Fuel Octane

[charles lendman]

Silly question..what octane gas is best for a 51 JD ..G ..I've heard that the "new" 87 octane is so junky that it may damage the tractor under load...it's probably 20% ethenol by now ...anyway what's your thoughts?? Charles

 

[garytomaszewski]

Charles, Ethanol is limited to 10%, unless CLEARLY marked. And Ethanol will make it pull better, use E85 and nitro boost in our pullers. G s were NEVER high compression even the gas only were only 5.5 to 1, all fuels were 4.25 to 1. Don't know your area but here E10 (89octane) is $0.09 cheaper than 87 unleaded and E85 (105 octane) is $0.50 cheaper. Mix a little , open the carb jets 1/2 to 3/4 turns and use the higher octane. Octane is figured different than when the G was made so 87 now was probably around 90-92 then. One of the first tractors that even mentioned octane was the "high compression" Oliver 70 which REQUIRED at least 70 octane fuel.

 

[Bob Harvey]

Ya but- back in the day gas had our friend lead in it to offset pre-ignition (or create it , I can't remember which). Let the Pros pipe up !

 

[Roy Crane]

Octane rating is a simple numeric scale to indicate the ability of a fuel to resist firing from the heat of it's own compression. Unless you have a high compression engine you don't need high octane rated fuel.

Octane doesn't increase energy, although high compression can. Lead was only one way to boost the octane rating. Today's fuels have other additives to control octane rating and hopefully are less harmful than lead.

 

[wilamayb]

No, the octane rating is exactly the same now as it ever has been. It is derived from a relationship comparison between "Iso-octane" and pure "octane".

 

[gtx1967jewison]

GET A MANUAL! then READ your owners manual. it says " In all communities where these low-octane fuels are available, they are generally used in john deere tractors because these tractors will burn them successfully without any detrimental effect to the working parts of the tractor and at a saving in fuel costs" !!!! the G specifically. also- the 2cyl. design was at least partly chosen as a design because of the desire to burn low-octane fuels successfully. the G was an all-fuel tractor- ALL of them- & will run on anything u can get that will burn. even "kerosene & some grades of diesel" as stated in the manual. this should be left to experienced operators however as it requires carb tweaking FULL engine temp & ignition timing adjustment most likely, as yours has probably been advanced for better gasoline operation. they dont MAKE a low enough octane gas of any blend today that will even come close to causing trouble. ethanol increases octane. high octane used where not required actually results in LESS power. this is because high compression ratios ( cylinder presure @ ignition) are needed to take advantage of it. high octane gas has a higher resistance to ignition & in most cases burns slower as well, not what u want on a hand-start engine. these are FACTS. get it filled up with 100 octane race gas on the belt dyno, then again with 87 octane. u will measure a difference. u have very low cylinder pressure.

 

[gtx1967jewison]

go to a fuel website such as VP racing fuels etc.

 

[Mike Aylward]

Charles, unless your G has aluminum pistons with a flat head you will be just fine running 87 octane gas. Your tractor will run a little better with the 89 with ethanol. Unless you have a flat head on your tractor it's unlikely your compression ratio is much above 6.5 to 1 so about any gasoline will work fine. Octane is tested the same way it always has been but is now averaged between the two methods used. Mike

 

[garytomaszewski]

NO, NO, Octane ratings are now the research octane number plus the motor octane number divided by 2. Wiki will give you a good explaination of how octane is measured. Old time measure (leaded) was rated only as research octane.

 

[ET]

In 1950 regular pump gas was about 70 octane. Check out the fuel specs. on nebraska tests from that time frame.

 

[garytomaszewski]

ET, that would be the Research octane #, the motor octane # was 60-65 by the new method (that Wilamayb doesn't understand) a 70 octane then = 60-65+70/2=65-67.5 octane now, the lowest octane # I've seen posted on modern pumps has been 85. Check my previous post about Oliver 70, in 1937 Oliver REQUIRED 70 octane for the "high compression" high reving new 6 cylinder. They were one of the first to recommend the use of high octane fuel only, as most tractors of the time were low compression dual fuel.

 

[dixie deere]

gee whiz

 

[ET]

Yea I read about the oliver 70 being named for the 70 octane fuel it used. So if I understand right the 70 octane fuel back then equals about 67.5 octane now? Either way my point was todays pump gas is higher octane than what was available back when those tractors were built.

 

[buickanddeere]

It's "new math". The octane paper numbers are higher but the actual gasoline octane values are lower.
Weasel marketing 101.

 

[Tom L. Pollack]

I see one response mentions Research and Motor octane numbers. There is a BIG difference in each of these numbers are arrived at through totally different testing methods. The bottom line is you want a fuel with a higher MOTOR octane number rather than a higher RESEARCH number. You can ask your fuel supplier for more detail on this information and then hope its accurate. Ethanol does tend to increase the RESEARCH number more than the MOTOR number.