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      01-04-2013, 11:48 AM   #17
Red Bread
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Drives: My wife's car
Join Date: Oct 2008
Location: Dallas, TX

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Quote:
Originally Posted by HBWT View Post
Dayum, I like your math much better than mine. I suck at math.
But I refigured it based on today's local prices and 15K per year and 21MPG(lots of in town driving)...so this is a worse case scenario.
87...$3.30
93...$3.60
714 gals

difference of $214.20 per year or $00.01428 per mile
Yeah, I just used the difference in 89 and 91/93 octane, since 87 will almost certainly ding performance and mileage more than the potential savings.

Interesting that this conversation hasn't led to the inevitable discussion of carbon buildup on these engines. Our 2008 N54 was getting to where it needed to be cleaned at 43k miles when we sold it and it was always run on top tier fuels, either 91 in CA or 93 in TX. The N55 and N20 will suffer from the same thing, and since direct injection bypasses the intake valves, no amount of Techron or other fuel additive will help. SeaFoam into the intake or physical cleaning is the only option. We leased this car, in the hope that BMW will follow Toyota/Subaru and others approach with adding a set of supplemental port injectors back into DI designs.