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Honda CBR250RA 2012
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What octane gas should I use for my 2012 CBR250?
Definately 98 octane. I've tried a combination of 98 and e85 at a ratio of 6 to 1.( 6 parts 98 and 1 part e85). I noticed improved throttle response and at partial throttle the revs build to a higher amount. But I used to race (go karts) and I'm more sensitive to changes than the average rider.( some claim it makes no difference). Never run straight e85 because of issues with corrosion. And you'd need programmable fuel injection or it would be way too lean. Have fun experimenting. You can also try a mixture of different octanes. Ie; - 91,95, 98. 91 gives you more bottom end but no top end. With the reverse being the case for 98. I wish they still made 100 octane. Eg Shell Optimax. It was a great fuel with good bottom end, top end and fuel economy. Ride to live. Regards Wazza.
 

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Note that U.S. octane rating is different than what you find in other countries.

U.S. = PON = (RON+MON)/2. ; Pump Octane Number = average of research/lab octane and motor octane ratings
RoW = RON ; research octane number

The conversions tend to look like this:

RON 98 = US PON 93
RON 95 = US PON 91

Stoich AFRs for various mixes

petrol = 14.7:1
E10 = 14.04:1
E15 = 13.9:1
E85 = 9.75:1

When blended, you'd used weighted-average to arrive at final stoich AFR of your mix. For example a 6:1 mix of RON 98 + E85 would be:

(6*14.7 + 1*9.75)/7 = 13.99:1 AFR , this is pretty much same mix as E15

With O2-sensor feedback, no worries about running too lean or rich, it will auto-correct to lambda = 1. Under WOT open-loop operation, ECU is mapped too rich anyway at ~11:1 or so. Leaning out mixtures tend to increase power, max-power on NA engines are around 13.5:1 (remember that '60s hot-rod motto).

Absolutely ZERO, NO, NADA, ZIP major manufacturer will ever map ECU for maximum-power, it's too risky without safety margin for random cases such as super-hot day or clogged injectors, failing fuel-pump or getting bad batch of petrol in wilderness. That's where aftermarket "tunes" comes in with leaning out mixtures under WOT to increase max-power. But carries some risk.

Certain combination of engine parameters (compression, redline, cam-specs, intake/exhaust, cylinder-diameter, bore/stroke ratios, etc.) will work better with certain mixes than others. What works best for one engine will not be best for another. In end, only valid comparison of differences between fuels is instrumented testing such as 1/4-mile times, radar-tested top-speeds, lap-times around racetrack under STP or dyno-charts. Otherwise, it's all in your head.
 

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I've tried a few tanks of Premium gas over the years. The first time I did I seemed to notice the slightest possible increase in power, but ever since that first time any time I use octane over the recommended 87 I get an even more noticeable hesitation and rough idle. I'm done experimenting.
 

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Yeah, there have been reports of higher-octane fuels being more difficult to ignite. They typically go with higher-compression/higher-boost engines which requires stronger ignition for denser mixtures. Ethanol has flame-front propagation-speed about 25% slower than gasoline, and it cools combustion. So effects may be caused by more than just octane rating. All these differences would also lower power-output. So increased compression/boost needs to be used with ethanol-based fuels to make most of them.

Now, true higher-power fuels such as nitromethane carries their own on-board oxygen supply and burns about 2x as fast as gasoline. Also generates 2-3x as much power, but extremely difficult to control. Can get out of control and explode your engine into pile of rubble.:)
 
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