Quote:
Originally Posted by AzNightmare
In theory, I assume the Shell 93 should have worst mileage eventually since ethanol burns faster.
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I always thought that way, but the change isn't that bad if you do the math.
Eth has 76100 BTU per gallon whereas gas has 114000, which gives us ~66% of the energy density. If you run straight eth then yeah it's gonna suck, but we are talking about a mix here.
Keep in mind at the pumps it's not a guaranteed 10% ethanol mixture, it's UP TO 10% so it's at worse 3-4% lower fuel economy, but potentially the damage is less than that depending on that batch of mixture.
My fuel usage gauge on the M3 ticked up from 13.2 to 13.3 after 3 tanks of 93 fvs using the no eth 91. The car drives a lot better though(it may potentially be related to the cooler temperatures as well)
The fuel usage on my X3 ticked up as well from 12.5 to 12.6, but I saw no butt dyno differences in drivability so that's going back to 91.