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Thread: Snorkel Delete
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Old 01-09-2013, 12:40 AM   #153
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Location: Clovis, CA
What I Drive: 2012, Grey, Focus SE Sport Package

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Originally Posted by TiStick View Post
His CA 91 isn't much better then our 89, if at all.

+1 on the owners manual part:

Octane recommendations

Your vehicle is designed to use “Regular” unleaded gasoline with a pump (R+M)/2 octane rating of 87. Some stations offer fuels posted as
“Regular” with an octane rating below 87, particularly in high altitude areas. Fuels with octane levels below 87 are not recommended.
Premium fuel will provide improved performance.
Originally Posted by suss6052 View Post
12:1 would be an incredibly high compression ratio on 87 octane if it wasn't for the Gasoline Direct Injection and the twin independnt variable camshaft timing.

The injection of liquid fuel directly into the cylinder cools the compressed air charge and helps to prevent detonation, as well as the variable cam timing retarding the combustion cycle enough to prevent spark knock for the most part. It does this by sacrificing a measure of power and performance that could be gained with advanced spark timing. 91-93 octane fuels are more resistant to pinging and detonation/ pre-ignition and therefore the car can adjust timing accordingly in order to make more power from the same quantity of fuel consumed.
So filling up with a premium fuel would actually improve performance? Meaning the car knows it has premium fuel and adjusts for it?
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