Going to higher octane increased the power today?

So when i first got my pig i was running 91 octane because i thought it would be better than 87. But then i got to thinking with a 8.3 compression ratio it would probally make more power on 87. I tried the lower octane and sure enough it DID make more power. I have been running 87 ever since. As stated in another thread the temperature dropped recently and my bike lost a little power. Today i checked my tank and it was about half way up with 87 octane. I had a jug of 91 octane sitting around for my street bike. I topped the xr's tank with the 91 and shook the bike to mix the 2 different octanes togeather. Took the bike out and the lost power due to the colder weather was back as strong as ever. I dont get it??? Can someone tell me what happened???

Well colder weather should make MORE horsepower unless your lean. Colder equals denser air equals more oxygen to the motor. I don't know that you should be able to "feel" a differance between 87 and an 87/91 mix. Not saying that it is in your head but....actually I think it might be.

Well colder weather should make MORE horsepower unless your lean. Colder equals denser air equals more oxygen to the motor. I don't know that you should be able to "feel" a differance between 87 and an 87/91 mix. Not saying that it is in your head but....actually I think it might be.

Thats what i meant. My pig is jetted perfect for summer temperature. It has gotten colder the last few days causing it too run leaner. The bike was down a little on power until i mixed 87/91, then its making more power. Its not a placebo effect, it is working better than on 87 alone.

Could the 87 have alcohol in it and the 91 not? The only way I can see it getting more power out of the mix is if there is a fuel quality change. Either way I'd jet up a bit if you are actually feeling a power difference with what I assume is a rather minor outside temp change.

Could the 87 have alcohol in it and the 91 not? The only way I can see it getting more power out of the mix is if there is a fuel quality change. Either way I'd jet up a bit if you are actually feeling a power difference with what I assume is a rather minor outside temp change.

The 91 is ethanol free. At least they claim it is.

I've been round and round the octane rodeo with with my CRF-X. It runs fine on pump gas, but ultimately I decided to keep paying a premium for 93 octane race fuel mainly because it doesn't build up quite as much crap in the carb if the bike sits for a couple of weeks

More octane for me also makes a bit less power because it burns slower I guess, but i'll take the tradeoff for the more reliable fuel --- even at the pump, when you are squirting in the 91, it may be diluted with enough 87 left in the gas station's fuel line to change the octane reading for a small application like a motorcycle gas tank or a 5 gallon jug

without reading everything, my bandit 1200 get out more power from 98+ octane than the 95 ordinary.
Have not tested it on my xr600 yet though! But i will probably do it sooner than later. :ride:

If its a racing specific fuel you will often get better power simply due to it being of better quality than the average gas station stuff.

For the original poster, I'd throw a wide band afr gauge on it and see what you have. Either way, I'd prob up the jetting a bit if your sotp dyno is actually accurate.

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