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Old 03-25-2010, 05:30 PM   #11 (permalink)
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An engine can still knock with a knock sensor but the knock sensor prevents it from knocking more than that until conditions change. With a knock sensor the octane doesn't affect engine life as much as it affects power. Current Generation Premium fuel engines will run on less than Premium but their power output is less. Without a knock sensor running too low of an octane fuel will kill an engine before a high octane motor.

The only thing I can believe he is referring to is a little understood event when a high octane fuel(like alcohol) is used in a low compression engine and the timing is retarded past a certain point. The idea is that the fuel may ignite into the exhaust stroke before it completes combustion and damage may occur. In this case I'm speculating but some of this may have to do with lean fuel-air mixtures which reduce flame speed. Engines that try to run alcohol may retard under, I forget what it's called when this happens, but it actually makes it worse. I actually believe that an alcohol motor needs to have more timing advance when it's run lean.

And with that I doubt he has any idea of what he is talking about. Recommended octane is a minimum value. Going a few octane higher will not lead to shorter engine life. Running unleaded Race gasoline in a motor isn't going to kill the motor from high octane. Unleaded Race Fuel only goes to 99-103 octane anyway.

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Old 08-29-2012, 08:21 AM   #12 (permalink)
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I have advanced the timing on my cars engine to get a little more oomph and to get rid of the stuttering and knocking it gets with low octane fuel (93 RON is the lowest available here)

Good thing 95, 97 and 100 RON gasoline is readily available at gas pumps throughout the city.
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Old 08-29-2012, 09:46 AM   #13 (permalink)
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What nonsense did I write!?

Anyway, advancing the timing will raise the octane requirements. What you're doing is raising the dynamic compression ratio and it will probably knock worse on the 93 RON crap, that's about 87 AKI octane if I remember correctly.

Just a bit of an addition, I've found some newer cars that require regular will run better on Premium. For example the new 3rd Gen Ford Focus only requires regular 87 AKI octane but it says in the manual that it will run smoother and better on premium. Which also means it should run a bit better on E85 since the 2012.5+ MY is FFV. But the only guy I know running E85 in a '12 Focus is getting about the same efficiency as Gasohol. Average for the new Focus seems to be around 32 MPG on Fuelly so it's not terrible but he's done 42 or so with Gasoline.

The Honda Fit might be one of those too but I need to verify first.

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