Premium vs. Regular unleaded gas - Page 3 - Mercedes-Benz Forum

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post #21 of 23 (permalink) Old 09-02-2009, 03:11 PM
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I'm assuming "MAP" is Manifold Absolute Pressure.

Although, in this case, "map" is simply a plotting of points on a graph, connected with lines, and various plots are superimposed onto one graph, leaving a bordered, shaded in region which are the operating parameters and values. When one goes one by one, you might have a plot for 91 octane, with the respective ignition, fuel, knock, and a host of other values. That's one kind of map. Then there could be ones for 87, and ones for 85 and bad gas.
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post #22 of 23 (permalink) Old 09-02-2009, 03:17 PM
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post #23 of 23 (permalink) Old 09-02-2009, 04:58 PM
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Here we go again.

Mapping only goes so far; it can change dynamic timing and injection amount and duration (depending on the design). It can't affect basic design.

When you design a combustion chamber, static valve timing and compression ratios for a specified octane rating, you can throw whatever map you wish into the ECU and it's still not going to compensate for the design "flaw" that presumes a minimum octane. You will still have incomplete combustion, hot spots, deposit accumulation (especially if the injectors are dumping in extra fuel to help compensate, which over time will increase the effective compression ratio, compounding the problem) and increased emissions, which will overwork the cats and O2 sensors.

Really, you can use any justification you like for saving a few bucks at the pump, but it's like trying to convince yourself that if you jump from a second story window into a rose garden you're not going to get scratched. Again, what does the manual say? You can use regular in an emergency, but drive like a grandma and get proper fuel as soon as you can. There are reasons for that, but like I always say, one of the great things about owning a car is getting to decide how to maintain it...or not.

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