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Thread: Fuel Octane rating for /5

  1. #1

    Fuel Octane rating for /5

    Recently bought a 1973 R75/5 toaster in great shape. Also purchased some original tools and the owners manual for the /5 series. On page 14 the grade of fuel is specified as 99 octane (ROZ) for the R60 and R75. Is this a typo or was there some other octane rating back in the day. I had a R60/5 back in 1972 and don't remember having run any thing other than regular gas in it for 60K miles.
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  2. #2
    Liaison 20774's Avatar
    Join Date
    Sep 2005
    San Antonio, TX
    The difference is the use of ROZ versus RON, Europe versus the US. Typically what we see here is (RON+MON)/2 which is research octane number plus motor octane number divided by two. The US version of octane is probably 10 points lower that those in Europe. For your /5, you shouldn't need the supreme level but maybe the middle grade. You might even be able to use the lowest're bike will let you know if the octane is too low by giving you some pinging when you roll on the throttle.

    Do some googling about fuel octane and you'll see what it's all about.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
    P Monk
    Join Date
    May 2005
    Orange, Texas

    what he said

    basically right. ROZ is RON in German. Research octane is pretty useless to predict knock since it is run on an engine without much of a load. It really shows an engine at idle. Motor octane is run on an engine with higher compression. It simulates your engine under a load. The ASTM spec for unleaded regular is 82.

    After retirement, I went back to work for a while and one of the projects was a new gasoline blender. It didn't rely on octane engines but on gas spectrometers to predict octane. I am really getting to be old school I guess.

    My experience is that my airhead needs premium gas. But I live at sea level and in a hot environment. How much carbon have you built up on your piston crown and head. That raises your octane requirement. If I lived at 5000 feet or so I could probably run midgrade with no problem.
    P. Monk
    74 R90/6 (the Black Hole) Harvey couldn't kill it. . 09 R1200 GS, drowned in Harvey replaced by 2011 R1200RT. Wife, 1953 model survived aplastic anemia and a bone marrow transplant.

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