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Location:
Perth
Registered:
November 2004
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engine timing with 98RON
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Sun, 20 March 2005 05:35
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I have started using 98RON fuel recently and i have realised that its much better performance then ordinary 91/92RON fuel. But whenever i step on the accelerator there is a heap of unburnt fuel and a bit of oil that jumps out of my exhaust. I dont know what it could be except for engine timing. Maybe the exhaust valve opens too early and the combustion stage doesnt have enough time to burn the fuel properly, so the unburnt fuel just runs out of the exhaust.
Has anyone changed their timing after running 98RON fuel? Does it help with this situation?
thanks 
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Location:
Adelaide
Registered:
July 2002
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Re: engine timing with 98RON
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Sun, 20 March 2005 06:31
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higher octane allows more timing advance before detenotation (pinging)
what i used to was run a couple of tanks of premium to make sure i had got rid of all teh 91 octane fuel then i would adjust my timing untill i could hear it start to ping then back it off about 2 or 3 degrees. for example i was running about 13degrees of advance on the 4age.
HTH
cheers
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Location:
Perth
Registered:
November 2004
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Re: engine timing with 98RON
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Sun, 20 March 2005 09:24
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cheer's, ill have a play around with the timing soon and see if i can get rid of the raw fuel spitting problem.
thanks mate
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Location:
Wollongong
Registered:
November 2004
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Re: engine timing with 98RON
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Sun, 20 March 2005 10:07
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A higher octane fuel, takes a higher temperature, and a longer duration to ignite properly...
When you first hit the gas, if the car is EFI, you will have an "acceleration" injection (Don't worry about that)
But when this happens, basically for a split second some more then usual fuel is injected to counter act the extra air, but with your timing, the fuel is not having enough time to burn that extra amount completely out...
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Location:
Campbelltown
Registered:
November 2003
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Re: engine timing with 98RON
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Sun, 20 March 2005 10:47
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wouldn't a higher octane fuel actually ignite at a lower temperature think about it, there is more octane molecules thus there is more active ingredients which would mean it would ombust earlier.
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Location:
Perth
Registered:
November 2004
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Re: engine timing with 98RON
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Sun, 20 March 2005 11:16
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| Kyosho wrote on Sun, 20 March 2005 21:07 |
A higher octane fuel, takes a higher temperature, and a longer duration to ignite properly...
When you first hit the gas, if the car is EFI, you will have an "acceleration" injection (Don't worry about that)
But when this happens, basically for a split second some more then usual fuel is injected to counter act the extra air, but with your timing, the fuel is not having enough time to burn that extra amount completely out...
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yeah thats what i thought would be the problem too, the fuel doesnt have enough time to burn and then exhaust valve opens too early and lets some of the raw unburnt fuel out.
but maybe its something else :S
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Location:
townsville NQLD
Registered:
February 2004
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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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Location:
Wollongong
Registered:
November 2004
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Re: engine timing with 98RON
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Sun, 20 March 2005 22:19
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Our "higher octane" fuels are a longer chain, yet they are more "compact" and actually harder to get to ignite...
When you try to ignite them, they take a higher temperature to actually get them to properly ignite.
Once they have ignited, it takes longer to get it to all completely burn because of the molecule design.
For this reason, more timing is needed, and also, detonation and pinging is avoided more.
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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 22:44
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| Kyosho wrote on Mon, 21 March 2005 09:19 |
Our "higher octane" fuels are a longer chain, yet they are more "compact" and actually harder to get to ignite...
When you try to ignite them, they take a higher temperature to actually get them to properly ignite.
Once they have ignited, it takes longer to get it to all completely burn because of the molecule design.
For this reason, more timing is needed, and also, detonation and pinging is avoided more.
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are you sure it's a much higher "ignition" temperature or "auto-ignition" temperature?
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Location:
Perth
Registered:
November 2004
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Re: engine timing with 98RON
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Thu, 24 March 2005 02:49
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hey all, i timed my engine to about 13 degrees today, i hope thats right  shes a bit better fuel economy too thanks all
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