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  1. #31
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    I was told by a former racer of stock obs that leaded fuel was usually good for up to 200 rpm on the top end over unleaded. Could this have a bearing on Mercs recomendations? Gary

  2. #32
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    Quote Originally Posted by olboatman View Post
    I was told by a former racer of stock obs that leaded fuel was usually good for up to 200 rpm on the top end over unleaded. Could this have a bearing on Mercs recomendations? Gary
    Not at all, because its not true. Merc's recommendations are solely based on the possibility of lead fouling spark plugs. Generally just avoid it if you can

  3. #33
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    Mark75H I agee with you but why does Merc say "leaded or unleaded" recommended for some of their motors? Thanks Gary
    Last edited by olboatman; 10-02-2013 at 07:19 PM.

  4. #34
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    Just to say they felt the lead or not was less important than the octane rating

  5. #35
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    Quote Originally Posted by Mark75H View Post
    Just to say they felt the lead or not was less important than the octane rating
    Makes since. Thanks Gary

  6. #36
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    Quote Originally Posted by MUDSHARK View Post
    Just to clear some things up for myself, since this thread has touched on a few different situations as far as required octane and fuel oil ratios, I have a Mercury Catalog from 1997 with all 2.5 models of High Performance engines and it shows mixing 32:1 for S3000 requiring race fuel, 32:1 for SSS120 requiring 92 octane leaded or unleaded, 32:1 for F1 requiring RACE FUEL, 32:1 for XR2 requiring 92 octane leaded or unleaded, 32:1 for 2.5 SS Drag requiring 92 octane unleaded only, 32:1 for 2.5 Offshore EFI RACE requiring 92 octane unleaded only, For all PROMAX Motors it only says 89 octane Minimum and Variable oil injection, then it gets into the 2.5 EFI 260s with peak HP @ 7500 RPMs, which is what I have, and calls for 32:1 92octane leaded or unleaded. So my question is why do some of them require unleaded only but other can be used with both leaded and unleaded? And why would any one run 40:1 in any 260 or 280? I have an even older catalog like this one that is a few years older that I cant find at this time but I seem to remember it showing a reference to 100LL for some of the engines in it. Not really waiting on any certain response but I felt like adding this in.
    Here is what need to you know:

    1. Stay away from leaded gasoline. It is one of the most disastrous inventions by mankind.
    2. Below 7500 rpm, 40:1. Above 7500 rpm 32:1. The reason is that the fuel curve gets very lean up there, so you need more oil in the fuel to get the same amount of oil per revolution
    Last edited by Markus; 10-04-2013 at 03:13 AM.
    Markus' Performance Boating Links:
    www.toastedmarshmallow.com/performance

  7. #37
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    Quote Originally Posted by MUDSHARK View Post
    Just to clear some things up for myself, since this thread has touched on a few different situations as far as required octane and fuel oil ratios, I have a Mercury Catalog from 1997 with all 2.5 models of High Performance engines and it shows mixing 32:1 for S3000 requiring race fuel, 32:1 for SSS120 requiring 92 octane leaded or unleaded, 32:1 for F1 requiring RACE FUEL, 32:1 for XR2 requiring 92 octane leaded or unleaded, 32:1 for 2.5 SS Drag requiring 92 octane unleaded only, 32:1 for 2.5 Offshore EFI RACE requiring 92 octane unleaded only, For all PROMAX Motors it only says 89 octane Minimum and Variable oil injection, then it gets into the 2.5 EFI 260s with peak HP @ 7500 RPMs, which is what I have, and calls for 32:1 92octane leaded or unleaded. So my question is why do some of them require unleaded only but other can be used with both leaded and unleaded? And why would any one run 40:1 in any 260 or 280? I have an even older catalog like this one that is a few years older that I cant find at this time but I seem to remember it showing a reference to 100LL for some of the engines in it. Not really waiting on any certain response but I felt like adding this in.
    Your right on the 100LL.The Merc catalog from 79 list 100oct LL aviation as the preferred fuel for the race motors.And that was at a time when there was a good supply of 93 non eathanol around.And Markus you may be wrong about the lead,My wife says that single malt scotch,is the worst thing developed by mankind

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