octane question

[larky]

I found a link to vintagesnow.com and of course proceeded to the john deere section. here is the link:

http://www.vintagesnow.com/John_Deere.html

Now I am confused. The FAQ on JDsleds.com says to use the highest octane fuel in my 76' cyclone. has that recommendation been changed? It said on vintagesnow.com that 1975-1984, 88 octane or better.

Thanks,
Matt

[harleysportster]

Matt,
I don't know where he found his info that is posted, I would stick with the original recommendation of "high octane" for the 76 cyclone. The combustion chamber/porting was changed in 77 for the a lower octane gas.

[WinnipegStPaul9]

Octane ratings today are not the same as the octane ratings in the 70's. Can anyone remember when the change took place and if I'm not mistaken, ratings today are higher. It may have had something to do with removing lead from the gas in the 70's.

[jdsledhead]

Yes Don is correct. The ratings were changed, but I also do not know the year. I believe it is safe to run 87 regular pump gas through just about any regular production Deere. I do however run 93 in my 82 Liquifire, along with Arcticcat 50:1 injection oil, although not neccesary.

[JDGuy]

There are two methods of measuring octane, one is called the Research Method (rm) and the other is called the Motor Method (mm). Both use a variable compression ratio single cylinder laboratory engine for the tests. One method gives a bit higher octane number than the other due to different test conditions. I don?t remember which was higher or lower. There are other methods, Aviation Method for AV gas and the Supercharged Method, neither apply to the pump gas we buy. This stuff I am pretty sure of.

Now I going far out on a limb here........ I think that the lower number of the two, Reseach vs. Motor, was used as the reported octane at the pump back in the all lead days. At the time of the switch to no-lead fuels, the reported octane at the pump became an average of the two, (rm+mm)/2. I think that I remember that change produced a small difference in the at the pump rating, somewhat higher number due to averaging in the higher test method, the method not used to report octane in the all lead days. Do any of you old timers (like me) remember seeing (rm+mm)/2 posted on the pumps at the change over to no-lead? It was posted only a few years. Maybe it was only a Michigan thing, as the Michigan Dept. of Ag sort of police the pumps here.

I hope I have not lead you too far astray. Maybe Joe (GM fuel cell engineer) can set the record straight for us.

[WinnipegStPaul9]

Good information Guy. Thanks. DA

[webman]

The octain ratings came from here:
http://www.freewebs.com/thesledzone/troubleshooting.htm

If it should be changed, then I will change it.

[harleysportster]

Regardless if the octane standards have changed from the past, JD had recommended a higher octane than standard low pump gas at the time, for the 76 cyclone, liquifire and liquidator. I would at least use the middle grade available today, not the standard regular.