Ford Mustang Forum - View Single Post - 93 Octane (10% Ethanol) v. 87 Octane (Ethanol free)
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post #10 of (permalink) Old 01-21-2016
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Originally Posted by zinc03svt View Post
It's "best" to go full e85/e70 etc. or stay straight clear pump. Mixing creates inconsistent fuel and or tuning. Are you testing that ethanol content at every fill up? Reason? Because corn has different stoich than regular pump.

Yes, the ecu will correct/compensate to a degree. You need to run logs from the station/s you use for fuel. Your tuner should dial in best he can.
The difference between E10 and ethanol free is less than 5% in fuel volume needed. Your ECU compensates more than that with air temperature changes regardless of the tune. E85 needs around 30% more fuel. That requires tuning.

A tuner will set a baseline fuel map in your tune and then rely on the ECU to monitor and adjust AFR's through the O2 sensor readings. There is a short term fuel enrichment process that will add and remove fuel as needed to keep ratios where it needs to be in the transient short term driving. This happens several times per second. If over a period of time, the engine is always having to add or remove fuel then the ECU will make a long term fuel adjustment to move the baseline enrichment process up or down. A 5% change in fuel AFR's is absolutely zero issue for an ECU to adjust for.

Originally Posted by Thereaper
Larger injectors will fix that. I run 93 with 10% ethanol and it works for me. Why do people make a big deal out of ethanol
Exactly, In modern vehicles (mid 90's and newer) there is zero issue running gas with some ethanol in it. The big deal about ethanol in gas is that when it was first introduced it had the possibility of causing issues in older carbureted vehicles that were still very common in the mid 90's. These vehicles were not able to adjust as easily to the fuel mixtures as fuel injected vehicles and some of their fuel system components would react with the ethanol in the gas. This is no longer the case and newer vehicles have ZERO issues with the percentages of Ethanol in E10 fuels.

E85 is a different story and is much more corrosive than E10 and thus "sometimes" requires changing some components in a fuel system to work properly. They also had to put in bigger injectors, fuel pumps, and fuel lines vs non E85 vehicles (Enter the FLEX FUEL sticker on cars)

This issue was further complicated whenever fuel prices shot through the roof in the mid 2000's and everyone was extremely worried about fuel mileage. It came out that E10 fuel got less gas mileage than 100% gasoline, so everyone again started saying that ethanol fuels were terrible and you should always get 100% gas. Even though 100% gas was costing as much as 15-30% more per gallon than E10 even though only it got about 5% worse fuel mileage. Your driving habits have more affect on fuel mileage than E10 does.

Basically like most stupid things in the world, the bias towards E10 fuels is 100% based on fear and ignorance.

Originally Posted by Blazin72
Good question. A lot people avoid E10 but tuning for E85 is popular. Seems counterintuitive.
If E85 was more readily available near me and I was going to forced injection I would go to E85 in a heartbeat. E85 has octane ratings over 100 and is amazing with forced induction.

Having said all of the above, if your ECU can adjust for higher octane ratings (and ours can) your vehicle will make more power with higher octane fuel regardless of it being 100% gas or E10.

2012 Mustang GT, Brembo Pkg, Yellow Blaze Metallic

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