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Fuel:-Octane rating 

 

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 Post subject: Fuel:-Octane rating
Posted: Mon Jan 22, 2007 2:12 pm 
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Can anyone explain to me what the actual "octane" is in fuel? ie is it a specific chemical?

Also what is it with octane rating causing the effect of pinging in motors. Only reason i ask is i have rebuilt engine which now HAS to run 95 octane or above else i get pinging.

 

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Posted: Mon Jan 22, 2007 2:55 pm 
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ULP : 91
PULP: 95
BP Ultimate :98
Shell vortex :100 (i think 5% ethanol)

some one correct me if im wrong
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Posted: Mon Jan 22, 2007 3:00 pm 
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Octane is one of the many many hydrocarbons that makes up a drop of petrol. c8h18... it has many isomers to it...

Without going into too much detail, the octane rating describes the anti-knock properties of the fuel. The higher the octane, the more resistant the fuel is to prematurely combust when pressurised (i.e. when a piston is thumping it into a cylinder head)

 

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Posted: Mon Jan 22, 2007 3:06 pm 
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Research octane number.

higher octance fuel is less likely to explode when put under pressure, exploding before it is ignited by the sparkplug.

esstentialy cause the expansion of gasses before the piston hits TDC, meaning the gas will be trying to force the piston down, the movement of engine forces it up and it pings.

if you need 95RON then the engine has probably got increased compression.

 

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Posted: Mon Jan 22, 2007 8:09 pm 
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thanks for that 4.9 and gaz. explained it perfectly. Yeah my comp is 9:8:1 so definately needs high octane.....premium dude...premiummmmmmm

 

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Posted: Mon Jan 22, 2007 9:11 pm 
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the new shell fuel has some level of ethanol in it to bring it to the magic 100 mark. e100 fuel is rated somewhere around 114 RON.

i did a big thread on this a fair while ago.

pritty much the petrol companies take a 44 gal drum and put 43 gal of 91ulp in and a gal of octane booster to it. that was what the old optimax was made of. and i think ultimate was for a while too.

 

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Posted: Tue Jan 23, 2007 11:08 pm 
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And diesel has a Cetane number, this is its ability to combust under compression. I thought I'd just put that in if you come across it.

 

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Posted: Tue Jan 23, 2007 11:41 pm 
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cjh wrote:
And diesel has a Cetane number, this is its ability to combust under compression. I thought I'd just put that in if you come across it.


hmmm diesel...still the most efficient combustion engine around ever since it's invention by the diesel dude (forgot his name)

phong =P~

 

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