View Poll Results: What grade gasoline do you use in your 924/44/68?
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What grade gasoline do you use in your 944??
#76
Rennlist Member
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I've run Regular (generally "enhanced" with ethanol) with as low as 86 continuously for the last 4 years with no ill effects. The highest octane you can buy here is 91. Ocassionally I run Mid or even Premium for the additives, and notice no difference in performance.
I didn't notice any difference when I drove it back to the midwest (elev. ~600') last summer, and still used Regular, which is generally 3 point higher octane rating back there.
#78
Nordschleife Master
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Like you, I'm at mile-high altitudes, which allow you to drop the octane used by 2 - 3 points, minimum. You can take 20% off the published C.R. due to altitude. Power loss is also about 20% due to lower oxygen content in the air and the lower C.R.
I've run Regular (generally "enhanced" with ethanol) with as low as 86 continuously for the last 4 years with no ill effects. The highest octane you can buy here is 91. Ocassionally I run Mid or even Premium for the additives, and notice no difference in performance.
I didn't notice any difference when I drove it back to the midwest (elev. ~600') last summer, and still used Regular, which is generally 3 point higher octane rating back there.
I've run Regular (generally "enhanced" with ethanol) with as low as 86 continuously for the last 4 years with no ill effects. The highest octane you can buy here is 91. Ocassionally I run Mid or even Premium for the additives, and notice no difference in performance.
I didn't notice any difference when I drove it back to the midwest (elev. ~600') last summer, and still used Regular, which is generally 3 point higher octane rating back there.
#79
Addict
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I run premium because when I first ran regular, I thought I could hear the engine pinging. The PO had the head rebuilt after the timing belt broke, so I was thinking perhaps the shaved head required the higher octane.
#80
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Not true. Oxygen is heavier than nitrogen, so it sinks. It is 21% at sea level, 16% at 9,000 ft. In Denver or Albuquerque, it is around 18%.
#81
Nordschleife Master
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There are fewer molecules of atmosphere in a given space at higher altitude. The decrease in % is true for both nitrogen and oxygen, at higher altitudes.
So, if you want to say there is a less percentage of oxygen per cubic meter at higher altitude, you would be correct, because there IS less oxygen, but there is also equally less every other gas in the atmosphere. If you wanted to say there is less oxygen per nitrogen content, you would be incorrect. The ratio between the 2 is a constant.
EDIT...This is the most "official" link I can find right now. http://www.altitude.org/why_less_oxygen.php
Last edited by m73m95; 04-27-2012 at 04:29 PM.
#82
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Likewise, I can't find an online authority, but in design of gas-fired equipment this is a correction made. It has to do with the partial pressures of oxygen, nitrogen, and other gases.
Another page on the site you linked says just the opposite!
Another page on the site you linked says just the opposite!
#83
Instructor
Join Date: Oct 2007
Location: John's Creek GA
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That's the great thing about Google! "Oxygen is higher percentage at altitude" versus "Oxygen is constant regardless of altitude" both yield results. Everyone's right!!!
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#85
Three Wheelin'
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93 Octane with no alcohol
Only a few places that sell it here in Nashville/Franklin but like Joe, my 944 is wide open 90% of the time. Carry 42 gallons to the track every weekend and use it all.
Plus the foam in my fuel cell doesn't like alcohol so I either have to drain the cell after every race weekend or use my good gas.
My boxster gets a calculated 2.3 MPG better fuel mileage when I use the no alcohol gas.
Only a few places that sell it here in Nashville/Franklin but like Joe, my 944 is wide open 90% of the time. Carry 42 gallons to the track every weekend and use it all.
Plus the foam in my fuel cell doesn't like alcohol so I either have to drain the cell after every race weekend or use my good gas.
My boxster gets a calculated 2.3 MPG better fuel mileage when I use the no alcohol gas.
#86
#87
Nordschleife Master
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The partial pressure is the pressure a gas would have if it were alone in a volume. The TOTAL pressure is the partial pressure of all the gasses added together. So, when compressing the entire atmosphere's gasses together, the partial pressure of each individual gas will vary from one to the other, because each gas' molecules are different sizes, and can pack together differently.
But, unless you are doing something under extreme pressures, or need to be very precise with your gas mix, the difference is negligible. To a car engine, which just uses atmospheric pressures that vary only slightly on drivable earth, there is next to zero difference in oxygen content. If the equipment you work with depends on an exact gas mixture, then you would factor in the partial pressure of each gas.
#88
Rennlist Member