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Why Hi Octane?

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I ran 91 for several tanks in the gf's 451, then ran 87 for several tanks. If there was a difference in "power", it wasn't noticeable. Mileage was slightly worse with 87, about 5.7 vs 5.5 on 91. 

I never noticed any adverse effects switching fuels like stumbling or knock or anything like that. Realistically, any car equipped with a knock sensor will be able to detect the onset of detonation and retard ignition timing long before you could "hear" it.


One thing to consider is that fuels with ethanol blended into them already have a built in "gas line antifreeze" and "injector cleaner", as these additive use an ethanol analog, often naphthalene, methanol, or methyl hydrate. I have seen people experience fuel filter or injector clogging when an ethanol blend fuel is used in a car that has spent it's life running on non-ethanol fuels. The non-ethanol fuel often allows buildup of varnish/goop especially if the car is driven infrequently or never gets totally hot. When you add an ethanol fuel or a fuel injector cleaner it will sometime cause these deposits to slough off and end up clogging small orifi. Of course when that happens people are quick to tell you how they put ethanol fuel in and that's what caused the issue, which, is not *really* the truth. I've often managed to "cure" poor-running cars with the use of high concentrations of methyl hydrate and some good old fashioned long-haul drives keeping engine load low.


Now, older cars, small engines that are carbureted, or engines that frequently sit for extended periods of time, I think can be quite sensitive to damage from ethanol fuels. Owing to ethanol's propensity to adhere to water, if sitting for a long period of time, will pull water out of the air and then pool in the bottom of the fuel tank or carb bowl and wreak havoc from there. Especially where you have brass components involved like in carbs.

Interestingly, our daily driver 451 has a factory-looking sticker on the fuel door stating "Use only 91 RON fuel". I say interesting because I haven't noticed the same sticker on other 451s I've come across, not that I was looking very hard. And as we know 91 RON is roughly equivalent to 87 (R+M)/2. I'm wondering if the previous owner might have replaced the fuel door with a euro door from eBay or something if his was damaged. The owner's manual however is very clear about using only premium 91 (R+M)/2 fuel.

Anyway... long post just to say I don't buy into the whole "ethanol is the devil" thing. In fact quite the opposite, I think ethanol fuels are great for applications where the fuel isn't allowed to sit for months at a time. But, like most everything in life, you have to understand that "to ethanol or not to ethanol" isn't a question with a one-size-fits-all answer.

As for me, I run ethanol fuels the majority of the time in my 451s with no adverse effects seen as of yet, and I buy ethanol free for winter storage of my yard equipment and "toys".

It would be interesting to log ignition advance curves in the 451 for different conditions and fuels to find out if there's a set of conditions where the car starts pulling ignition timing to correct for detonation. Like, would you get full timing advance in winter running 87 but not in summer, owing to a difference in intake air temp, or if you were to stay away from a certain load/rpm part of the rev range, or do you see the difference between fuels under any condition. Would make for an interesting comparison. For my efforts, the difference in mileage between 87 and 91 was seen in the middle of the hot summer. I should re-run the comparison in winter to see if there's still a difference. Or would the difference simply be owing the a slightly different BTU value between an ethanol and non-ethanol fuel? So many variables...

Probably not worth the effort to find out. lol

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On 2/6/2018 at 5:47 PM, Huronlad said:

The 451 fuel door sticker calls for 95 RON fuel.


Finally got around to taking a pic of the fuel door. I was wrong about it saying use only 91 RON, but it certainly says 91 RON as a minimum, which would be equivalent to 87 AKI that we have posted at our Canadian pumps.


Edited by booneylander

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