90 Octane Ethanol Free or 93 Octane 10% ( hopefully )

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63qcar
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90 Octane Ethanol Free or 93 Octane 10% ( hopefully )

Post by 63qcar »

Finally several stations here have ethanol free hi test pump gas . I have a choice between 90 octane ethanol free or 93 octane with , hopefully , 10% ethanol pump gas .
Car is a Cobra replica with a 482 FE , 10.5 : 1 compression and a fairly long cam . Trying to decide which of the two to use . Currently running on the 10% 93 octane pump gas and wondering what advantages , if any , changing to the none ethanol would be ..... other than not screwing up the carb etc .
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2seater
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Re: 90 Octane Ethanol Free or 93 Octane 10% ( hopefully )

Post by 2seater »

Slightly better fuel mileage if it doesn't knock due to the lower octane.
David Redszus
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Re: 90 Octane Ethanol Free or 93 Octane 10% ( hopefully )

Post by David Redszus »

When a single fuel octane number is presented, it is usually the index or average of the RON and MON octane numbers. And that's a problem; knowing the index octane does not tell us the RON and MON values.

A fuel with an index of 90 could actually consist of 94RON and 86MON.

A fuel with an index of 93 could actually consist of 100RON and 86MON.

While the index octane numbers are different, the MON values are the same. The engine pays far
more attention to the MON values than to the RON or index numbers. Why does this happen?

The 90 index fuel has a fuel sensitivity of 8, while the 93 index has a sensitivity of 14.
The sensitivity is the result of the components used to build the fuel. Fuel sensitivity will tend
to determine if an engine will detonate at high speeds or at lower speeds.

From an enrichment perspective, whether or not a fuel contains oxygen does not matter as long as:
stoich x specific gravity = the same number.
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