What fuel?

[davebullet]

It's hard to find concensus on this but I doubt that many stock 250's would run better on 95/98 than they do on 91. Higher octane fuels do not automatically give an engine more power, they actually just burn longer and later in the compression cycle which may not suit many smaller capacity engines.

Also higher octane fuels tend to include more additives and cleaners which most of the time you are better off without and especially if your engine isn't completely combusting the fuel due to it not being tuned for it.

Partial reference:
http://homepages.slingshot.co.nz/~sh...ml#Question_18

I thought the higher the octane rating, the more resistant the fuel to pre-ignition - nothing to do with burning longer. Therefore it would make sense that engines running high compression ratios are likely to need higher octane fuel - to minimise the chance of compression induced ignition.

In other words the burn rate is the same for both fuels.

[Spuds1234]

Generally the higher the compression rating, the higher the octane rating you would use.

Have a gander at this link for more info.

http://www.faqs.org/faqs/autos/gasol...section-1.html

[SMOKEU]

There are different octane ratings as well. I've heard that American 91 octane (for example) isn't the same as NZ 91 octane, as there are different octane scales. Correct me if I'm wrong.

[neels]

There are different octane ratings as well. I've heard that American 91 octane (for example) isn't the same as NZ 91 octane, as there are different octane scales. Correct me if I'm wrong.

You are right, but most specify the RON (Research Octane Number) rating which is what is used at the local servo.

[slofox]

Basically, yes, higher compression ratio needs higher octane.

BUT:

Compression ratio on its own isn't the whole story on detonation. The degree of turbulence in the combustion chamber is one other factor - which is why "squish" heads were invented once upon a time. So gas flow patterns, head design and combustion chamber shape all come into it as well...I once had a pretty cool techie book on intake and exhaust design...wonder what happened to that? I bet some fucker borrowed it and "forgot" to return it...

[ola_bitchola1]

I allways use 95 or higher in my 2 smoker not sure why just allways ran my cars on 95 or better my race car loves 98 so much it can consume a whole tank in 350ks

[AllanB]

Maybe phone Casbolts and or Hamptons - they should be able to look it up for you.

Be 91 or 95 - F-all specifies 98.

If the 91 preformed well and there was no audible pinking I'd say all good.

[SMOKEU]

I allways use 95 or higher in my 2 smoker not sure why just allways ran my cars on 95 or better my race car loves 98 so much it can consume a whole tank in 350ks

How big is the tank?

[Phreak]

I've tried 91, 95 and 98 in my CBR, doesn't like 98 much, and gets better mileage on 95 than 91... So I fill up with 95 every time now.

[ola_bitchola1]

How big is the tank?

45L its only 1.6L motor

[SMOKEU]

45L its only 1.6L motor

And you think that's bad, my 2L car drinks 40L of fuel in 250km without even going over half throttle.

[JMemonic]

Out of interest did you know formula one race rules require that the cars run on maximum RON 91 and it has to be pump gas with no additional additives. Your bog standard bikes are most likely only needing 91 if you are really keen on demonstration any improvement gained on you bike from altering the fuels book some dyno time, run the bike on 91, 95 and 98 making no alterations and see how much benefit or gain you get from the higher octane.

Then you will be able save the money you spent on the dyno time by using the correct fuel and not paying up to what 15 cents a litre extra for you fuel, might take a while unless of course you want actually get out there and ride.

There is plenty of good info on the net about this subject written by some very bright minds.

[imdying]

Check your manual out to see what your compression ratio is and then base your fuel purchases off that.

Easy.

Shouldn't you check the valve timing too in that case?

[Juzz976]

Older bikes with worn needles/jets may require higher RON fuel as they'll be running slightly richer than a newer bike. CV carbs are more prone to wear as the needles tend to vibrate.

My FZR runs better on 95/98 but the major thing is on cold starts it will idle better.
Different fuels have different octane ratings and additives, the RON figure is only is resistance to pre detonation not the ration of octane.

[Techno]

91 in the Bandit, it doesn't like anything else.

Really, what year is it?

I haven't tried 91 as I was told to use 95 or 98. Seems to run ok on those.