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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: engine timing with 98RON
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Sun, 20 March 2005 12:31
 
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i think it's more to do with the higher octane fuels burning slower.
best power/torque occurs when the peak cylinder pressures are X degrees ATDC. the only reason you change advance is to match the fuels burn speed to get peak pressure at that angle.
the "octane" used for the rating (i believe) is 2,3,4 trimethyl Pentane. not octane per se. octane rating is simply a measure of detonation resistance.
the 'higher octane' fuel we get simply means it has a higher proportion of MORE BRANCHED fuel molecules regardless of wether the molecule has 8 carbons or not... since the more the branching, the more evenly it burns and the less likely it is to break molecules prematurely (ie detonation)
so basically, you need to advance timing because the higher branched molecules in high octane fuel burn slower and it takes more time to generate peak cylinder pressures..
fwiw, nitromethane requires around 60 deg advance....
anyway, it's late but it's something like that..
oh, and as for avgas, it has a "high octane rating", so it is designed to be highly detonation resistance (hard to shut down a plane motor thats pinging while flying..) BUT this also means it has a slow burn rate, which in turn is why ppl run much more adance with avgas... BUT, thi salso means that a high rpm motor may not get as much benefit as a low rpm motor, sinc eyou may not have enough time for an effective burn at high rpm..
aaaanyway..
Cya, Stewart
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| | Subject | Poster | Date |
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engine timing with 98RON
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gorgan | Sun, 20 March 2005 05:35 |
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Re: engine timing with 98RON
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Hunty | Sun, 20 March 2005 06:31 |
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Re: engine timing with 98RON
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gorgan | Sun, 20 March 2005 09:24 |
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Re: engine timing with 98RON
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Kyosho | Sun, 20 March 2005 10:07 |
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Re: engine timing with 98RON
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gorgan | Sun, 20 March 2005 11:16 |
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Re: engine timing with 98RON
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Corona RT142 | Sun, 20 March 2005 10:47 |
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Re: engine timing with 98RON
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brett_celicacoupe | Sun, 20 March 2005 11:29 |
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Re: engine timing with 98RON
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oldcorollas | Sun, 20 March 2005 12:31 |
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Re: engine timing with 98RON
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Kyosho | Sun, 20 March 2005 22:19 |
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Re: engine timing with 98RON
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oldcorollas | Sun, 20 March 2005 22:44 |
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Re: engine timing with 98RON
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gorgan | Thu, 24 March 2005 02:49 |
