At the risk of sounding thick... What octane is best?

[Damantis]

Am a learner on my 1st bike, a 95 honda cbr 250rr. Should I run it on regular or 96, or that bp 98?

[Monsterbishi]

95 is just fine.

[McJim]

To answer this question in the future a good guide is to find out what the compression of your engine is.

High compression then higher octane is better low compression lower octane is better.

high octane in a low compression engine will take longer to ignite. 91 has a lower flash point than 95 at a given pressure for example.

[Damantis]

To answer this question in the future a good guide is to find out what the compression of your engine is.

High compression then higher octane is better low compression lower octane is better.

high octane in a low compression engine will take longer to ignite. 91 has a lower flash point than 95 at a given pressure for example.

Compression is 11.5-1 How do I know if that is high or low tho? Have been googling my bike and found some good info etc mut no fuel recommendations. I have put some caltex premium in it and seems to run nice but wont be riding much till through the week. Will note the kms and see how many I get til it hits the reserve, then run it till almost empty, fill it with 91 and compare I guess

[McJim]

Pretty much anything over 11-1 is high comp.

Mine is about 9.5-1 so I use cheap fuel..nice.

[Damantis]

Sweet. thanx. lovin this site, alot of knoledge round here.

[McJim]

Sweet. thanx. lovin this site, alot of knoledge round here.

Yeah, Especially the difference between 2 stroke and 4 stroke eh?

2 stroke - fires every time the piston reaches the top of its stroke
4 stroke - fires every second time the piston reaches the top of its stroke

1 Cylinder - has one Cylinder and can be 2 or 4 stroke
2 Cylinder - has two cylinders and can be 2 or 4 stroke
3 Cylinder - has three cylinders and can be 2 or 4 stroke
4 cylinder - has four cylinders and can be 2 or 4 stroke.

There is some more knowledge wot I have given you for free and for nuffin'

Enjoy Kiwibiker.

[fizbin]

Pretty much anything over 11-1 is high comp.

Mine is about 9.5-1 so I use cheap fuel..nice.

so my suzuki has 12.2 to 1 compression that would mean that 95 would be the better fuel right?
i put a tank of 91 in it today what is the difference?

[musicman]

My bike engine apparently has 12:1 compression, I usually run it on 91 (the previous owner did too). What differences do 91/95/98 make?

[discotex]

From memory the 250 IL4's are spec'd for 91 octane or higher.

That said it largely depends on how your carb has been jetted. 95 is a safe bet to avoid pre-detonation problems on a high compression motor but anything higher (98 etc) would be a waste on a 250.

[discotex]

My bike engine apparently has 12:1 compression, I usually run it on 91 (the previous owner did too). What differences do 91/95/98 make?

http://en.wikipedia.org/wiki/Octane_rating will tell you everything you ever wanted to know.

We use the RON scale in NZ.

Basically high octane lets manufacturers make engines with higher compression ratios (turbos, litrebikes, etc) without the fuel igniting under compression (rather than waiting for the spark).

If you run your engine with too low octane it will knock. Problem is you probably won't be able to hear it on a bike. If you run too high octane you just waste money.

[musicman]

If you run your engine with too low octane it will knock. Problem is you probably won't be able to hear it on a bike. If you run too high octane you just waste money.

Then... how do we know which octane fuel is 'just right' for our bikes? Owner's manual? Or trial and error?

[discotex]

Then... how do we know which octane fuel is 'just right' for our bikes? Owner's manual? Or trial and error?

Owners manual in the first instance. Trial and error and work out which gives better mileage is probably the next best option.

If in doubt run 95 and you'll be fine.

[breakaway]

What's this I hear about 'tuning' a bike to a certain type of fuel? If compression ratio is what determines what octane is best, what has tuning to to do with it?

[R1madness]

Run it on 91. Save yourself a few cents per litre.
Think of it like this,
Low octane = low flame point but fast flame spread. Good for std compression and high revs.
Mid octane = higher flame point, slower spread. Harder to ignite. Medium revs and higher compression motors like this stuff
High octane = difficult to burn, slow spread, best in high comp low rev motors (like V twins)

However, if your bike has been spacificly tuned by playing with the exhaust and or fueling then stick to whatever runs best in it.

Remember our fuel is NOT petrol in the true sence of the word, it is a combination of cheap base materials and added hydrocarbons. Find a fuel your bike likes and stick to it.