The flex fuel sensor monitors ethanol content and fuel temp. If you have an ecu that can use it, whether the ecu can read the sensor outputs directly or if the ecu can read 0-5 volt inputs(with optional display/converter) than you can change fueling and timing curve with it. It can help with detonation if you change your tune depending on ethanol content. If you have detonation issues this is not going to be a cure all. It can definitely help but not solve all issues.

If anyone local to me would like to see how the flex fuel sensor works,I would be happy to show it in real time.

Cool. I was just wondering if it would detect low octane in the system and pull timing or boost to compensate. Sounds like it could, but not for traditional gasoline.

Does not detect octane just alky content

vary true,,its never mix correctly because you dont know what ratio the last guy mixed it al..i was told it is mixed in tank at the gas station so the octane is never correct..

Probably one of the biggest reasons you don't see more boats running E85 or high alcohol blends is the lack of ECU advancements. Beside the QC4v, the standard Merc ECU hasn't advanced much from the 90's. As mentioned above, to make this all work for the average Joe, the ECU requires a way to know exactly how much alcohol is in the fuel.

While aftermarket ECU's allow you to easily adjust fuel and timing mixtures, some by simply flipping a switch. Modern automotive ECU's have specific tables that adjust these mixtures based off the flex fuel sensor on the fly. These tables can be further refined by software like EFIlive [my favorite] or HP Tuners. So unless your running a flex fuel automotive ECU, you're stuck tuning the engine for a specific blend and sticking to it. No different than jetting a carb. For old school blower and carbs, straight methanol is the long time fail-safe choice.

For everyone considering running E85 in anything, I'd suggest owning the Quick Fuel E85 Fuel Testers available at Summit for under $20.

One other point that often gets overlooked, or misunderstood about alcohol fuels is the BTU and Oxygen content difference from gasoline. While alcohols have lower BTU values [requiring more fuel to achieve same heat], it also caries it's own oxygen molecules. Allowing more fuel to be stuffed in the cylinder and remain stoke. That's like running a shot of nitrous all the time. Why the power potential is always higher on alcohol blends. The Octane value is simply resistance to detonation, but it comes in to play with compression, boost pressures, and timing limits. Potential Power...

Below is the official ASTM BTU chart that breaks down common fuel values. At first glance Ethanol / Methanol looks like a big loser based on BTU's alone. But the truth is those extra attached oxygen molecules pay off big time in the combustion chamber. If that doesn't convince ya to check it out further, remember E85 burns cleaner, has lower emissions, and the majority of your fuel $ goes to midwest farmers vs middle east oil barons...

http://www.afdc.energy.gov/fuels/fue...ison_chart.pdf

I am bumping this back up. Any further advancements with flex fuel marine applications out there? I know that Holley EFI has flex fuel available now. The power gains on this stuff is simply amazing for blower applications. Also, I know for fact it doesn't take an extremely high mix to achieve the benefits. In my CTS-V we converted it to flex fuel (DSX kit as mentioned previously). It is aggressively pullied making a lot of heat. From E10 pump fuel to E60 we picked up 60HP with only timing changes. From E60 to E85 we didn't pick up anything. Threw so much timing at it we started falling off, but never a lick of knock detection. I feel there are huge gains to be had in marine blown applications and with flex fuel it can be convenient... just throw whatever fuel in and the computer adjusts accordingly. Any advancement here?

I considered building my 598 NA engine to run on E85 with Holley EFI - but I would have had the compression up so high that I would have to run that or race fuel.
People I talked to told me unless I bought RACE E85 the engine wouldn't last due to inconsistent alcohol content.

I'm not sure of the consistency of alcohol content of E85 by you but I find that hard to believe. E85 around here ranges from 70-85 depending on the season. It is at least 75 from early spring to late fall. 10% change is not going to affect the octane.

I believe you can run a flex fuel sensor with the Holley? I run a flex fuel sensor on my ecu and it makes any needed changes.

I've head the fuel consistency problem mentioned several times by people who've looked into this change. In reality, I wouldn't let it impact my decision in any way... The alcohol to gasoline percentage is just a number, nothing you can't control or change to suit your specifications at will. The options are pretty simple and all listed above.

1) Setup the engine like any modern car with ECU and sensors that "sniff" the fuel. This design adjusts the fuel and timing tables to match the E%. The OEM's fit all fix.

2) Tune conservatively for a lower alcohol / higher gasoline levels than you plan to run. Set everything up for E70 blends lets say and there is no chance of damage running a E85. You just won't get full advantage of that extra timing edge. Could even run a spot test at the pump and top off with some gasoline to back down a true E85 to that E70 level.

3) Blend your own fuel. No issues buying 99% ethanol from larger distributors her in the states and blending some high test gasoline into it. The cheap test kit I listed above is all you need. Want a E85, E90, E95 blend every time, roll your own it's as simple as making coffee..

4) Buy VP race fuel in drums and for a few extra pennies per gallon all problems solved.

I would love to if only my tanks were larger