There have been several discussions here on the subject. The short answer is that 87 is well above the minimum required for these low compression engines and they will perform better with the lower octane fuel. The lower octane fuel will generally start easier in cold weather and produce more power. Even the high compression high altitude Super Hurricane and the OHC Tornados will run fine on 87. My little hurricane 4 drinks 87 octane ethanol blend almost exclusively.What fuel you guys using? I’m figuring 93 makes the most sense since these motors were built to run on fully leaded fuel at least a higher octane would be best?
Octane was rated differenty when these vehicles were made and cannot be compared to the numbers on the pump today.What fuel you guys using? I’m figuring 93 makes the most sense since these motors were built to run on fully leaded fuel at least a higher octane would be best?
Thanks stakebed!Greg, to answer your question completely requires a bit of history and a lesson in octane numbers. Back when our Willys were new, I believe octane was calculated and advertised via the Research Octane Number, RON. Now, at least here on the Left Coast, octane is expressed using the AKI or R+M/2 method. So today's fuel rated at 91, has a higher octane capability than 91 fuel from the early fifties and earlier.
Plus, our compression ratios are absurdly low compared to domestic engines produced even as early as the late fifties. The exception that I'm unfamiliar with is the Tornado.
So Greg, what does that mean regarding your question? It means that typically today's 87 R+M/2 or AKI octane is fine for our engines. If you increase the effective compression ratio or the cylinder filling ability, then your octane needs rise. For a better understanding of octane read this:
Research Octane Number (RON)
The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane. The Compression ratio is varied during the test in order to challenge the fuel's antiknocking tendency as an increase in the compression ratio will increase the chances of knocking.
Motor Octane Number (MON)
Another type of octane rating, called Motor Octane Number (MON), is determined at 900 rpm engine speed instead of the 600 rpm for RON. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern pump gasoline will be about 8 to 12 octane lower than the RON, but there is no direct link between RON and MON. Pump gasoline specifications typically require both a minimum RON and a minimum MON.
Anti-Knock Index (AKI) or (R+M)/2
In most countries in Europe (also in Australia, Pakistan and New Zealand) the "headline" octane rating shown on the pump is the RON, but in Canada, the United States, Brazil, and some other countries, the headline number is the simple mean or average of the RON and the MON, called the Anti-Knock Index (AKI), and often written on pumps as (R+M)/2.
Difference between RON, MON, and AKI
Because of the 8 to 12 octane number difference between RON and MON noted above, the AKI shown in Canada and the United States is 4 to 6 octane numbers lower than elsewhere in the world for the same fuel. This difference between RON and MON is known as the fuel's sensitivity, and is not typically published for those countries that use the Anti-Knock Index labelling system.
See the table in the following section for a comparison.
No question, but higher octane fuel doesn't add more power, just burns slower. Perhaps if you could advance the timing more, but I doubt it.I agree with Flinthillsben, like oil, fuel goes on top of the list of most overthought things in a Willys truck/wagon/jeep.
I bet it comes down to the fact that we are all " optimizers" at heart. If the 226 only has 115 hp we want all 115 hp or 1 or 2 more. It's why I bought an electronic ignition, hot coil, Weber Carb.... lOL.. none of it needed, all of it wanted.
Premium doesn't actually burn slower, it just resists self ignition better when pertaining to compression ratio or bad combustion chamber design. It does not increase horsepower unless you have pre ignition or detonation issues and you have covered them up by retarding timing. If your engine is tuned to factory spec and you have no detonation or spark knock issues, premium, (91 octane), will not increase you power and is a waste of money. Use a top tier gas and you'll have no issues. My 91 Harley Davidson owners manual actually said not to run 91 as it would cause deposits. I don't know if that was pertaining to the MTBE or whatever that oxygenator agent was back then that they banned.I mainly run 91 no ethanol because it is the non ethanol fuel most widely available in my area. So I advanced my timing to suit the slower burn. I run the leaded fuel periodically because the lead lubricates and does more than the typical valve seat padding answer. In a car with an exhaust heat butterfly it lubricates the action and keeps the butterfly free(er) to move, exhaust valve guides/stems get some love, cylinder walls too. 100LL avgas is rated for long term storage so I usually fill up with that before the long salty winter months.
I don't see fuel as a means to performance - to the point earlier its just speed of burn, I see it as something fun to mess with in my Tinker toy Willys Wagon family vacation vehicle. Plus My wife can't complain about this gas or that gas when I fill up vs a new overdrive, or 7.3 cylinder head(recently on ebay.) I mean who here hasn't gotten the 3rd degree from the significant other for that part you just had to have....