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100 Octane Gas Road Legal


Guest South_paw

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Guest South_paw

Anyone every try this fuel? 100 oct, unleaded, no ethanol & legal for road use. It's expensive, but I don't drive my car enough for the price to be a major factor. I cant get non racing ethanol free gas anywhere around here. The way I understand it is, ethanol increases the octane and is factored into the octane rating. My concern with the ethanol is that it evaporates too quickly and because of my limited use of the car, I'm left with a lower octane gas than what my car is happy running on. So my thinking is I could kill two birds with one stone using this fuel.... no ethanol and get 100 octane fuel. Which is what my 56 Caddy was designed to run on. What say you? School me on this if I am off base:cool:

IMG_1275.jpg

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There are issues with ethanol (mostly overblown as far as passenger car use is concerned), but they all related to incompatibility with 2 things: long term storage (w/ consequent atmospheric water absorption) and incompatible aged fuel system component materials. Ethanol does no evaporate any faster than the light-end hydrocarbons that make um the vast majority of "pure" gasoline. It does lower the vapor pressure of the overall mixture, though, which can aggravate fuel percolation issues*.

I'm not sure what the compression ratio is for a 1956 Cadillac, but I think it is unlikely to be a good fit with octane levels this high. Octane ratings are strictly a measure of the speed of detonation (i.e. the "flame front") of a given fuel, not the inherent power in that detonation. That is why slower burning ethanol raises octane but has a lower heat/power content. Using a fuel with too much octane can result in incomplete combustion, and resultant carbon buildup.

It may be beneficial to use this fuel for long term storage (although you can get that benefit from a ethanol fuel additive like Stabil's). For every day use unless you're experiencing serious percolation issues, or have very old rubber/cork/etc. fuel system components that haven't been updated in decades, there is likely little if any benefit for the expense of using racing fuel.

Now if you're running a 12:1 compression W30 or other drag racing engine....

==========================

*It's important to note that "pure" gasoline isn't what it used to be 20 years ago either, containing some lighter components than in the past which do not matter to modern fuel injection systems. Percolation is aggravated by ethanol, but by no means caused by it.

Edited by Dave@Moon
added last paragraph w/ * (see edit history)
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Guest South_paw

Thank Dave. I have a better understanding now. The compression ratio of the Cadillac 365 is 9:75 to 1, so it isn't too high. Cadillac does call for 97 octane as the fuel requirement at sea level (I'm at sea level), also according to Cadillac, the hotter it gets the higher the requirement gets. So in the summer 97 + is required. The best I can do with pump gas around here is 93. Just trying to find a way to get to the required octane. Everything in my car is brand new and compatible with alcohol. I don't have an issue with ethanol per se.

Here's a pic from the 1956 Cadillac Serviceman issue. This is where I'm getting my requirements from. Thanks again.

IMG_1276.jpg

Edited by South_paw (see edit history)
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This gets back into the "pump" octane and "Research" octane issues. What's posted on the pump is "Research" octane + "Motor" octane, with the sum being averaged to yield the "Posted Pump Octane" number. From my decades-ago figuring, 95 posted pump octane was equivalent to 100 Research Octane. This DERIVED octane number did not exist prior to about 1972. Prior to that, all octane numbers quoted were "Research" octane. 92-93 "Super Unleaded" would equate to 97 Research octane, which was considered to be "Premium" in the later 1950s and such, with "Premium" later being closer to 99-100 as technology and the need for such higher-rated fuels existed.

What makes the gasoline "road legal" is that the "excise tax" which goes into the highway building fund is included in the price of the fuel. Fuel at marinas and airports will NOT have that included, as those vehicles aren't "road-driven", typically. So, "road legal" is a tax issue rather than "the type of fuel" issue. This might vary from state to state, or even region to region in some cases, but it's a "road use tax" in the price that makes it "road legal".

A NEAT graphic on octane requirement. The thinner air "up there" means a less-full cylinder charge in the cylinder. With less cylinder pressure (as in a lower actual compression ratio), less octane needed to keep clatter minimized. In some cases, you can advance the base timing a few degrees to get a little more power. There might also be a carburetor jetting listing in the carb section for the higher altitudes, also.

Octane level will not make any real difference unless the fuel being used has an octane level lower than what the engine really needs (for the driving style of the driver and tuning of the engine). It's the OTHER characteristics of "the blend" which makes things act like we like them to . . . quick starts, hot or cold . . . good vaporization for higher efficiency . . . good "shelf life" . . . etc.

Enjoy!

NTX5467

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What makes the gasoline "road legal" is that the "excise tax" which goes into the highway building fund is included in the price of the fuel. Fuel at marinas and airports will NOT have that included, as those vehicles aren't "road-driven", typically. So, "road legal" is a tax issue rather than "the type of fuel" issue. This might vary from state to state, or even region to region in some cases, but it's a "road use tax" in the price that makes it "road legal".

"Road legal" also would indicate that the fuel is unleaded as well as taxed. Leaded fuels are still legal only for off-road use, and many racing fuels are still leaded.

This material is most likely Sunoco 260 GT racing fuel ( http://www.racegas.com/fuel/17 ).

Edited by Dave@Moon
typo (see edit history)
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Guest South_paw
I know you said money isn't an issue, but I would at least make someone buy me dinner before they charged me $9.75 a gallon for gas. :P

Anything for my ride... LOL. In two years, I have only done 120 miles. So I'm only looking at roughly $100 bucks per year to burn this fuel.

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Southpaw - take a second look at the post of Willis (NTX) about the octane rating systems.

Your car will NOT perform as well on the current 100 octane fuel as it would on probably 91~92 octane fuel. Running a fuel with too high an octane for the engine will result in lost power as well as reduced fuel economy due to unburned fuel.

And I need a set of the tires used on the car in the graphic!!!;)

Jon.

Edited by carbking (see edit history)
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