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Minimum octane 98?

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I'm sure this subject has likely been discussed before, but quite frankly my phone sucks and the search feature on this site isn't that great (sorry moderator). My 2004 (not 2007) crf230f has a sticker on the rear fender that says minimum octane 98. The manual for the 2007 says 86 I believe. Does my bike really need 98 octane fuel? I'm currently running 93 and it seems to be ok.

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Your bike is air cooled. So....

If you drive at lower altitude, at slow speed single track, in really hot weather, during hi load, open throttle, steep up hills and are 200lbs or more then:

IMO

You should should use 91-2-3 octane premium pump even IF it's properly jetted.

If it's completely untouched stock it will be super lean. So if you ride in above conditions I still would recommend premium pump.

If everything is opposite of above, you will be fine with 87-89 pump.

But again, IMO:

Those bikes get such great mileage,

You won't be spending much on premium pump any way, so it would be added insurance against detonation and/or Pre-ignition.

Just my 2 cents worth....

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My 2004 also has that sticker. I think its a mistake, perhaps they meant Research Octane, rather than Motor Octane or more common Pump octane rating which is a simple average of RO and MO. 97 RO is about 91 or 92, which is common premium.

I run premium and I weigh 270, so the poor little 230 is working pretty hard.

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You're supposed to match the octane rating to cylinder compression ratio. The 230F @ 9:1 compression ratio isn't a high compression motor ; thus it should be fed regular unleaded 87 oct gas only )at 0-5000ft ASL. B/C when you use a high octane fuel on a low compression motor, there's this thing called laminar flame speed that comes into the picture. It's how rapidly the flame front of a turbulent flame will propagate at a velocity in part due to the mixture's chemical properties, or in other words, how rapidly the fuel and air explodes inside the cylinder.

If you use too high of an octane for the compression ratio, the flame front travels slower, and thus you wind up losing power.

 

Another thing to keep in mind is that, as the altitude gets higher above sea level, there is less oxygen in the air/ fuel ratio. Thus, the octane rating needs to be lower for proper combustion. In other words, if you use 87 octane at sea level, then you will be using 85 octane at 10000 ft ASL. Rightly so, gas pumps at high altitude locations will only have 85-89 octane, vs. 87-93 octane at sea level.

Edited by jeddclampette

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Octane requirement is not just about static compression ratio.  I don't know about the rest of you but my CRF230 gets screaming hot in the tight trails here in NC in the summer.  I have my Trail Tech Vapor set to turn the lights on between 300 and 350 F and the red light comes on often in the tight stuff.  Hemispherical combustion chamber designs are prone to detonation.  Couple that with low air flow and more initial advance and you are asking for trouble.  With that much heat in the head I'll stick to 93 octane.

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At 10,000 to 12,000 feet elevation---where I've done most of my riding in the past 10 or so years--- I've mixed in 87 or 89 pump octane fuel (as a way to cheat on/approximate leaner jetting) on my stock-jetted/stock air filter/stock exhaust CRF230F.  Seems to work great, with no sputtering or stumbling like you would have with a too-rich fuel-to-air ratio; there's less power than at sea level, but the less oxygen/lower atmospheric pressure at those high elevations accounts for the less power there. Spark plug has always checked out as light brown color.  No detonation, either.

 

The gas pumps at Mammoth Lakes, California (avg elevation some 7,000 feet) show 87, 89, and 92 octane for sale---probably because many customers there are passing through to lower elevations as well?

Edited by BSAVictor

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