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Old 01-30-2013, 07:02 PM   #45
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Originally Posted by mishka View Post
Is there any way to get the normal (non-winter) gas? I rarely start driving on a cold engine.
On that note, it takes almost 5 minutes for the engine to warm up in this 25 degree weather. Is it better to drive it cold since i'm not getting any "mpg" while sitting there at 0 mph? Or should I warm it up like I have been doing? I thought that colder engine uses more gas.
Yeah it's not a rotary or from the 1920's. The only requirements for driving are turning the engine on, and putting it in gear. I would disengage the parking brake too, but to each his own. Maybe give it five seconds to get the oil moving around the block if you want.

Originally Posted by Roadworthy View Post
Here is an interesting idea:

Those who have a 2012 TI or I think virtually any 2013 that is designated as being able to use E85, I think they are tuned to scale better with higher octanes. E85 from my understanding has a much higher anti-knock rating, hence why people throw it in for race applications. The big requirement for engines to use E85 from what I remember is high pressure (Direct injection) and a tune that can scale the ignition timing higher to take advantage of the higher anti-knock properties, hence more power!
Correct, ethanol has higher anti-knock properties. It has a higher effective octane rating (some quick research shows it is around 94 - 96 [(R+M)/2]) as a result. The difference is energy density. Pure ethanol has an energy density of 77,300 BTU/gal. If you use a 114,000 BTU/gal base fuel (typical for ethanol free summer fuel, some ethanol free winter fuels may reach this level), E85 will only provide 82,805 BTU/gal, which is about a 27% reduction (hence the estimate you see around that E85 reduces fuel economy by about 30%).

So, E85 increases the octane rating but it has less energy. How do you make more power on E85? You use a crap ton of it. You up the injector size and cram it in there. Say goodbye to any fuel economy you may have had in the first place.

I found a pretty awesome paper talking about gasoline and ethanol that pretty much covers all of the topics mentioned in this thread and pretty much every other gas thread. I recommend every give it a read, it's very informative. It is also where I got my data for the reply above.

Changes in Gasoline - The Auto Technician's Guide to Spark Ignition Engine Fuel Quality
2012 Focus SE Hatch 5spd sport package, Tuxedo Black Metallic
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