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View Full Version : Summer vs Winter fuels - Important!




370 HEMI
10-09-2009, 11:38 AM
A couple people that are using ACES IV have recently called me and tried to figure out what is happening with their datalogging. It seems that what once worked for them during the Spring and Summer is now not working quite as well. Some are seeing the same or more KR both ST and even some LT when before they saw virtually none.

Others are sending me pm's asking why all of a sudden their gasoline mileage has gone down some even when using the ACES IV. So with that in mind, I thought it important to discuss it openly.

Many on this forum and really most everyone is actually very unenlightened as to the situation between Summer and Winter fuels, what happens between seasons and why it occurs.

Fuel mileage is subject to many outside factors and unless these factors are accounted for, the answer to the question of why is some knock retard returning and fuel mileage increased or decreased (irrespective of whether ACES IV was used) is cloudy at best. So it may be useful to summarize some of the factors known to affect the situation.

When looking at a real-world applications.....trying to figure out what has caused a difference in BTU and miles per gallon, keep in mind that it is very likely to be a mixture of competing factors



Summer Fuel vs. Winter Fuel: Some will note a decrease in power (more knock retard even at cooler temperatures) and mileage over a period of several months going from summer to winter.

What is not considered is that refineries will vary fuel composition from season to season. Gasolines sold in the summer contain about 3-5% more energy value than those sold in the winter. This means more potential thermal energy content in the fuel with corresponding mileage during the summer and a fuel that will detonate faster and a mileage reduction occur as winter fuel is introduced to your car.

The main reason for the difference is that winter fuels must be blended to be more volatile (in order to vaporize more easily in cold weather for better cold starting) and this means adding more “aromatic” molecules to the blend. This starts usually the last week in August to the first week in September for an October 1st deadline. Unfortunately when the refinery does this (Federally mandated in every state of the country) this lowers the BTU energy value of the winter blend (more KR) at the same time, then less mileage in the winter than in the summer (all other things being equal).

Remember that there is a variation from station to station even in the summer time. The properties of fuel vary much more than most people would think from gasoline station to station and even batch to batch at the same station. While it is true that gasoline and diesel fuels have to meet certain minimum specifications to be sold, this does not stop this variation in specs like energy value (BTU Content) which can produce variations in performance and mileage simply from batch to batch, even at the same station.

During a 2006 fuel survey conducted by the Department of Energy, it was found that the summer fuels sold by the same station and same supplier varied in energy content as much as 3-4% while winter fuels varied almost by 5-7%. Most people who look for reasons behind a reduction in performance and a drop in fuel mileage do not consider that the fuel they are using in a before/after comparison may not have the same energy value, even if they bought it from the same gas station. This is why our cars have a speed density system to help adjust for the variances. However, when we superceed this with a Predator or other "tuning" device, we start to see things change on our datalogging.

Part of the issue is the Federally mandated “reformulated” gasolines (RFG) which are fuels that have oxygenates added to them, such as ethanol. At one time we used something called Methy Terciary Butyl Ether or MTBE, but that has been banned for use in motor fuels due to ground water issues. An oxygenate will be added to gasoline to increase the oxygen content of the fuel for the purposes of reducing environmental emissions. However, these gasolines are becoming mandatory in virtually all states originating from California.

While they are relatively better for the environment, the addition of an oxygen-rich substance to gasoline means the total BTU energy value of the fuel is less and sometimes far less, which means reduced performance and your mileage will definitely be reduced as well.

A gallon of RFG will contain up to 5 % less energy than a gallon of conventional fuel (which are virtually unavailable with the federal mandate that came in at the end of 2007. This difference will be most pronounced in the winter, when the gap between conventional fuel and RFG is the greatest.

So when datalogging, it makes it much harder to nail down...especially with CARB fuels in California.

You see, the problem is you want more high performance in your car in a time where they are making the fuels with lighter content and less rich components leading to your inability to push it where you would want to. The Powers that Be think you should be driving a hybrid or a plug-in electric etc.

The result is that whenever you start trying to use these winter fuel blends in a performance application, they start to thermally clip and do not extend or resist detonation as well and the burn isn't completed evenly though it still specs out as 89 or 91.

This is also the same with the Diesel Fuels. This is the main reason we do not do evaluations of the ACES II Diesel Fuel Formula during winter months anywhere in the country.

My suggestion is if you are seeing more KR step up one fuel grade during the winter and continue to use the ACES IV as normal. Depending on the gasoline, some may have to run their cars on 91+ ACES IV and in certain circumstances, even on an 89 tune if necessary and see how that works for KR and fuel mileage. Remember this is from October 1st to really the middle of April. Knowing up front what is happening will help guard against a potential problem and full disclosure really helps everyone!

The point is that ACES IV is blended the best it can be for year around use, it is simply that the fuel target changes with the refineries constantly and there is a limit of what our product can do with poor gasoline on any performance application. :bigthumb:

Regards,
Brian
BND Automotive LLC:driving:
440-821-9040




GoofyTimL
10-09-2009, 02:52 PM
So more ACES IV in "winter" isn't really a solution either... right?

mnunes
10-09-2009, 10:14 PM
Brian, that completely explains what I'm seeing now in my logs. I think I'll be moving back from 89 to 91 for the winter.

The Powers that Be think you should be driving a hybrid or a plug-in electric etc.
Kill me. Just kill me now.


So more ACES IV in "winter" isn't really a solution either... right?
My guess is that there's only so much that ACES IV can do, and it's going to be more dependent on the fuel itself. Also considering the difference in price between adding more ACES IV or going up one grade of gas, I think that it's impractical to use more ACES IV to compensate for the winter fuels.

wickedchargerrt
10-09-2009, 10:49 PM
People also need to realize its harder to combust cold fuel. Gas mileage is always down in colder temps due to the pcm throwing more fuel at the car due to the temp seen by the iat. this is the same trick those stupid IAT FOOLERS that they sell on ebay do by relocating the iat to a colder spot it richens up the mixture.
A normal drop of 2-3 mpg is average if you live in states where temps can go below freezing in the winter.
People also forget they let their cars warm up a lot in the winter. TOo may people are under the impression your car loses very little gas at idle and gets "good mileage" . thats actually completely false. Remember although your car doesnt use a lot of gas at idle you are getting 0mpg, since the vehicle isnt going anywhere.
I put in a ton of remote starts at a part time job this time of year and people that actually use them easily drop 3mpg in the winter.

370 HEMI
10-10-2009, 08:56 AM
So more ACES IV in "winter" isn't really a solution either... right?

Tim,

You and mnunes is right. There is a law of diminishing returns here as the bell curve on the ACES IV is very narrow. You get the best bang for your buck (no pun intended) with 1 oz per 6 gallons. I have had customers try 1 oz per 3 gallons with some success but to mnunes point, at what cost!

Better to go up 1 pump grade during the winter and see how things are and then go from there. It is a bane we have to live with 6 months out of the year....unless we want to spend 8.00 a gallon for unleaded racing fuel etc.

Thought everyone would want to know. :beerchug:

Thanks
Brian
BND Automotive LLC:bigthumb:
440-821-9040