Layman's guide to Octane By LUKE (Read 422 times)

[LUKE]

"Laymans Guide to Octane

1 - OCTANE is the resistance to detonation. High compression engines cause fuel to pre-detonate - this is called KNOCK. It is dangerous to your motor.

2 - Scooters (all that I'm aware of) use notoriously LOW compression engines. 87 Octane has been shown to be fine. In high altitude areas I've even run 85 Octane in my race scooter and it did not knock one bit.

3 - HIGH OCTANE does not equal "Clean" or "Power" - Running a motor designed for 87 Octane fuel on 92 will actually make it run poorly, less power and worse mileage. The detergent additives are specified by the company selling the fuel and they are consistent from 86 - 94 octane.

4 - If your Jaguar, Snowblower, JetSki, Scooter, weedwacker etc. runs fine on 87 Octane without knocking or running on after you turn off the key, keep using it. Keep in mind modern vehicles are designed to run on a WORLD of different fuel qualities. The worst fuel you can pull from a pump in the US is going to be much better than the best fuel you can pull from a pump in India etc.

5 - Octane is not Octane. The numbers we use in the US are based on an average of 2 different testing methods. The number found In most countries (including all of Europe and Australia) the octane that would be shown on the pump is the Research Octane Number but in the United States and some other countries the headline number is the average of the RON and the Motor Octane Number. So, the gas we call 87 Octane R/M is actually written in most owners manuals as 92 or 93 Octane (RON).

If not specified assume the Octane number in the manual is a RON number. As most vehicles (scooters) are not manufactured in the US.

Here is our "real world" application data:

In 1999 the Ohio Department of Agriculture conducted a test of 1000 gas stations. 85% Of these stations were pumping non-premium octane fuel from their premium pumps. Audits of these stations were conducted and it was seen as a regular practice for stations to have "Regular" account for approximately 82% of their monthly sales. Yet it accounted for over 95% of the fuel they ordered from their supplier. Unless they were giving away thousands of gallons of 87 Octane fuel, it was quite obvious they were selling the 87 out of the higher octane pumps.
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[wolfhound]

Thanks, Luke. there has been a lot of confusion on this question. I have run regular and
premium and could find no difference other than the savings when buying regular. Therefore
I believe that 87 octane is best for scooter motors.

[mauiboy]

That mostly matches my understanding but not always what I have witnessed. I do however agree with your comments.

Some oddities I have witnessed, on normal compression (9.2:1 for the gas, 18:1 for the diesel) car engines I have routinely noticed better results with BP ultimate as compared to BP normal grade fuel and it is actually marketed as giving better mileage (an extra XX miles per tank etc, for the advertising standards agency to allow it there should be some truth to it?), the same going for diesel with a higher cetane rating. Part of the explanation given is the better detergents etc, but this is from a european perspective rather than an American one so it is possible there are different detergents used. There are also usually only 2 grades + diesel available rather than 3 grades of gas and no diesel which is more common in the US. I have no proven explanation for why I have witnessed 10-15% better fuel economy on a normal engine but I have. Perhaps euro fuels do spec detergents etc differently between lower and higher octanes as they rarely have a mid level?
Second is that I believe it is common for 'plus' or 89/90 rated fuel to be a mix from the 87 & 92 fuels which may explain a little as to why there is more 87 ordered than sold directly.
Also why do scoots have a sticker stating 90 octane + required? I'm not saying it is, just curious. Do the engines lower tolerances play a part? More likely to knock due to the delayed spark or poor design? No idea personally just interested. What do you all think? I know a lot of scoots are in the 8-9:1 range but I have seen a few 150's in the 10:1 range but that could be bad maths / bad translation / cut and paste drop selling etc.

I'm thinking after a few more tank fuels I will switch down a grade and see after a few tanks of that what the results are?

As I said, not trying to whizz on anyones chips, just curious as to what I am seeing

Thanks for starting the thread, there are a lot of misconceptions around octane ratings and at its most baisc the whole higher compression needing higher octane is true, but perhaps the situation is clouded by gas companies marketing of higher octane fuels being 'premium' and pricing accordingly?

[mauiboy]

Interesting, dropped to 89 and my unscientific WOT up the hill test seemed to add a couple of mph into a stronger headwind than normal. I'll revisit in a few months when I have more mileage data. That is what I would have expected, but not what I have seen in the past.

[wolfhound]

I have found in the past that My Toyota Matrix ranbest on high test but that was what Toyota
reccomended for the souped up 6 speed unit. Lost milage and pep on regular. My wifes 09
Volvo requires high test and thsat is all she will uses. My Honda CRV is set up for regular so I
stick with it. I switched to regular on all my scoots, most of the folks that I ride with run regular, and none of has found any difference in performance. I think that Lukes opening
post is correct.