Hey brother I wondered the same thing when I got the bike, 91 works fine for me. The RC is fairly high compression but as with all octane it depends on your particular situation. Throw a gallon or so of 91 in it and ride it around, if it doesn't ping or run poorly then you will be fine (by the way there is a natural flat spot around 5k rpm and a little on/off throttle factory so don't stress over that). Some climates/altitudes may need the 92, but I have ridden in temps from 42degree F up to 112, and from 800ft to 3200 ft over the last 1.5 years and never had a problem. Technacly you will make more power with the lowest octane that resist pinging anyway (trust me, no need to get the octane fight going again). By the way check out www.rc51.org and www.rc51.com for more stuff on this bike.

 

I use it without any apparent problems. Whatever "premium" is when I roll through a gas station. What can you do, but take the highest pump octane available at the particular station? I just assume they don't want you using 87...

 

I run the mid-grade stuff; works as well as the 91

 

Does the sticker say if it's a RON octane number, MON octane number, or the average of the two (R+M/2 octane number)?

 

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JoeFriday said:
Does the sticker say if it's a RON octane number, MON octane number, or the average of the two (R+M/2 octane number)?

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That would be the PON (Pump Octane Number) :smile:

My sticker on the tank says use 95 Octane (european spec) but we only get 93 Octane up here. I have had no problems 380000 Km's later.

 

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The RC is fairly high compression

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relative to what...? it's got the lowest compression of anything rolling. and that assumes optimal valve timing with the intakes being effectively closed at BDC (which they never are). it's C/R dare i say is lower than bikes being produced 10 years ago. :shocked: because the engine was meant to be "built" the ratio is almost "car-like" from the factory. and certainly not radical ignition timing as stock. it's always been a honda trait. not that 92 is all that high anyway, but not sure why they spec out such an octane number...? maybe for the detergent additives...? maybe it applied at one point to the early euro SP-1 models and they just slapped the same sticker on all of 'em and nobody ever thought about it...? who knows...? i'd try some different grades and see what works best, but my guess is you'll be hard pressed to tell the differences without some serious tuning adjustments to go along with it. and with us no longer enjoying the "spoiled" gas prices of yore (not that that ever mattered in tax heavy california)... ya know what grade wins right...? :crazy: as nemo says, the 91 works fine, don't even waste your time looking for 92-94. in better news, sort some hi-C pistons from kyle along with some tuning and she'll blow a "99-whatever" into the weeds let alone your 3/4 duck. :grin:

 

yea you know I was not sure the exact compression, I was making the assumption based on the minimum octane rating. I am so used to running methanol (in cars not bikes) that compression of 14:1+ is of no concern.

 

The RC needs higher octane levels, but not race gas high levels because it has a more radical ignition curve that allows the RC to make the horspower numbers that it does. It has nothing much to do with compression. Without getting too in depth on something I know little about, I just know that the RC 51 has an ignition timing curve that demands a higher octane level. Unlike other sportbikes that like 87 but everyone puts premium in, the RC actually needs 92 or 91 octane to make its best power numbers. You can run 87 octane in the RC or even 100 octane, but the dyno numbers will show some horsepower loss. Think of the bike as a Mercedes as opposed to a Ford Taurus. Both are cars and both use gas. One was designed to make peak power and run its best with premium gas and the other with normal 87 octane. It is the same for the RC. It is just how they were engineered and I am one who doesn't like to ignore the time and energy some engineer put into something that I own, I just go with what it recommends.