87 or 93 octane?

59 Willys Duxbury MA

Bigger Hammer
Aug 16, 2020
52
Duxbury
First Name
Greg
Willys Model
Wagon
Willys Year:
1959
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?
 

6T1L226

Sharpest Tool
All-Star
Feb 10, 2017
436
California USA
First Name
Joe
Willys Model
Pickup
Willys Year:
1953
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?
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.
 

Big Dog Frank

Well Oiled
Feb 12, 2016
1,791
North Lawrence,Ohio
First Name
Frank
Willys Model
Pickup
Willys Year:
1959
87 here also with ethanol. I can't afford the top shelf stuff in a truck that goes about 11 miles on a gallon. Now I also have a Volkswagen engine that is just under 10 to 1 compression that dosent like 87 at all so it gets top shelf 93 and if I am feeling frisky on the weekend I may add some 110 to the mix. On a cool damp night it's like opening a can of wheel standing whoop ass.
 

vintagetrk

Precision Fit
All-Star
Apr 28, 2018
692
NW Wyoming
First Name
nathan
Willys Model
Pickup
Willys Year:
1958
I always go with 91 for the simple reason its the only selection without ethanol in it. If I had a choice I think straight 85 would be my pick. It would be a little cheaper for sure! I live at 5,000 ft. so 91 is overkill. If its really 91. Found this little snippet below.

Past tests of vehicles show that their octane number requirements decrease with altitude. As a result, gasoline marketers sell lower-octane-number (ON) gasoline in the mountain states and other high-altitude areas.
 

cwdtmmrs

Well Oiled
Jul 19, 2012
2,828
First Name
Tim
Willys Model
Wagon
Willys Year:
1952
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.
 

airportops

Bigger Hammer
All-Star
Jan 1, 2019
66
Conroe, Texas
First Name
Terry
Willys Model
Wagon
Willys Year:
1960
Living and working on an airport I thought I was being smart taking advantage of the self service 100Low Lead avgas pump about 100 yards from my shop for my L134 2A. Then a pilot gave me an old bulletin from the 70's that said if you are going to run 100LL you had better always get it up to operating temp and when you land give it full power before you shut it down or you will ruin the valves. Boy was that the truth - I ended up having to pull the head and soak the valves for three days and still had to hammer two of them out of the block. So don't chase the high octane leaded gas. I've been running regular 87 ethanol pump gas through one of Scoutpilots carbs ever since that valve job and several thousand miles later - no problems.
 

Stakebed

Well Oiled
All-Star
Mar 4, 2020
2,717
Northern California
First Name
Joseph
Willys Model
Pickup
Willys Year:
1957
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)[edit]
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)[edit]
Another type of octane rating, called Motor Octane Number (MON), is determined at 900 rpm engine speed instead of the 600 rpm for RON.[1] 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.[citation needed]

Anti-Knock Index (AKI) or (R+M)/2[edit]
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[edit]
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,[5] 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.
 

59 Willys Duxbury MA

Bigger Hammer
Aug 16, 2020
52
Duxbury
First Name
Greg
Willys Model
Wagon
Willys Year:
1959
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)[edit]
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)[edit]
Another type of octane rating, called Motor Octane Number (MON), is determined at 900 rpm engine speed instead of the 600 rpm for RON.[1] 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.[citation needed]

Anti-Knock Index (AKI) or (R+M)/2[edit]
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[edit]
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,[5] 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.
Thanks stakebed!
 

Flinthillsben

Precision Fit
All-Star
Oct 26, 2016
940
Gardner, Kansas
First Name
Ben
Willys Model
Wagon
Willys Year:
1957
I timed my engine a little earlier and run a random when available/needed; 91 ethanol free, 87 ethanol free, 110 leaded(mixed 1-2 gallons with the rest 87 EFree) or 100Low Lead mixed with whatever. Never had any lead issues, sometimes add MMO to lubricate the carb and scavenge some post burn lead. Never had an issue in a variety of vehicles, engines with this formula.

Of course on trips its always best available which sometimes means ethanol blend.

Like engine oil - to each their own.
 

vintagetrk

Precision Fit
All-Star
Apr 28, 2018
692
NW Wyoming
First Name
nathan
Willys Model
Pickup
Willys Year:
1958
I believe we are safe to conclude that... most everything is safe to use. Ethanol you might want to make sure the rubber in the vehicle can take it ( hoses, gaskets, diaphragms.) from what I have been told.

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.
 

cwdtmmrs

Well Oiled
Jul 19, 2012
2,828
First Name
Tim
Willys Model
Wagon
Willys Year:
1952
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.
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.
 

Flinthillsben

Precision Fit
All-Star
Oct 26, 2016
940
Gardner, Kansas
First Name
Ben
Willys Model
Wagon
Willys Year:
1957
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....
 

airportops

Bigger Hammer
All-Star
Jan 1, 2019
66
Conroe, Texas
First Name
Terry
Willys Model
Wagon
Willys Year:
1960
Two thumbs up Ben, my lead problem with 100LL was my many very short trips using the 2A for and airport vehicle, but it does work great for storing things like our mowers for when the grass doesn't grow here in Texas (basically no winters for the Willys). And RATS, I didn't see the 7.3 cylinder head :mad:.
 

Jeffp

Knuckle Buster
Jun 1, 2020
2
Michigan
First Name
Jeff
Willys Model
Wagon
Willys Year:
1950
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....
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.
 
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