Octane Ratings explained

[roland2003]

Hi Guys, here is some easy to read info on octane ratings for all.
OK , Octane is a fuels resistance to 'knock' .The higher the number the greater the resistance. Knock is very undesirable as it is the point where the fuel is no longer burning
in one controlled direction (moving from the plug) but self igniting causing two flame fronts to collide.
Octane can be measured in 2 ways ,both using very slow speed single cylinder engines. MON tests at WOT, whereas RON tests at half throttle. Because of this ,logic
suggests that a good MON figure is more important to us than the RON figure,as you
dont race on half throttle!
In the UK and Europe our fuel at the pumps is rated as a RON figure. As a general rule the RON figure is about 8 higher than the MON . Therefore 98 RON 'Optimax' is around 90 MON.
In the US they use 'AKI' which is the average of the RON and the MON . Therefore what we
call 98 they call 94.
AFAIK the highest octane unleaded race fuel possible is circa 106 RON / 98 MON.
With leaded fuels the RON can go to almost 130 ! . If you run leaded you will murder the
cat and the lambda sensors tooso dont do it.
So why bother with high octane if the timing can be retarded to prevent knock?
OK, the 3 variables which can be increased if we utilize more octane are;- compression,
boost pressure,ignition advance,or any combination of these. Assuming everything else is ok,all 3 will increase power.
Im sure there's loads more I've missed but my brain is now a total void.
Regards Roland Gt Tuning

[rasp]

Interesting!...thanks...

[Wobert]

RON = Research Octane Number

MON = Motor Octane Number

Yes?

[LordNikon]

I've got a drum of Cool Blue 106Ron fuel in my garage. Might stick it in and see how she goes .... or blows

[RallyMINI]

http://www.geocities.com/TimesSquare...6/octane1.html

This guy explains the actual engine used to test octane, and has links to several historical sites related to Octane engines... pretty neat.

Thanks for bring this up, I learned something new today!

RMout

[roland2003]

Wobert Thats correct
LordNikon Yes give it a go,and let me know what you think. TBH Ive never tried race fuel
in the Mini.I might get some but is expensive ,its ok for a Kart or M'Cycle which uses alot less fuel.
Regards Roland G T Tuning.

[pocketrocketowner]

Using higher octane in an engine that is not tuned for it is a waste of money. It will essentially do nothing. The beauty of higher octane fuel is that you can use a higher compression ratio and or advance the timing significantly both of which will make the engine generate more power, quicker.

[RedUn]

so basically........higher = better

[jlm]

consider this:

it takes a bit of time for the compressed charge to ighite and develop full pressure in the combustion chamber. the point of spark advance is to give the pressure enough time to build so it pushes most efficiently on the piston just as it starts down after TDC. As you increase octane, you are inhibiting knock but also slowing down the burn, therefore you need more advance with higher octane fuel. It is not always true that more advance means more power; the advance needed is corellated to the burn time and octane rating.

[pocketrocketowner]

You can run retarded timing or normal timing with high octane fuel and there is no deleterious effect. If you want the benefit of higher octane you must advance the ignition, period, end of story.

[Babes]

What about fuel additives? are they worth while putting in or only if the car has been set up for higher octane as previously mentioned?

Jason

[pocketrocketowner]

Octane boosting additives are worthless. (See above)
Things that can be useful are valve and injector cleaning additives, specially if you are into using plain gas and not premium. BMW dealerships sell a valve cleaning additive that is the bees knees, thoroughly proven and thoroughly effective.
All US gasoline is sold with additive (though Regular has a minimum mandated content) while there is no obligation to use additives in Europe or the rest of the world----y'know, all them people worried about global warming and Kyoto can't be bothered to mandate a "known to work" emission mitigation technology
Anyways, off the soap box.....all premium grades the world over (reputable brands) contain very effective cleaning additives.