Quote:
Originally Posted by mahout
Around here this weekend regular is $2.49 and premium $2.69 per gallon.
Thats 8% increase in cost. In places its 30c per gallon more, or a 12% penalty. The difference between 32 and 34 mpg is 6%.
When you spend 8% more for gasoline to gain 6% in mpg, that isn't worth the money.
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Engineer you may be, but an economist you ain't.
That is misleading math you're doing there. What you want to determine is dollars per mile.
$per gallon, $2.49: divided by miles/gallon, 32: equals $0.078 per mile
$per gallon, $2.69: divided by miles/gallon, 34: equals $0.079 per mile
Not much difference -- or is it? Let's toss some miles in there so the numbers get bigger.
10,000 miles at $0.078 per mile equals $778.13
10,000 miles at $0.079 per mile equals $791.18
Still not much difference. The fact of the matter is that the cost of gasoline is a relatively small portion of the total cost per mile to drive a car. By far, depreciation is the greatest cost, followed by fixed costs such as insurance and maintenance. Next comes gas, followed
very closely by interest on the car loan (if gas was $2/gallon, interest on the loan would be higher).
Bottom line: using the cost difference as a reason to use 87 octane instead of 93 octane doesn't really add up. And if you really, really want to save money on driving, buy old cars that don't depreciate and pay for them in cash.
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And true premium does burn slower, which is why static timing on premium fueled vehicles are more advanced than regular fuel specifications. But unless those premium fuel specified vehicles (BMW etc) are programmed to advance further unless spark knock is detected no advantage is gained but hp is. . Few cars specifying regular fuel have that programmed simply because the gain in hp isn't important..
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It's already been shown that the Fit does indeed advance timing further when burning 93 octane than it does when burning 87. However the tests were performed at WOT, so there is still some question as to the benefit of higher octane under normal driving conditions.