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Guest Message by DevFuse

Get you C-MAX Energi Registered in the official Ford Authorized Registry. More here.

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Apparently nobody mods a C-Max

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103 replies to this topic

#101 OFFLINE   plus 3 golfer

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Posted 27 July 2018 - 05:21 PM

Doesn't the octane rating of premium vary from state to state?   Could be 90, 91, 93 or even 94?     Furthermore how does one know the "amount of additives" found in Premium?   Or, from one brand to another or one refinery to another?   Many unanswered variables that N=1 would have trouble answering. 

"The AKIs of the gasolines offered for sale are set by gasoline refiners and marketers based on their perception of the technical and competitive needs in the market. U.S. and most state regulations do not address AKI minimum values but specify only that dispenser postings accurately reflect the AKIs of the gasolines being sold. The AKI of premium gasoline in some states is higher than it is in others. This is the result of competition. The AKI of all grades of gasoline is lower in the high-altitude areas of some Rocky Mountain states. This is because the octane requirement of older engines without engine control modules decreases with altitude. At higher altitudes, these engines perform as well on the lower- AKI gasolines as they would at sea level on higher-AKI gasolines." - Chevron

But, Chevron states FE is proportional to heating content of the gas not octane as modern engines adjust timing via use of knock sensors.  They also state that premium fuel may have a 1% higher heating value than regular gas. 


With respect to additive, there are many additives: antiknock, demulsifer, inhibitors for oxidation and corrosion and so forth.  In addition there are deposit control additives with a minimum amount required to be added by regulation.  Top Tier gas suppliers have agreed to increase the amount of deposit control additives above Fed. requirements.  One might, therefore, expect better performance (FE) from cars using more deposit control additives than less as there should be less chance of deposits in engines using Top Tier gas.  Regular and premium gas from Top Tier suppliers have the same amount of additives. I only use Top Tier gas.


Lastly, ethanol is added to virtually all gas to meet EPA emissions requiements. The amount as reported to the EPA has been near 10% for many years as the EPA emissions requirements ramped up a higher tier (maybe highest).  So, it's highly unlikely there is much difference in ethanol content in regular and premium from pump to pump (pure gas excluded).


Bottom line: there really isn't any unanswered variables.  Heating content of the gas is the driver, not octane, with respect to FE. 


"Will premium gasoline give better fuel economy than regular?

Will one brand of gasoline give better mileage than another?
Gasolines with higher heating values can improve fuel economy. Mileage differences may
exist, but they will be small compared to the benefits to be derived from the maintenance
and driving tips mentioned earlier.
Traditionally, premium gasoline has had a slightly higher heating value than regular, and,
thus, provided slightly better fuel economy. Its mileage difference, less than 1 percent
better, is not large enough to offset premium’s higher cost. The difference is likely to be
less or nonexistent between grades of RFG.
There can be variance in heating value between batches of gasoline from the same refinery
or between brands of gasoline from different refineries because of compositional differences.
The variance is small, and there is no practical way for the consumer to identify the gasoline
with a higher heating value."- Chevron

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#102 OFFLINE   ptjones


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Posted 28 July 2018 - 11:13 AM


In my testing of premium vs regular I saw an insignificant increase in FE with premium.  See attached chart showing spark advance vs gas type.  Details of the tests are on the hybrid forum - 1 mile stop and go to / from interstate, 40 mile loop at 66 MPH on interstate, temp. 50F.


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.  


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. 



In 2014 Dec.30 I made a record run averaging 68.3 mpg on a tank and then filled up with Regular at run down 7/11 corner store and only got 43.1 mpg on next tank. :( I didn't want to pay the extra $.50/gallon for Premium, that was a mistake.  The previous tank I used Pure Gas octane 89 + NOS Octane Booster which should have raised it up to 91 octane. I suspect the 7/11 Store Regular(87 octane) was old, bottom of the tank and no matter how careful I drove I couldn't get the MPG's I was getting before. :(  I have been watching my timing advance with ScanGaugeII and at 2 Bars acceleration I seem to be running 33 degrees advance.  Going uphill with the rpms going up, so did the timing advance to 37 degrees with high of 41-42 degrees when letting off the gas. Most of the time I have been going 45 mph with some 55 mph. The faster you go, the more timing advance you need. :smile2: I'm going to keep monitoring my timing for a while longer.



Edited by ptjones, 24 October 2018 - 07:06 AM.

#103 OFFLINE   plus 3 golfer

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Posted 28 July 2018 - 02:23 PM

It's really engine rpm not mph since all engine rpm does not drive the wheels as if one is hypermiling and using EV more than just eco-cruising over a route, engine rpm could be greater at a lower mph than eco-cruising.  So, one would likely require greater spark advance if hypermiling because the generator will be charging more frequently and at a higher load (higher rpm).    To see the difference in timing and FE between regular and premium, you need to run a set course at constant speed.   


When I ran my tests, the starting SOC was the same and speed driven to the interstate and on the interstate was set using eco-cruise in an attempt to minimize EV differences.  I don't know whether I still have the data from the tests but I likely recorded engine rpm.  If so, I'll graph timing vs engine rpm for both fuels. This will tell one the difference in spark advance between regular and premium.  My graph does not.  It shows the time spent at spark advance levels.  When I average the spark advance observations, the spark advace using premium is about 5.5 degrees, on average, more than with regular.


I found the recorded data but didn't record engine rpm. One other point when I looked at the records, the octane level in the car for the premium test  was likely near 92.5 octane as I had some 87 left in the tank (less than one gallon) after the regular test which I then blended with 93 twice (about 3 gallons each time) - once imediatately after the regular test and second time after driving about 75 miles that same day. The day of the premium test, I drove about 10 miles to warm up the car which should have purged the first blend out of the lines.


Perhaps in the fall when it's cooler I rerun a similar test and record more data to see the actual difference in timing advance.

Edited by plus 3 golfer, 29 July 2018 - 01:21 PM.

#104 OFFLINE   Wolf


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Posted 23 October 2018 - 04:26 PM

Some of us still need to have a clean and unique vehicle - Just sayin... the fuel economy to me is a bonus :smile2:



Edited by Wolf, 23 October 2018 - 04:32 PM.

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