E85 mixtures
How reliable is E85 when it comes to the consistency of the mix?
Do they just mix in any gasoline thats readily available at the time or is the formulation strictly controlled?
That is a very important issue if you are running a high power tune. If you just want a good safe daily driver tune (high 90+ octane fuel) you don't need to worry all that much about it.
E85 can actually have a range of fuel blends depending on where you live and what season it is. Just like pump gasoline E85 blends change with the season.
E85 fuel ethanol content seasonal changes
The recommended dates for changing E85 fuel blends are listed in a chart in the E85 handbook on page 22, which is in the "E85 Fuel Specification" tab.
The Volatility class specifications are broken down on page 10.
Volatility class 1 --- minimum ethanol 79%
Volatility class 2 --- minimum ethanol 74%
Volatility class 3 --- minimum ethanol 70%
As you can see each region has a different start date and recommendation for seasonal blends depending on local weather climate.
Here on the high plains east of the rockies in Colorado we run the class 1 fuel blend from mid June -- mid Sept, run class 2 fuel from mid Sept -- mid Oct and run the class 3 fuel blend from Mid Oct -- mid April, then back to the class 2 blend from mid April to mid June. In short here in Colorado near Denver we are already on the winter blend, but there is latitude in the standard, so the standard only specifies a minimum ethanol content. If it is cheaper for the fuel blender to add more he can. Ethanol content is bottom line driven by local weather conditions, and cold starting problems for local drivers just a gasoline blends are modified to give easier starting in cold weather.
In the Southern part of Texas they would never go to a class 3 blend, and in Wisconsin, they would only have the class 1 blend for about 2 months in the summer. In Florida they would be on class 1 almost all year long and in North Dakota and Wyoming and Montana, they would be on class 3 almost all year long.
If you are running a serious tune and high boost you want to be cautious during the season change periods. I know a couple people with turbocharged imports that test the fuel and tweak their tune accordingly.
If you have a wide band simply watch your AFR's at light throttle cruise, if the blend changes you will see it there as the mixture should be very stable in that light load part of the tune. Perhaps pick a certain rpm and gear and learn what your tune does on each.
As the blend goes to lower Ethanol content in the fall the mixture will go rich as you are running more gasoline in the blend to improve cold starting. This is a safe change in mixture for most folks unless you are right on the edge with your tune and need every octane point you can get. In the spring time as the mixture moves back to higher blends of ethanol it is more dangerous as you will lean out a bit, so be cautious on big power tunes when you first trot the car out for sunny spring run.
The standard gasoline added to the fuel is "natural gasoline", ie just the raw gasoline that comes off the first pass at the refinery, but some dealers may not have ready access to that, and will cut the E98 with normal UL pump fuel to get the right mixture.
E85 will probably like richer mixtures than your max power gasoline blend by a small amount. If in doubt take your max power rich gasoline mixture and fatten it up just a bit.
Max power mixtures on gasoline (if you have enough octane) is usually about 25% rich of stoichiometric mixture. That works out to between 12.5 - 11.8 AFR on most cars. Max power mixtures on ethanol can go as high as 40% rich of stoich. That means on a gasoline calibrated wideband you would see about 11 - 10.5 AFR's. My WRX was very happy at a gasoline calibrated AFR of 11.5 but makes just a bit more power at lambda 0.72-0.76 which is a gasoline calibrated AFR of 10.5 - 11.2.
Hope that helps.
Larry