Doug - your MPG just cannot go from 14.7 to 22 merely by changing the fuel. Think back - did you calculate it properly - what else changed? The 22 MPG sounds right; I am guessing the 14.7 MPG was not correct for some reason.
I thought about the initial reading, but have checked my Sport model against hers, it shows 13.7mpg in town, granted I drive differently
than she does, but other than the body trim, the Sport uses the E55 cladding, the drivetrains are identical & the computer readouts were close enough prior to the fuel switch that a rounding error was negligible. I've run this by a couple good friends that are Mercedes guys, they say it is absolutely possible because of the engine management technology used by Mercedes coupled to sensitive sensor technology. The cars were never built to operate on anything but premium fuel, keeping in mind earlier discussions that octane is octane there is something to the difference of non-ethanol premium and it's blended govt subsidized competitor.
My buddy Greg, (aerospace engineer) says it related to thermal dynamic efficiency of the various fuels, octanes and ingredients, cylinder head design, combustion chamber technology, number of valves, plugs & compression ratio;
I do earn a good living dealing in analysis of numbers (I hold several advanced degrees) factoring 10 digits right of the decimal routinely so I'm fairly certain my math is correct, what I'm not certain of is why are we (tax payers) subsidizing ethanol blend fuels when straight fuel appears to be much more efficient at least in the case of embedded computer laden automobiles.
On the other hand, there has been no noticeable increase in the efficiency of the truck, it still hovers about 15mpg if driven sedately but seat of the pants, it starts easier and is still my favorite vehicle to drive but the Mercedes is simply unbelievable in V8 engine management technology, very efficient. I'm still looking to disprove the hypothesis but I'm becoming more convinced that the change is actual as more mileage per tank piles on the trip odometer. Thanks for the conversation. Take care.