 96 would not improve your performance I do not feel. Also, 33:1 oil ratio seems a little lean on oil. Do those motors have rod and wrist pin ‘caged roller bearings’ or ‘individual needle bearings’? That will determine you gas / oil mixture. ‘Individual needle bearings’ require more oil. Check with your motor manufacturer or dealership. The octane rating should not have any impact on gas / oil ratio mixture.
    Dean Hobart

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    Team Member zul8tr's Avatar
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    I don't know about the 2 engines noted but on the Mercs and Yamatos I have measured (25ss, 30H, 55H, Yamato 80, 102 & 302) the compression ratio with cylinder volume relative to the top of the exhaust ports (1st gas release location) are in the 5.6:1 to 6.6:1 range, these SSBB engines are certainly not high compression. For the high revs 87 works for me Mercs and Yamatos. I use 16:1 oil mix in the high revers.

    I never saw improvement with higher octane. Also depends where you have the max timing set. The fuel should be quick flame front travel.
    " Three may keep a secret if two of them are dead" Ben Franklin

    Location: SW Orlando, Fl

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    Team Member jon66w's Avatar
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    My Two cents worth! Gas with higher octane levels is accomplishing by adding octane boosters to prevent pre ignition at higher compression ratios. But, they not have any BTU's (Energy) so they are taking up space in a gallon so the lower octane gas will have more energy per gallon than gas with more octane, Simple No?

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    Quote Originally Posted by jon66w View Post
    My Two cents worth! Gas with higher octane levels is accomplishing by adding octane boosters to prevent pre ignition at higher compression ratios. But, they not have any BTU's (Energy) so they are taking up space in a gallon so the lower octane gas will have more energy per gallon than gas with more octane, Simple No?
    maybe, you just need fuel on the edge of detonation, but the more comp the more power all things being equal

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    Running higher octane will let you run earlier timing without detonation.

    We run more oil in the mix. More oil tends to reduce octane levels which can lead to detonation. Higher octane fuel has the same flame speed a lower octane fuel so there is no downside to running it. If you want max power, earlier timing, up to the limit of detonation, is where you get it, so the higher octane gives you safety margin even if you aren't pushing it based on compression ratio.

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    Quote Originally Posted by Yellowjacket View Post
    Running higher octane will let you run earlier timing without detonation.

    We run more oil in the mix. More oil tends to reduce octane levels which can lead to detonation. Higher octane fuel has the same flame speed a lower octane fuel so there is no downside to running it. If you want max power, earlier timing, up to the limit of detonation, is where you get it, so the higher octane gives you safety margin even if you aren't pushing it based on compression ratio.
    the flame speed could well be faster with race gas, but yes avgas for example is not designed for high revs so slow flame front
    Hot rod did a test on fuel years ago with a mild sbc, 9.5:1 ish, the race gas made more power, when on paper the engine didnt need it.

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    " Three may keep a secret if two of them are dead" Ben Franklin

    Location: SW Orlando, Fl
    Thanks LittleCharger thanked for this post

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    love to see a burn test on the oil to see what it does

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