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Location:
Perth
Registered:
May 2004
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Effective Compression Ratio / Octane rating
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Wed, 04 May 2005 08:26
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Hello there,
have been doing some reading about "safe" effective compression ratios.
for those that dont know what it is, go here www.google.com.au
Most of the sites i find are in america and thus refer to use of 92 RON fuel.
They state that for an engine running 92RON and a
Roots type SC - safe ECR = 12.5:1
Centrifugal SC? - safe ECR = 13.5:1
now to my question,
What effect would an increase in OCTANE rating of fuel used have on lifting the safe ECR level? Would the increase be significant?
Cheers,
Adam
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Registered:
June 2004
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Re: Effective Compression Ratio / Octane rating
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Wed, 04 May 2005 08:37
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hey i didnt think that it would have any effect on your comp ratio.
i do know that the higher the octane rating the slower the fuel burns..
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Location:
Perth
Registered:
May 2004
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Re: Effective Compression Ratio / Octane rating
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Wed, 04 May 2005 08:50
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Effective Comp Ratio = ((Boost / 14.7) + 1) * Mech Comp Ratio
Yes octane has no effect on mechanical compression ratio.
effective comp ratio is NOT the same as Mechanical Compression Ratio.
Octane level does effect what level of ECR is deemed safe (ie before there are troubles with detonation / tuning etc)
Just was wondering how much a difference running 95RON or 98RON would make to the "safe" level.
Cheers,
Adam
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Location:
Lost in the K hole
Registered:
May 2002
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Re: Effective Compression Ratio / Octane rating
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Wed, 04 May 2005 11:26
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first up, americam fuel isnt rated 92RON its 92OCTANE... an average of the fuel's MON and RON ratings. Aust fuel states RON only, and we never know what the MON or average are (which is my theory underlying the differences in 98RON fuels)
secondly, the number you should REALLY be chasing is the DYNAMIC compression ratio, not just the effective... you need to look at you cam timing and duration, as well as boost and swept capacity etc...
once you figure that out, look at the peak cyl pressures, look at your combustion chamber design, your squish etc etc and figure out where youre ignition point is going to be for your fuel
i suggest searching eng-tips, and performance forums
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Location:
Perth
Registered:
May 2004
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Re: Effective Compression Ratio / Octane rating
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Wed, 04 May 2005 13:59
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right, will do and will get back here sometime with some more specific queries 
cheers.
Adam
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