Octane rating

**Motu** · 22nd June 2006, 18:15

It's not even compression ratio but combustion chamber design - my old XC Coon 250ci straight 6 had 9:1 compression,but a horendous bathtub combustion chamber with 2 huge valves.When we went unleaded it would rattle even on premium,and I had to use octane boosters to drive the thing,I was rapt when 98 came out because then I could run without octane boosters.But a modern engine on 9:1 with a pent roof chamber and 4 valves can happily run on 91.

**aiki** · 22nd June 2006, 18:30

Yeah, very clever loonies pity they have such trouble with forming intelligible sentences, I haven't the energy to crack their coded gems.
So please speaka da english if you want people to learn something, save your wit for your bar stool.

**aiki** · 22nd June 2006, 18:39

I would also like to add my thanks

to those who came up with such usefull information be they clever clog loonies

or not. I can certainly feel confident that my bike should perform just as well with 91 though Wgtn Motorcycles told me i should use 95. Maybe they have shares with the oil companies, who knows

**Titanium** · 22nd June 2006, 18:43

Originally Posted by 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.

Octane is not all about performance...... if you think it is the only factor .... yu are wrong.

Not loonies pal..... just people with a different opinion than yours.

**Titanium** · 22nd June 2006, 18:45

Originally Posted by aiki

Yeah, very clever loonies pity they have such trouble with forming intelligible sentences, I haven't the energy to crack their coded gems.
So please speaka da english if you want people to learn something, save your wit for your bar stool.

Got to stop labeling everyone who does not agree with you a loonie....... I see an ignore list addition......

**Titanium** · 22nd June 2006, 18:49

Originally Posted by FlyingDutchMan

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.

Wrong, higher revs require a slower, cooler burning fuel......... and of course the timing curve to complete the equation .....

It is an Octane, timing, compression ratio issue, then throw in port height and width for a 2 smoker....... oh yeah also plug temp rating once you start getting deeper in to it.

It is a common misconcetption that higher octane equal hotter faster burn.....

Just had a few years building, running 300 + horse power super stock jet skis......

The other issue is that you may not achieve the manufactures specified performace figures if you use fuel other than what is specified by the said manufacturer.

Cheers

**aiki** · 22nd June 2006, 18:53

I don't label people as loonies because they disagree with my opinion as I have no opinion just a question or 2, which i enjoy getting answered by people who might know the answers, which maybe is the reason for this forum in the first place.

**Madmax** · 22nd June 2006, 19:01

115 is fine fuck that other shit though

**aiki** · 22nd June 2006, 19:04

what the hell does that mean madmanmax

**Titanium** · 22nd June 2006, 19:07

115 Octane ...... possibly......

**aiki** · 22nd June 2006, 19:08

Don't get me wrong Titanium I love all bikers

I just can't understand half of what they say.

**Slingshot** · 22nd June 2006, 20:37

Originally Posted by Titanium

The other issue is that you may not achieve the manufactures specified performace figures if you use fuel other than what is specified by the said manufacturer.

HA HA....Achieve the manufacture's specifications....you gotta be kidding. Even following the manufacture's specs to the letter and in a perfect control environment, you'll never achieve manufacture's specifications...cause marketers make them up!

Originally Posted by TwoSeven

Has anyone figured out what octane does yet ?

Nope, but I guessing it does it eight times.