Originally Posted by Warp Factor

No, you can't. The C7 ECM keeps a record of every time a change or flash is made.

Higgs, when you put some gasoline in, and then some E-85 (or the reverse order), how long does it take the two to mix evenly? Presumably, whatever goes in first will go into the driver side tank (where the engine supply fuel pump is) until that side is full, and then the rest goes into the passenger side tank. The "jet pump" in the passenger side tank, which is always pushing fuel to the driver side tank will eventually mix the two pretty evenly, but how long does this take, and might the proportions be pretty far off right after a fillup?

Originally Posted by Toddiesel

Wait... are you saying there are 2 fuel tanks? Are we driving big rigs here?? Naw, but seriously, that's a thing??? How does that even work?

Originally Posted by Warp Factor

No, you can't. The C7 ECM keeps a record of every time a change or flash is made.

Higgs, when you put some gasoline in, and then some E-85 (or the reverse order), how long does it take the two to mix evenly? Presumably, whatever goes in first will go into the driver side tank (where the engine supply fuel pump is) until that side is full, and then the rest goes into the passenger side tank. The "jet pump" in the passenger side tank, which is always pushing fuel to the driver side tank will eventually mix the two pretty evenly, but how long does this take, and might the proportions be pretty far off right after a fillup?

Originally Posted by rflow306

I have an E% gauge that reads from the flex fuel sensor. The mixture % starts to change pretty quickly when you add the opposite fuel that is currently in the tank and according to my gauge stabilizes after 7 to 15 minutes of driving. The flex fuel sensor reads E% of incoming fuel to the High-pressure pump so the ECM ethanol content adjustment is seamless if tuned correctly.

Originally Posted by Warp Factor

Understood.
What I was partly wondering was whether prior to the fuel mixing completely, the E85 proportion might be so high that high-throttle operation would exceed the capacity of the fuel pumps.

Originally Posted by Higgs Boson

the fuel pump's capacity does not depend on the flex fuel sensor reading.

Originally Posted by Warp Factor

Right, but the volume of fuel required is higher with straight E-85, and can exceed the capacity of the pumps, so I was imagining a scenario where prior to being mixed with the gasoline to get E-40, the fuel pump might be drawing nearly straight E-85, and not be able to supply adequate fuel.

I think rflow answered my question, that the gasoline and the E-85 seem to be sufficiently mixed in about 7-15 minutes of driving.

Originally Posted by Higgs Boson

maybe if you leave gas stations like a bat out of hell, lol.

Originally Posted by Warp Factor

You don't?
I was actually thinking of something more like filling up at a racetrack, and how much time it might take to get the two fuels adequately mixed before making a full power pass.

Originally Posted by Pacembellum

Originally Posted by Toddiesel

Well that works for me. I'm getting it dynoed in the morning for a baseline, so I'll go ahead and order a flexfuel hit and CAI and then do a dyno tune and post the results so people know the difference.

Originally Posted by Fastmikefree

Hi, did you get a chance to evaluate the 'base' solution with just the flexfuel kit + CAI without a tune vs the same + tune? I am very interested to get your feedback? Thanks

Originally Posted by Toddiesel;1596646031 I've been doing research and I'm coming across some info saying you need bigger injectors and a beefier fuel pump due to the fact that you have to use a lot more ethanol than gas to get the same efficiency.[/b

You will need to boost the capacity of the low side fuel system if you want to run much E-85. Running full E-85 is going to require major changes to the fuel system. This is the reason for using a meth injection system, as advised by Billy, to supplement the fuel system. Meth is a high octane ethanol fuel which will extend the capacity of the stock injectors because it is injected into the intake system separately. The DSX flex fuel sensor system will automatically compensate for the % E-85 you are running. I would not recommend running E-85 unless you are willing to upgrade the low side fuel system.

In my case on my 2016 A8 running a single nozzle meth injection with a low side fuel pump upgrade & stock injectors I am able to safely run 50% E-85 with 93 pump. The HP improvement for using the 50% E-85 is 40 RWHP.


Having said that, I've also seen info where things like the DSX bolt on flexfuel conversion kit will allow the ECM to adjust as needed and makes it sound like no additional upgrades (aside from a tune) is required. If not, how much extra power do you get with just a tune? I'm planning on adding a CAI and probably a lower pulley as well, but I'm more focused on what the flexfuel conversion can do and what it requires right now. Any info would be appreciated!

Originally Posted by jstewart

A tune, low side pump upgrade at a minimum if you want to too get a decent HP & TQ return . With just a tune and the DSX I am not sure how much E-85 you can run and what to expect in gains safely. One other thing you are going to need is a gauge readout for the ethanol % you are running so you do not exceed the safe % established when the car is tuned. One of the competent tuners on the forum like Billy can probably answer what to expect with just a DSX and a tune.

Originally Posted by Toddiesel

The way the tune has been broken down for me is as follows:
E85 requires 2 tunes. 93 Octane tune first, followed by removing fuel and adding E85 (multiple changes required to get ethanol content to 75 - 80% blend concentration), followed by E85 tune. After that, they then have to set up the flex fuel blend parameters so that the you can run any concentration of ethanol content from e10 - e80 and verify safe fueling and ignition parameters.