100 Octane Gas Question

[jvelde]

I have found a source for aviation gas that I think is 96-100 octane (with lead but no ethanol) to put in my '39 Buick. My question is, before I do this will I need to adjust the carb to accomodate the change from regular (86 octane) pump gas to 96-100 octane? If just rich/lean adjustment is required and not changing jets, I can handle it, but what should I expect and should I do it?

Thanks,

[PONTIAC1953]

I have found a source for aviation gas that I think is 96-100 octane (with lead but no ethanol) to put in my '39 Buick. My question is, before I do this will I need to adjust the carb to accomodate the change from regular (86 octane) pump gas to 96-100 octane? If just rich/lean adjustment is required and not changing jets, I can handle it, but what should I expect and should I do it?

Thanks,

i think your 1939 buick engine in it's stock confiquration will never need anything other than just regular gasoline, are you wanting the aviation gasoline because it has no ethanol ?, i don't know where you are, but you can search online for gasoline brands in each state that still allows the sale of non ethanol gasoline.

[jvelde]

I am in North Texas, and the nearest "real gas" I have found from prior web searches is about 60 miles away, so just under a half tank round trip. I am interested in the leaded gas with no ethanol due to the less damaging effects on an older engine - just don't want to create worse new problems by using higher octane gasoline.

[CarNucopia]

My understanding of octane is it's a measure of how stable the gas is when compressed. The higher the number, the less volatile under pressure. The benefit of high octane is it lets you have a higher compression ratio and therefor more power. I would think running 100 in a '39 would be a bad idea. I had a Miata that wouldn't start on cold days when I put 93 octane in it. But, I have to admit, I have no idea what your compression ratio is or what the standard gas of the day was back in 1939.

I can't find pure gas in my area either, so I understand the appeal and feel your pain.

[Thriller]

I am less concerned about octane and more about ethanol.

Up here, premium fuel, which is the highest rated octane available at the pump, doesn't have ethanol. Low and mid grades have ethanol (by law). It costs more. I don't recall the premium octane rating, but I've had no issues with my '41. The only collectible Buick that willingly sees ethanol is the Reatta, but it is quite modern and sees more use generally. If I'm travelling (like to a National), I don't worry too much about it, although I will purchase ethanol-free gasoline if it is convenient.

Another thing to consider is simply low long a tank sits. If you are using the car and burning the fuel, then ethanol is less of a concern, at least in its water-absorbing properties.

[Marty Roth]

As I understand it, the higher octane fuel will be MORE subject to vapor lock when facing heat and altitude conditions. It should not harm your engine nearly as much as it will decimate your checkbook, but that is better than the problems which ethanol would cause. Where some get into trouble with higher octane gas, is that they "hot-rod" by excessive spark advance, since the high octane minimizes or eliminates pre-ignition (spark-rap), and if you go too far, you could burn a hole in the top of a piston.

Running correct "Tune-Up Specs" with higher than minimum octane, you should be OK.

[FLYER15015]

John,

If you are talking about "Avgas" from your local airport, I ran this by some of my EAA friends, and they don't think running Avgas 100% is a good idea, as it does not contain many of the additives contained in motor fuel. Sure it's a higher octain, but that can be obtained by adding "octane booster", and did you ever notice that those products contain mostly Naptha, Toluole and MEK.

As an alternate idea, you could probably add a gallon or two to a full tank and get away with it, but why.

Then there is the question of "road taxes" if your secret source info gets into the wrong hands, such as some "eco-nut".

Just my $ .02.

Mike in Colorado

EAA # 863720

Edited April 21, 2013 by FLYER15015 (see edit history)

[michaelod]

Back in my youth when I was clearly insane, I once owned a Chevy shortbed pickup with an LS-7 454 engine that I purchased new as a crate motor from Chevrolet and transplanted into the truck. I believe it had a solid lifter cam, as well as a 12:1 compression ratio and I ran nothing but avgas in it. Actually the engine would ping on anything normally available at the pump. At that time I am also sure the octane rating was >100. I used to pull up to a local airport near my home that accommodated small aircraft and fill the truck on a regular basis. The gas was green in color as I recall rather than the standard orange hue normally seen. I never developed any problems from the use of that gas, at least that I am aware of.

Thanks,

Edited April 19, 2013 by michaelod (see edit history)

[jvelde]

Thanks to all for the comments - don't seem to have a consensus one way or the other here. Think I will hold off filling up till we have more views.

[nickelroadster]

You should be aware that using av gas in your motor vehicle is against the law. You do not want to have someone turn you in to the EPA.

[ply33]

Thanks to all for the comments - don't seem to have a consensus one way or the other here. Think I will hold off filling up till we have more views.

May have to wait a long, long time if you are going to wait for a consensus view.

[danhar1960]

I wouldn't do it. If I recall correctly, the octane rating back in the '40s was only in the low 80s so 100 is just way overkill and costly. I'd just go with the E-free premium from the bowser and save yourself all the other agro.

Danny

[5219]

The owners manual for my 1940 LaSalle says that fuel should be no less than 72 octane. I suppose that that was the standard fuel available around 1939 or 1940.

[jvelde]

Between the legality issue (which I never considered) and the cost, think I will forego the avgas idea.

Thanks for the advice and thoughts.

[Barney Eaton]

I have been told that todays Premium gas contains less ethanol than the 87 octaine "regular" How could we find out if this is true?

I have been filling my little used cars with Premium ('39 Buick and '91 Reatta) hoping it was true. Neither car "needs" Premium but neither is driver more than a couple hundred miles a year so the cost is not a big issue.

I just helped a friend with his Corvair......3 of the four carbs were gummed with something that we are blaming on the ethanol gas. We had rebuilt the carbs about 2 years ago. These ethanol stories are passed around, it would be great to get some real FACTS.

Depending on who you listen to, I have been told that ethanol either costs more or less than gas, so if the refinery adds ethanol are they actually increasing or decreasing the cost to produce a gallon of gas? In Texas, our pumps say "up to 10% ethanol" but I am unable to get a actual figure.

[carbking]

OK - will have a go at this, will probably get some disagreement, so you will still probably not have a consensus.

(1) As previously stated in this thread, the use of avgas in an automobile engine used on our highways violates a number of laws, because various government entities did not receive road taxes on the fuel. There is probably a consensus on this point.

(2) While I tend to blame a lot on ethanol (and it deserves a lot of blame;)), gasoline which was allowed to evaporate caused gum in carburetors prior to the use of ethanol. This issue does seem to be worsening.

(3) You stated that your owners manual stated that the octane rating for your fuel should be no less than 72 octane. This statement, as written, is misleading. Why, because a number of different rating systems have been used. PROBABLY, your manual is referring to RON (research octane number) which is higher for the same fuel than MON (motor octane number). Neither system has been used in the USA for several years. The system now used is the AKI (anti knock index) which is defined as ( R + M ) / 2. GUESSING, the MON for 72 octane is probably around 68; so again guessing, the modern AKI necessary for your engine would be 70 ( 72 + 68 ) / 2.

(4) Octane is a family of hydrocarbons, but octane ratings measure, among other things, the resistance of a fuel to "knock". The larger the octane rating number, the slower burning of the fuel, and the greater resistance to knock. Generally, engine makers specify higher compression and more spark advance when using higher octane fuels. Low compression engines with very little spark advance will not burn all of the fuel, thereby (sometimes significantly), reducing the engine efficiency.

(5) Energy content of fuel. Once (when there was real gasoline), there was 117,600 BTU's per gallon of gasoline. This figure was independent of the octane rating, as octane rating and energy are different entities. According to the independant Machinist's Handbook, ethanol contains 67,000 BTU's per gallon (the government and the farmers claim a slightly higher number, I personally trust the Machinist's Handbook more than the government). Thus mixing ethanol (regardless of which figure one uses for ethanol) with gasoline is going to reduce the energy content of the resultant fuel. Also, the AKI of ethanol is approximately 116. Very fuel engines, other than racing engines, have the necessary compression or spark advance to burn all of the ethanol. thus the effective energy content will be even lower.

I would suggest that for your 1939/1940 Buick, the best fuel to run would be the lowest grade fuel which you can purchase at a name brand station. Higher octane fuel is going to be more costly at the pump and probably perform WORSE due to your engine characteristics.

Just my 25 cents ( 2 cents adjusted for inflation).

Jon.

Edited April 22, 2013 by carbking (see edit history)

[danhar1960]

I would suggest that for your 1939/1940 Buick, the best fuel to run would be the lowest grade fuel which you can purchase at a name brand station. Higher octane fuel is going to be more costly at the pump and probably perform WORSE due to your engine characteristics.

Just my 25 cents ( 2 cents adjusted for inflation).

Jon.

Just for clarifaction Jon, is this "lowest grade fuel" with or without ethanol ??

Danny

[carbking]

Just for clarifaction Jon, is this "lowest grade fuel" with or without ethanol ??

Danny

Since ethanol is much higher in octane than gasoline, generally the higher the octane rating, the more ethanol will be included.

If you can avoid the ethanol fuel do so, but don't use 100 octane avgas to eliminate the ethanol.

Jon.

[carbking]

And in the FWIW category, Wikipedia has a really good, easy to understand article on the meaning of octane ratings. I would highly recommend it to all. Just use the search engine of your choice and search for octane ratings. The more one understands the problems, the more one may deal successfully with the problems.

Jon.

[Guest outlaw car man]

I agree with Carbking. As someone who has been fighting the use of vodka laced gas, and used to make alcohol as a profession, AKA beer. It evaporates at a lower temp, which in turn leaves gum when sitting, like in a hot garage. Also eats rubber products and dries things up. It does clean but also evaporates, we all know this, and that's a good thing-I use regular gas in my 1933 Buick 90, BUT have also been using Blue Stabil as an additive. I also , at least try, to run the car up every week to get the gas flowing thru the system. AND, it's been working. That's my only answer to the issue, which has been a big pain in the keester !OCM

[60FlatTop]

Here is a good place to check:Ethanol-free gas stations in the U.S. and Canada

Bernie

[FLYER15015]

Hi Sandy,

It's a clear sunny day in B.V. How's yours ? Up to your knees in snow yet ?

I too use the Blue Stabil in our baby. Just changed the oil and filter, and gave her a grease job. She's been sleeping all winter with a full tank of gas. Going to wake her up this Saturday with a 40 mile cruize down to Salida for lunch.

Can't believe it's only 4 weeks to the car show @ the ABBY in Cannon City (5/18/13) and Merchants day show in Florence on the 19th.

Mike in Colorado

[Guest outlaw car man]

Snowing like hell in the high plains, 2.5 maybe. We got 23.2 inches last week, all melted in the Colorado sun, then this again. You guys and your " new " Buicks, running all over the Rocky Mountains. Haaaa . Hope you made a lot of money this year selling beaver pelts up there, pay for lunch in Salida. Spent the winter there in 07, with my mule. Sandy