1997 HP 500 octane reqt
08-03-2010, 03:07 PM
#11
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I have ongoing fuel test with standard pump fuel with 10% ethnol 87/ 89/ 93 octane. The oldest gas to date is 9 months old & 11 % ethnol
Each case the octane is 1 - 1.5 octane higher than what has been printed on the pump. And in successive test I have not had any octane degradation of any fuel in open or seal containers. Test samples are stored both indoors and out. Does not mean the gas won't go bad for other reasons, but it does mean that in 9 months time 0 loss of octane. I started with 93 at the pumps, the fuel tested 94.4 and was tested 9 month later 94.3 octane
Each case the octane is 1 - 1.5 octane higher than what has been printed on the pump. And in successive test I have not had any octane degradation of any fuel in open or seal containers. Test samples are stored both indoors and out. Does not mean the gas won't go bad for other reasons, but it does mean that in 9 months time 0 loss of octane. I started with 93 at the pumps, the fuel tested 94.4 and was tested 9 month later 94.3 octane
08-04-2010, 07:39 AM
#12
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Check out the 'Full Throttle Marine 496 Mag Dyno Testing & Myth Busting' report on Bob Lloyd's Full Throttle Marine web site.
http://www.fullthrottlemarine.com/
He dyno tested 87 vs 93 octane on the same 496Mag motor and found no significant differeance in HP.
http://www.fullthrottlemarine.com/
He dyno tested 87 vs 93 octane on the same 496Mag motor and found no significant differeance in HP.
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08-04-2010, 05:27 PM
#14
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If all we're talking about is octane...
For a given set of engine specs, assuming the timing is optimized to the combustion chamber and compression ratio, the fuel that will give you the most power is the lowest octane short of detonation.
Some chambers like more timing than others, and once you have the *right* timing for the combustion chamber, you start playing with the octane and find the lowest that doesn't detonate, bump it a touch for safety margin - and THAT's your octane requirement for that motor. Unless you dramatically change the load (run a too steep prop and lug the motor) or play with the fuel and ignition curves, you don't NEED to run higher octane fuel.
Weather, air density, fuel ratio, all sorts of things come into play, but bottom line is a Merc 87 octane requirement means 87 octane under normal conditions will run just dandy.
Now, there are a host of different things to consider with low octane fuel versus premium blends. Some like to say that the premium blends have better additives. Maybe, maybe not. Race gas, airplane gas, oxygenated fuels, all sorts of other wild stuff - unless you have motors that need it, deep pockets and transfer pumps, stick to pump gas.
If it makes you feel better to pay more for gas, then by all means, do it. But if Merc stamped 87 min octane on your motor, it means that you can run 87 octane and not worry.
MC
For a given set of engine specs, assuming the timing is optimized to the combustion chamber and compression ratio, the fuel that will give you the most power is the lowest octane short of detonation.
Some chambers like more timing than others, and once you have the *right* timing for the combustion chamber, you start playing with the octane and find the lowest that doesn't detonate, bump it a touch for safety margin - and THAT's your octane requirement for that motor. Unless you dramatically change the load (run a too steep prop and lug the motor) or play with the fuel and ignition curves, you don't NEED to run higher octane fuel.
Weather, air density, fuel ratio, all sorts of things come into play, but bottom line is a Merc 87 octane requirement means 87 octane under normal conditions will run just dandy.
Now, there are a host of different things to consider with low octane fuel versus premium blends. Some like to say that the premium blends have better additives. Maybe, maybe not. Race gas, airplane gas, oxygenated fuels, all sorts of other wild stuff - unless you have motors that need it, deep pockets and transfer pumps, stick to pump gas.
If it makes you feel better to pay more for gas, then by all means, do it. But if Merc stamped 87 min octane on your motor, it means that you can run 87 octane and not worry.
MC
