Tuning a Mustang to run E85 Fuel can be quite challenging if you're not sure where to begin. It requires the right combination of parts, as well as the proper computer adjustments to feed the extra fuel requirements. There are few tuners that understand what needs to take place with the ECU on your Mustang. We'll try to provide some basic tips here on this page, but the knowledge of a reputable tuner will be far more important in the outcome of your E85 conversion.
Our E85Mustangs.com project car is the yellow 1999 GT you've seen on this site, nicknamed "BrightMare". It is tuned by Pro-Dyno who has spent a tremendous amount of time to understand what makes this fuel tick.
Understanding Air/Fuel ratios
However most AFR gauges you can purchase to display a numerical value of the AFR, are showing you values for gasoline. This is where it can get tricky, and it's important to understand how this ratio works on both gasoline and ethanol-based fuel.
All AFR's regardless of fuel type work off of a common number called Lambda. A value of 1.0 in Lambda represents the stoich for any fuel. Gasoline is Lambda 1.0 at stoich. E85 is Lambda 1.0 at stoich.
If you already have a standard gasoline AFR meter hooked to a wideband O2 sensor, you can still use the displayed gasoline AFRs in determining your engine's true AFR. For example, if your gasoline meter is showing 14.7, then we know this is Lamda of 1.0. The equivelent on the E85 side is around 9.7. Therefore you can conclude that the 14.7 you see on the gauge is a true AFR of 9.7. This allows you to effectively use existing gasoline AFR components or software to tune an E85 Mustang without buying special equipment. Simply use the same target AFRs on your gasoline gauge that you normally targeted for gasolline.
For a late model modular Ford engine, we can tell you that it requires about 20% more fuel at part throttle, and about 40% more fuel at wide open throttle (WOT) so ensure you have adequate fuel flow to the cylinder before you begin. This is where the experience of a professional tuner becomes important to understand just how much fuel to add and when, to make the perfect fuel curve.
SUMMER BLEND VS. WINTER BLEND
The blend changeover triggers a change in the AFR because the ethanol percentage varies from 70% to 85% depending on the seasonal temperatures where you live. 70% ethanol content is the minimum percentage rating for Winter Blend E85. There is a middle grade (class 2) during Spring and Fall with a minimum of 74% ethanol. Summer Blend has a minimum of 79% but all variations are still called E85 for a recognizable common name. This changeover of blends varies per climate (NY goes to Winter Blend much sooner than Georgia). To see the complete chart by state, GO HERE.
The ethanol percentage changes are important to note because it changes the AFR, primarily at WOT when you're in Open Loop mode. (During Closed Loop or part-throttle operation, the O2 sensors report back to the ECU and tell it how much to modify the fuel flow.) How much does the AFR change? Our worst case projected scenario, is 1 full point on your gasoline AFR gauge. This represents the differences between 85% ethanol and 70% ethanol however the actual change between seasons is likely to be less than this. We want to ensure you understand the potential for seasonal changes.
With that said, let's look at what happens when going from one blend to the other... Let's say it's August and you're currently running a Summer Blend of E85 fuel. If your next tank fill-up were to be with Winter Blend, the car will go slightly more rich. At WOT, this is not dangerous, but could cause a performance impact if AFRs are not ideal. How much more rich? Well, that depends on the actual percentage of ethanol in the fuel you purchased.
Let's look at the flip side going from Winter Blend to Summer Blend during the Spring time. What happens here is much more important, because now we are going from less ethanol content (70%) to more ethanol content (85%) and that will potentially cause a lean condition. As we all know, lean is great on your wife or your grilled chicken, but certainly not on an internal combustion engine! As mentioned above, the maximum range it should fluctuate at WOT, is 1 full point on your gasoline AFR gauge. If you were previously at 11.8 AFR with the pedal to the floor, it could potentially go up as much as 12.8, but more likely around half a point at 12.3. When performance tuning, this could be a critical mistake that causes engine failure. The high octane is much more forgiving than gasoline but the longevity of your motor ultimately depends on how safe your tune was built.
During the transition months of Spring and Fall, it's even more difficult to know what class of E85 you're buying and testing your fuel as mentioned above is even more important. For the best results you will need two variations of the tune to load (winter and summer). The SCT Xcalibrator 3 is a great tool for choosing between load files, or the use of an SCT flip chip.
If multiple tunes are not possible, you're better off building your tune with Summer Blend (85%) and letting the car go more rich in Winter, so that you will be right on target again when warmer temps return during racing season.