I ran tests yesterday and today in the mornings (around 7:30 - 8:15 am) with ambient temperatures around 50 F and no wind with regular 87E10 TopTier Mobil ($2.059 per gallon) and with 93E10 TopTier Mobil ($2.599 per gallon).
I depleted the 87E10 tank to a few gallon and ran a test loop of about 45 miles with about 42 miles on I-81. When completed, my MTE showed 21 miles. I put in about 4.5 gallons of 93E10 and drove yesterday after the tests for about 20 miles which should have used up any 87 octane in the fuel line. I assume that I had around a 92 octane mixture in the tank when I ran the second test. I removed my golf bag with clubs and balls (around 20 pounds) in the second test since I likely had around 2+ gallons or more of fuel in the tank on the premium test vs the regular test.
My average I-81 interstate speed was 66.5 and 66.4 mph (including 2 exits to turnaround). The interstate terrain is hilly. I used eco-cruise. There were a few times I had disable eco-cruise and slow down because of traffic and a few times I accelerated moderately to around 70 mph to quickly pass slower vehicles. There was no "aggressive" driving. The overall average MPG and MPH shown on the attached graph is derived from the trip data and thus time includes slow downs and stops at 2 turnarounds and at 2 traffic lights.
Bottom line: spark advance increased significantly using 93E10 over 87E10. But, the slight increase in FE of 0.7% with premium is within the noise of the tests, IMO. See attached graph. The bins used are in 2 degree intervals. Thus, for example, the bin labeled 33 would include spark advance data that is greater than 31 up to and including 33 degrees.
This is virtually the same as I observed in the summer on I-40 with three successive fill ups of premium fuel as I pointed out in the AAA fuel quality study thread. As I said in that thread on spark advance, it appeared the frequency of higher advance increased using premium but I didn't record any data. This test shows that spark advance does increase significantly.
There are a lot of caveats including that we don't know what the specs of the gasoline really are and that these tests should be run many more times. But I have never seen any evidence that supports a significant increase in FE using premium E10 over regular E10. Because modern engines when in closed loop run a stoichiometric mixture of fuel and air, virtually all fuel should be burned. Thus IMO, heating value of the fuel will be the primary determinant of FE of a modern engine designed to burn regular fuel.
I will deplete the 93E10 tank to a few MTE and put about 4 - 5 gallons of 90E0 in the tank and run the test again when ambient temps are around 50F and no wind.
87E10 vs 93E10.PNG 42.44KB 0 downloads
Edited by Plus 3 Golfer, 01 October 2016 - 01:11 PM.