Octane rating

[inlinefour]

When I brought my new bike i was specifically told by the dealer to only put 91 into it. I was told that any fuel with a higher octane rating would be detrimental to the bikes well being. Considering I still want to have the bike when Im retired, I listen.

[ZeroIndex]

So I shop according to what is "best" for my car.

who cares what's best for your car? sell it.. you've got a bike.. that's all the transport you need..

[grandpa_dave]

Doesn't the higher octane rating mean the fuel burns SLOWER and because it burns slower it is PUSHING on the piston (during the power stroke) for longer thus producing more power.
But yeah, the fuel exploding is bad. It should burn in a controlled front from the spark plug through the cylinder, PUSHING the piston down rather than exploding and SHOVING it down, this is when some of the little (sometimes important) bit inside your engine can get bent.
If said engine is tuned to run on 91 and you chuck 98 in it for instance the fuel will still be burning after the power stroke and leave all sorts of nasty deposits on its way out of the engine. However if you switch back to 91 these should burn off again without causing any problems, although prolonged running on the wrong fuel will eventually (and we could be talking 1000's of k's) cause problems or excessive wear and tear.
Avgas has an octane rating over 100 (110 I think from memory) and still has lead in it, so if your engine is tuned to run it you will get SIGNIFICANT power gains from running it, but if your engine is tuned to run 91 you will have all sorts of problems. (Lead in petrol is a whole other, quite interesting, story-Check the "dog and lemon guide" for cars to see just how the petrol companies have everyones best interests at heart)

[aiki]

I'd like to know what the USA gas octanes are as my handbook says to use 87 octane. Now is that like 4 below our 91 or does the US use different gradings like when you compare US and UK shoe sizes.

[FlyingDutchMan]

Doesn't the higher octane rating mean the fuel burns SLOWER and because it burns slower it is PUSHING on the piston (during the power stroke) for longer thus producing more power.
But yeah, the fuel exploding is bad. It should burn in a controlled front from the spark plug through the cylinder, PUSHING the piston down rather than exploding and SHOVING it down, this is when some of the little (sometimes important) bit inside your engine can get bent.
If said engine is tuned to run on 91 and you chuck 98 in it for instance the fuel will still be burning after the power stroke and leave all sorts of nasty deposits on its way out of the engine. However if you switch back to 91 these should burn off again without causing any problems, although prolonged running on the wrong fuel will eventually (and we could be talking 1000's of k's) cause problems or excessive wear and tear.
Avgas has an octane rating over 100 (110 I think from memory) and still has lead in it, so if your engine is tuned to run it you will get SIGNIFICANT power gains from running it, but if your engine is tuned to run 91 you will have all sorts of problems. (Lead in petrol is a whole other, quite interesting, story-Check the "dog and lemon guide" for cars to see just how the petrol companies have everyones best interests at heart)

As long as the gases don't escape past the rings or valves, the pressure will remain in the piston, pushing it down. At high revs, you'll need a faster burning fuel.

Petrol has almost the same calorific value per litre regardless of octane rating. AFAIK higher octanes have slightly lower calorific values. Methanol has about 1/2 the calorific value of petrol, even though it has a much higher octane rating. As long as the stochiometric ratio is kept (12.7 parts air to 1 part petrol by mass) the maximum power output of an engine is deterimined by the amount of air that goes into it (more air = more power). This applies to internal combustion engines, jet engines, ram jets, and good old oxycetelyne torch. If you don't put more air in, you can't get more power.

On the other hand as mentioned earlier, high compression ratios or turbo'ed engines, the use of higher octane fuels is required to stop the petrol from exploding.

[Wolf]

Well, according to the specs, I'm supposed to use low octane fuel in my bike and that has been borne out by others who ride the same model - nothing but grief using high octane.

I noted that some of my old bikes ran like a haunted shithouse if I put super in them and performed so much better on regular - thanks to Ixion's "Octane for Dummies" post, I now know why.

As 91 is significantly cheaper than 95/98, I'm quite happy that my bike is supposed to run on lower octane.

I'm a bit concerned as a bloke in the States was saying his bike had issues running at 92 Octane - their "Premium" (compared with their "Regular" at 87).

Does this mean our modern 91 and 95/98 octane fuel is worse for our vehicles than the old "Regular" and "Super" fuels we had back in the leaded petrol days (which, I recall, both had lower octane than our modern counterparts)?

[Motu]

RON and MON,the octane twins.

[Skunk]

I'd like to know what the USA gas octanes are as my handbook says to use 87 octane. Now is that like 4 below our 91 or does the US use different gradings like when you compare US and UK shoe sizes.

Yep, octane ratings in the US are different to here. As Motu says MON and RON. Google it.

[Wolf]

Yep, octane ratings in the US are different to here. As Motu says MON and RON. Google it.

Thanks. Did google it and found out that the US octane is PON - Pump Octane Number - the average of the RON and MON ratings whereas ours would seem to be RON, same as Europe and Australia.

87 octane fuel, the "normal" gasoline in the US and Canada, would be 91 in Europe.

I also found a table that informs me that 95RON is 91PON, 96RON is 92PON (no wonder that American's bike was running like shit on "92 octane" and runs better on 87) and our 98RON is the equivalent of 94PON in the USA.

[Motu]

Oh,so it's the octane triplets now,I might of known.Huey Dewy and Louie.

[pritch]

Why is it my post topics bring out the loonies

LOL That's a couple of fairly senior (and knowledgable) "loonies" you have there.

[TwoSeven]

Has anyone figured out what octane does yet ?

I would have thought reading the wikipedia on petrol would have been a good start

[Wolf]

Oh,so it's the octane triplets now,I might of known.Huey Dewy and Louie.

Yep.

I should have realised that "the Yanks" would use a different fuel rating than everyone else, after all, they use gallons rather than litres (and even then they're American gallons rather than real gallons), they've eschewed the entire metric system, use fahrenheit rather than celsius, their light switches are upside down and they hold their knives and forks in the wrong hands - why would they use the same octane rating system?

(joke/piss-take)

[Motu]

Has anyone figured out what octane does yet ?

In this day and age it means absolutly nothing - the whole octane thing was developed back when motors were sidevalves if they were lucky,and running about 5:1 compression.These days it's not about balancing octane and iso heptane,it's a whole new cocktail brew.And it's not even about compression ratio,but combustion chamber design and cam profiles.

[SARGE]

the only time you need to run super high octane (race gas) or even 98 is if your compression is higher than standard or you are at hi altitude.. anything else and you are pouring good $$ down the shitter for Ego's sake

i have a high comp big bore that sounds like a caribbean steel drum on anything less than 98 ( 14.5/1 compression)

most bikes run nice on 91