Octane differences

[FishStretcher]

You will likely find that non ethanol fuel makes more power above 5000 rpm. It does in my car (but it it lightly turbocharged). 91 non ethanol makes more power at high rpm than 93 E10. Otherwise, power is the same. This in a car with a knock sensor. I'd suspect a EFI merc I/O or a supercharged outboard would be the most similar as they have knock sensors.

But the knock sensor retards timing to make power. Not remove it. Less high rpm advance means less negative work means more power.

It appears from the data I collected that E10 burns a lot more slowly than non ethanol. With a lot more advance and LESS power above 5000 RPM.

Anyways at cruise, differences should be minimal. But rec 90 or 91 Mogas is likely ideal for outboards if I extrapolate my data.

[cdavisdb]

Since we are talking about alcohol gas, an observation:

When E10 first showed up, I kept track of my work truck milage, over and over, switching back and forth between alcohol and the cheapest non-alcohol gas. Consistently, I got more miles from the non-alcohol gas, something like 3-5 percent.

[FLexpat]

Originally Posted by cdavisdb

Since we are talking about alcohol gas, an observation:

When E10 first showed up, I kept track of my work truck milage, over and over, switching back and forth between alcohol and the cheapest non-alcohol gas. Consistently, I got more miles from the non-alcohol gas, something like 3-5 percent.

Thats about right; the heat content of alcohol is lower than gasoline and the E10 blend runs 4-5% lower than for straight gasoline.

[gofastsandman]

Originally Posted by FishStretcher

You will likely find that non ethanol fuel makes more power above 5000 rpm. It does in my car (but it it lightly turbocharged). 91 non ethanol makes more power at high rpm than 93 E10. Otherwise, power is the same. This in a car with a knock sensor. I'd suspect a EFI merc I/O or a supercharged outboard would be the most similar as they have knock sensors.

But the knock sensor retards timing to make power. Not remove it. Less high rpm advance means less negative work means more power.

It appears from the data I collected that E10 burns a lot more slowly than non ethanol. With a lot more advance and LESS power above 5000 RPM.

Anyways at cruise, differences should be minimal. But rec 90 or 91 Mogas is likely ideal for outboards if I extrapolate my data.

Alcohol injection has long been used in boosted engines as it brings down burn temps and allows more timing. Water injection does the same thing. Water and alcohol injection is common on boosted engines that are pushing the limits.

The knock sensor retahhhds timing so it stays in one piece.
Your results may differ. Or not.

[Bushwacker]

Originally Posted by 76Red18

. . . I think alcohol burns a little cooler also.

Not true. Although E-10 gas contains less energy than pure gasoline as Connor has observed, when you add ethyl alcohol (C2H2OH) to gasoline, you end up replacing some of the hydrocarbon atoms with an oxygen atom, so at the same fuel/air ratio, it will tend to burn hotter due to the extra oxygen! It also burns slower, as do higher octane fuels, so it's used as an octane booster, and as Sandy mentioned, that's why it was used with water injection on highly boosted supercharged/turbocharged engines to prevent detonation. I believe a 10% mixture is worth about +4 points in octane, but beware . . . if you get enough water in it to combine with all the ethanol and separate out, what you thought was 87 octane gas suddenly becomes 83 octane gas, enough to quickly destroy an engine via pre-ignition. (You can't hear pre-ignition on a 2-stroke motor, since there are no valves to rattle, so the first sign of it is when it blows a hole in a piston!)

On newer engines designed to run on E-10 gas, the engines are typically calibrated to run slightly richer mixtures which burn cooler, to compensate for the effects of the extra oxygen. One potential problem with running E-10 gas in an older engine that wasn't designed for it is that it won't have the larger jets for the richer mixture, so you have less margin against the very high temps cause by lean combustion. A slightly lean condition caused by a fuel line restriction or slightly plugged jet that an old motor might tolerate if running pure gas could prove fatal to the same motor running E-10 gas! So if you're running an older (early 90's or older motor) I'd try to run pure gasoline in it if at all possible!

[OilFieldMan]

Follow what the manual says. I follow the manual specs during heavy use in the summer. When I store it for the winter I fill with premium, since gasoline degrades over time.

[gofastsandman]

Originally Posted by Bushwacker

Not true. Although E-10 gas contains less energy than pure gasoline as Connor has observed, when you add ethyl alcohol (C2H2OH) to gasoline, you end up replacing some of the hydrocarbon atoms with an oxygen atom, so at the same fuel/air ratio, it will tend to burn hotter due to the extra oxygen! It also burns slower, as do higher octane fuels, so it's used as an octane booster, and as Sandy mentioned, that's why it was used with water injection on highly boosted supercharged/turbocharged engines to prevent detonation. I believe a 10% mixture is worth about +4 points in octane, but beware . . . if you get enough water in it to combine with all the ethanol and separate out, what you thought was 87 octane gas suddenly becomes 83 octane gas, enough to quickly destroy an engine via pre-ignition. (You can't hear pre-ignition on a 2-stroke motor, since there are no valves to rattle, so the first sign of it is when it blows a hole in a piston!)

On newer engines designed to run on E-10 gas, the engines are typically calibrated to run slightly richer mixtures which burn cooler, to compensate for the effects of the extra oxygen. One potential problem with running E-10 gas in an older engine that wasn't designed for it is that it won't have the larger jets for the richer mixture, so you have less margin against the very high temps cause by lean combustion. A slightly lean condition caused by a fuel line restriction or slightly plugged jet that an old motor might tolerate if running pure gas could prove fatal to the same motor running E-10 gas! So if you're running an older (early 90's or older motor) I'd try to run pure gasoline in it if at all possible!

Alcohol is a potent solvent. As such, I avoid it like the plague.
Pretty much everything in my 96 rude fuel system is plastic and rubber of some sort.
The old style metal trip deuce carbs were so much more refined than the plastic minlons.

OMC probably saved 500 per motah with the minlons. The older omc`s sound like carbd yammis. Sewing machines.