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Thread: Fuel Octane rating for /5

  1. #1
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    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
    Administrator 20774's Avatar
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    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 grade...you'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 Administrator ---> 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
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    what he said

    http://www.mbzponton.org/valueadded/...cal/octane.htm

    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
    My prized possessions. 74 R90/6 Mine! (also know by bride as the Black Hole). 09 R1200 GS. My wife, 1953 model who has survived aplastic anemia and a bone marrow transplant. My most prized possession is my relationship with Jesus!

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