Octane Thoughts?
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Octane Thoughts? - 3/19/2008 8:22:46 PM
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Jst4fun
Posts: 97
Joined: 8/15/2007
Status: offline
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Hello all,
I know this topic has been beat to death, but...
Called the dealer today, he asked what grade fuel I was running, I replied "premium 93 octane".
He then proceeded to explain the higher the octane the slower the burn (which I knew) which in turn leaves larger carbon deposits on the top end.
Dealer suggested numerous times 89 octane!
Said many of thier cutomers run it and have never had problems.
What gives? The price to me doesn't make a difference, Iam concerned about predetonation (pinging).
The dealer even went so far as to say my fuel consumption may go down.
Sure someone has thoughts on this 
Regards,
Nick
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RE: Octane Thoughts? - 3/19/2008 9:16:45 PM
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geotrash
Posts: 277
Joined: 7/9/2007
From: Erie, CO
Status: offline
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Detonation margins are moderate in these engines and there are knock sensors on the block to retard the ignition timing if knocking is detected. That said, most people report WORSE fuel mileage on lower octane fuel because as the knocking increases with power output, the ignition timing is progressively retarded to compensate, even if you can't hear it, affecting power output and combustion efficiency. If anything, the carbon problem will get worse as a result of lower octane fuel.
In my studied opinion (I have done quite a bit of research on the effects of octane and mixture management in aircraft piston engines), your dealer is giving you bad advice. He is also claiming more knowledge of the detonation margins and fuel needs of the engine than the engineers who designed it. No car company will list a requirement for premium fuel if it's not expressly needed because it raises the operating cost of their vehicles- an important metric for consumer evaluations.
Cheers,
Dave
_____________________________
'04 Land Rover Discovery S - Pretty much stock everything - 40K miles
'05 Mini Cooper S - 45K miles
'99 Isuzu Rodeo LS 4WD - 131K miles
'64 Cessna 182 - IFR, STOL
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RE: Octane Thoughts? - 3/20/2008 4:48:22 AM
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Luv2Disco
Posts: 77
Joined: 2/1/2008
Status: offline
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You said you talked to the "dealer". Who did you actually talk to? If this person is correct then why do they sell Premium gas...so we can feel good about ourselves? I have always burned Premium in my Disco II, but I once experimented on a cross-country trip with using Regular vice Premium in my BMW motorcyle. I obtained lower milage per tank using the Regular gas.
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