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Gas: 87 (regular) or 91 (premium)?
I tried both and on 91 bike runs much better, feels like it gives more power. Is this real feeling or something imaginary?
 

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on high compression engines you get more power and better fuel economy from higher octane, i dunno how it would affect our bikes. i'm just thankful to have something that doesn't take premium for once
 

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Filling up with premium doesn't bother me too much, $9 a fillup vs. $8.25 *shrug*. Dealership put premium in it to begin with, I've just been using premium since.
 

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I've been using the 91+... not for the octane, but because that's the only choice available in my area which is non-oxygenated.
 

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Filling up with premium doesn't bother me too much, $9 a fillup vs. $8.25 *shrug*. Dealership put premium in it to begin with, I've just been using premium since.
I know it's not much money but it really is pointless. It's not going to have any impact on how your bike performs, gas mileage or anything else.

The Low-Down on High Octane Gasoline
 

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Higher octane shouldn't really change performance since that's not it's function.
The higher the octane, the less chance of the fuel/air mix detonating in a hot engine before the spark plug sets it off thus creating "knock". As the mix compresses it builds heat and under enough compression can heat up enough to ignite itself. This is why racing engines running high compression must use 100+ octane fuel.

With a 10:1 compression ratio, 87 regular has plenty enough octane for the 250.

But.. If you feel better going with the higher stuff then by all means go for it. It certainly can't harm anything and if if gives you peace of mind it is money well spent.
 

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I've always assumed that all sport bikes took premium octane because they're high performance machines.
Right. And the CBR250 is not a high performance machine. Honda just took great pains to make it look like one (and I do think they made the right choices in that department).
 

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Recommended fuel is PON (pump octane number) 86 or higher, page 28 of owners manual. Looks like regular is OK according to Honda.

regards
Badger
 

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On a side note:
Running high octane fuel in a low compression engine can actually make you lose power because it is so much harder to ignite the mix inside the combustion chamber.

DoubleRGirl, most supersport engines run high compression such as 12:1 which is why they require premium gas. The higher octane really is needed so as to not have the mix ignite prematurely.
The 250 runs a low 10:1 compression.
 

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I thought the compression ratio is 10.7 to 1, but that is from my memory which just ain't what it used to be. 20 years ago you had trouble running compression ratios above 9 to 1 but as combustion chamber design fuel injection and timing control have all improved the ratio has gone higher.

The new Mazda sky-active engine group is running compression ratios at 14 to 1 on regular fuel. They accomplish this with many advances including high amounts of exhaust gas recirculation, but the most significant improvement is to actually inject the fuel directly into the combustion chamber at pressure close to 25-30,000 PSI (200 atmospheres). These injections are separated into 5 separate mini injections with no pre ignition since the fuel quantity is not sufficient for pre ignition with most of the fuel delivered after combustion has actually initiated.

I filled with 87 E10 regular and can not tell any difference in mileage and performance, which makes sense if you are building a bike for the world market that is supposed to be efficient, why burden it with higher octane requirements (read expensive fuel).

regards
Badger
 

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I actually got worse gas mileage out of tank full of 91 octane than I did with a tank full 87...coincidence or not...I have been filling up with 87 octane ever since...other than that..I can tell absolutely no difference between the 2 except for a higher price tag for the 91 when i pay.
 

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Myth: Higher octane in a given motor will give more performance.

Truth: Engines are tuned from the factory to run a particular octane. Octane is simply (without going into the mechanics of it) the rate at which the fuel will burn and its resistance to detonation as pressure builds. An engine tuned for higher octane will have its ignition timing advanced to take advantage of the more stable fuel, and also have higher mechanical compression ratios built in. Cam timing is usually set to allow higher cylinder pressure, which in turn requires stronger rods, pistons, etc... Now, an engine tuned for 87 Octane will run worse generally with higher octane fuel. The reason is the fuel will not completely combust because of the slower burn time, and allow maximum cylinder pressure as a result, equalling less horsepower. Fuel is typically ignited BEFORE the piston reaches TDC and maximum cylinder pressure is ideally reached just as the piston begins the downstroke. If you use fuel that burns slower than the engine is tuned for, maximum cylinder pressure will not happen until well after the piston is moving down the cylinder (ATDC), meaning you will not get the maximum "bang" for your buck so to speak.

Equally, by using a lower octane fuel than a motor is tuned for, the fuel could detonate or burn to quickly, causing cylinder pressure to max out before TDC, resulting in tremendous strain on the engine and possibly shattering it (this is why many people who use nitrous and dont tune for it end up with a pile of parts, but I digress...).

In short, unless you know what you are doing and retune for higher octane, use what the manufacturer recommends (87 for the CBR250R). Sorry for the long post.
 

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We rate our fuel differently
Malaysia uses RON method (Research Octane Number)
USA uses an Anti-Knock Index (R+M)/2 that is RON+MON/2
RON= Research Octane Number MON=Motor Octane Number

In most countries, including Australia and all of those in Europe, the "headline" octane rating shown on the pump is the RON, but in Canada, the United States and some other countries, like Brazil, the headline number is the average of the RON and the MON, called the Anti-Knock Index (AKI, and often written on pumps as (R+M)/2). It may also sometimes be called the Pump Octane Number (PON).

Because of these differences, the octane rating shown in the United States is 4 to 5 points lower than the rating shown elsewhere in the world for the same fuel. Your 95 would equal 90-91 octane in the USA.
 
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