Octane rating

[aiki]

Thinking on the fuel prices, why is it we are set on the higher more expensive octane fuels. I have checked my info on my bike, and it is recommended fuel over 87 rating so 91 should do well. Look at this site for some interesting facts on fuel. http://www.leeric.lsu.edu/bgbb/7/ecep/trans/b/b.htm
My bikes compression rating seems perfect to use the 91 completely.
Any wise souls who know better are welcome to let me know.

[Motu]

Because there are a lot of vehicles on the road that require a higher octane fuel.These people have the right to keep these vehicles on the road,and so therefore have the right to be supplied with a fuel that allows them to run efficiently.You may think they are stupid,and that such old or modified vehicles should be banned from our roads.If so,I suggest you join the Labour Party and put the legistation in place - although I think they have it well in hand.

[Ixion]

Alfatoy is 2001, so not exactly old, warns in NO uncertain terms, in the drivers manual, in the boot, and behind the fuel filler cap that you MUST use minimum 95RON fuel ONLY.

[Motu]

Well the octane rating for that car is far too high - please surrender car and keys to your nearest police station....um,hang on,I have a faaaaar better idea.....

[aiki]

Why is it my post topics bring out the loonies who can't see the wood from the trees, often simple questions have simple answers.
The reality is likely we put the wrong octane in our tanks thinking it will perform better.

[Motu]

I don't think anyone does that,most shop on price alone.

[skidMark]

Why is it my post topics bring out the loonies who can't see the wood from the trees, often simple questions have simple answers.

now i think you are missing the point....

this is kiwibiker....

WE ARE ALL LOONIES :slap:

[Quartida]

I don't think anyone does that,most shop on price alone.

This is the problem....I persist in filling my '89 Lancer with 95 or above as it has a large sign in RED AND WHITE LETTERING that insists

"USE 96 OCTANE FUEL ONLY"

(OK, I do use 95, but that's because 96 doesn't exist any longer.)

And people laugh at me as they tell me that it actually "doesn't matter that much".

But as some caring people have explained to me, it DOES matter. And besides, I cannot ignore signs. I just can't.

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

[skidMark]

rip the sticker off and put 91 in it......

once i put BP 98 octane in my gpx among every other bike ive ever owned i have tried it in just once to see how it goes.....they advertise smooter acceleration yer it was bloodey smoother alright thats cus thier was none! it has made every single one of my bikes a gutless pile of poo (yes more than usual) when i put 98 in i put 91 in and they perform so much better

[scumdog]

This is the problem....I persist in filling my '89 Lancer with 95 or above as it has a large sign in RED AND WHITE LETTERING that insists

"USE 96 OCTANE FUEL ONLY"

(OK, I do use 95, but that's because 96 doesn't exist any longer.)

And people laugh at me as they tell me that it actually "doesn't matter that much".

But as some caring people have explained to me, it DOES matter. And besides, I cannot ignore signs. I just can't.

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

Just stand near an intersection on a hilly part of town and listen to the cars 'pinking' as the drivers lug them up the hill in too high a gear on too low an octane fuel.. I shudder to think what it's doing to piston tops etc.

I could run 91 in my 10.5 to 1 comp.ratio 429 V8 - IF I retarded the timing by about 10 degrees!! Then it would run like it was 3 litres instead of 7 - BUT use the 7 litres worth of fuel.!!!
i.e. running a fair bit of advance and expensive high octane can be more fuel eficient than sticking to cheaper fuel but less timing advance...

Go with what the 'book' says - and if you feel like playing then advance the timing and use the more expensive fuel - I know I can tell the difference in horsepower.

Modern 'puter controlled engine do the adjusting for you - only they don't advance the timing for high octane fuel so much as retard it for poor quality
(low octane) fuel.

[Quartida]

That makes me feel better.
My argument has always been - I am a typical girl. I know little or nothing about engines and fuel, except you need one to keep the other going. Therefore, I shall follow manufacturers' suggestions as they know more than I do.

I always suspected there was a good reason for using the right fuel, so I am glad that I now understand the reasoning a lot better.

Now all I need (don't worry, you don't actually HAVE to explain it to me, I'll find out from someone who has many hours of free time) is exactly HOW the octanes work and WHY it makes the engine run less/more efficiently.

Then I will have achieved "petrol harmony". And I can wiggle my tongue at the naysayers.

[skidMark]

Just stand near an intersection on a hilly part of town and listen to the cars 'pinking' as the drivers lug them up the hill in too high a gear on too low an octane fuel.. I shudder to think what it's doing to piston tops etc.

I could run 91 in my 10.5 to 1 comp.ratio 429 V8 - IF I retarded the timing by about 10 degrees!! Then it would run like it was 3 litres instead of 7 - BUT use the 7 litres worth of fuel.!!!
i.e. running a fair bit of advance and expensive high octane can be more fuel eficient than sticking to cheaper fuel but less timing advance...

Go with what the 'book' says - and if you feel like playing then advance the timing and use the more expensive fuel - I know I can tell the difference in horsepower.

Modern 'puter controlled engine do the adjusting for you - only they don't advance the timing for high octane fuel so much as retard it for poor quality
(low octane) fuel.

how much hp would one expect to gain on a 40 hp gpx 250 if one was to advance the timing and put 98 octane in her?

[BeakerRAT]

Go with what the 'book' says - and if you feel like playing then advance the timing and use the more expensive fuel - I know I can tell the difference in horsepower.

Modern 'puter controlled engine do the adjusting for you - only they don't advance the timing for high octane fuel so much as retard it for poor quality
(low octane) fuel.[/QUOTE]

I agree - and note the fuel we get here is often of poor quality. They use all manner of additives to get the octane rating to the levels quoted.

[Ixion]

That makes me feel better.
My argument has always been - I am a typical girl. I know little or nothing about engines and fuel, except you need one to keep the other going. Therefore, I shall follow manufacturers' suggestions as they know more than I do.

I always suspected there was a good reason for using the right fuel, so I am glad that I now understand the reasoning a lot better.

Now all I need (don't worry, you don't actually HAVE to explain it to me, I'll find out from someone who has many hours of free time) is exactly HOW the octanes work and WHY it makes the engine run less/more efficiently.

Then I will have achieved "petrol harmony". And I can wiggle my tongue at the naysayers.

Very wise. There is more nonsense talked about octane rating than any other topic. Your engine, and any other engine, is designed to work with a certain octane rating. Some engines will be designed for a higher rating , some for low. Stick with using the fuel which your engine was designed for.

The simple simon explanation of how octanes work.

Engines suck in air/fuel mixture, then squeeze the mixture, before the spark plug ignites it and makes it burn. It is the burning of the fuel which produces power.

Some engines are designed to squeeze the fuel mixture more than others. The amount of squeeze is called the compression ratio.

But if you squeeze too hard, the mixture may EXPLODE instead of burning. This can cause major damage to the engine.Explosions do that.

Fuel with higher octane eating is less likely to explode than lower rating.But, conversely, higher octane fuel burns slower than lower octane. Other factors being equal, the faster the fuel burns the more power you get.

So if you have an engine designed with lots of squeeze ("high compression ratio"), you need higher octane rating . Or your engine may be damaged.

But if you have an engine with less squeeze ("lower compression ratio"), and you use high octane fuel, the fuel wont burn fast enough, and the engine will have less power. So you lose on power and pay more too.

Putting high octane fuel into your low squeeze engine won't give more power. it will give less.

simple rule:
More squeeze, more octane.
High squeeze, low octane = bad.
Low squeeze high octane = bad.

How do you know which octane rating you need. Read the handbook!

Remember, that just because someone else reckons HIS engine runs fine on 91 , yours may not - they may have different compression ratios. And vice versa. Follow the manufacturers recommendation. It is just possible they know something about the engine they designed.

Of course, it's far more complicated than that.It always is, isn't it. But that's the principle of it.

[Quartida]

Ixion, sometimes I feel like you know everything.

Thanks