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Discussion Starter #1
Hi,

Here in the uk we have a choice of octane fuels, my question is would my scrambler benefit from using higher octane petrol? I have used it before and the bike felt a bit more vibey!

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My dealer said "Don't bother" with super unleaded when I picked my Icon up, but I once had to use it when my local garage was out of regular. I must say it felt smoother at low revs with the hot stuff, so I've been using it since. I get better fuel economy, but this is of course offset by the higher cost per litre, so the cost per mile is the same.
Jonny
 

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IMO, the higher the better.

I use 93 exclusively in all my engines. It burns cleaner and seems to have a bit more "oomph".

Worth it? Probably not, but I sleep better at night.

Cliff
 

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IMO, the higher the better.

I use 93 exclusively in all my engines. It burns cleaner and seems to have a bit more "oomph".

Worth it? Probably not, but I sleep better at night.

Cliff
This is totally false...

Higher octane fuel does NOT burn "cleaner", nor contain more energy potential.

It exists to prevent pre ignition in high compression scenarios. It burns "later", not more powerfully.

For best performance you should use the MINIMUM octane reccomended. For the Scrambler, that is 90 octane fuel (R+M\2 method, which is what is used in the US).

In Europe, which uses the RON method of calculation, one should use 95.

Anything higher is actually giving you LESS performance, and costing you more too.


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Since getting my Icon a couple of weeks ago I have been using Shell 93 and the bike runs great. So they have an 89 octane and that should be fine?
 

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Since getting my Icon a couple of weeks ago I have been using Shell 93 and the bike runs great. So they have an 89 octane and that should be fine?
No, 90 is minimum (in the US, 95 in Euro RON).

If the choice is only 89 or 93, then use 93. In many parts of the country 91 is available, which would be better - and less expensive.

Always use the measure of octane closest to the MINIMUM (but not below) recommended for best performance and economy.

Running fuel with a higher octane rating will not damage anything, but will not yield any benefit. Quite the opposite, it will actually hurt performance.

The only exception is if one would raise the compression level of the stock motor, which would then require higher octane in order to prevent pre ignition.


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That was my thought as well. I use to use to drag race cars and octane was critical, as you say for high compression or boosted engines. Will have to stick with 93 here as you don't see 90 or 91 in the area.

One last question. Looking at several slip-on exhausts. In every case, regardless on which one I choose, a tune is necessary?
 

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Here in Florida it's only 87, 89 or 93, so 93 it is since the minimum is 90. There's a couple ethanol free gas stations that have 90 which I prefer, but the 2 closest stations are about a 30 minute trip one way for me.


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Discussion Starter #10
Thanks for all your replies and Tony you always come up trumps, I recon you are bang on as I felt more vibrations and genuinely felt it lost power, thought it went this way but just needed clarification. Cheers boys.

Armo
 

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One last question. Looking at several slip-on exhausts. In every case, regardless on which one I choose, a tune is necessary?
If your choice is an exhaust that eliminates the catalytic converter (most likely scenario in the US), then yes - fueling adjustments are absolutely necessary.


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This talk about octane reminds me of back in the seventies when I used to smoke and had a Zippo lighter. Occasionally the Zippo would run out of fuel when I was out on a run so I'd top it up with petrol out of the bike. Back in those days petrol in the UK was designated as 5 star (101 Octane), 4 star (98 octane), 3 star (95 octane) and 2 star (92 octane). These were all European ratings.
What I particularly noticed was that the higher the octane the harder it was to light the Zippo. 2 star was by far the best.
I never thought about all that lead I was probably inhaling at the time. Fortunately, I've been stopped smoking for well over 30 years but I still have the Zippo lying around.
 

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When singer Gram Parsons OD'd way back when, his manager took his body out to the desert for cremation. He bought a gallon of high-test because he didn't want him to "ping".

That's the truth, Tony!

Cliff
 

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What I particularly noticed was that the higher the octane the harder it was to light the Zippo. 2 star was by far the best.
I never thought about all that lead I was probably inhaling at the time. Fortunately, I've been stopped smoking for well over 30 years but I still have the Zippo lying around.
This makes complete sense, as the higher the octane rating - the more it is resistant to combustion.

In a high compression scenario (motors with as-designed high compression, or those using forced induction) lower octane fuels can combust prematurely (prior to the spark, by the heat of compression alone), causing poor performance and engine damage. You will see many high-performance vehicles specify "premium" fuel (higher octane), this is to prevent this problem.

Running HIGHER octane fuel than that which is specified causes no damage (other than to your wallet, along with decreased performance), but running LOWER than specified opens you up to the possibility some pretty severe motor damage.
 
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I usually fill up with Chevron Supreme which is the highest octane at their pump, mainly because most of the year the temperature is fairly high in our area. I guess I could try a lower middle octane fuel but when the weather is warmer I worry about detonation but maybe I shouldn't?
 

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I usually fill up with Chevron Supreme which is the highest octane at their pump, mainly because most of the year the temperature is fairly high in our area. I guess I could try a lower middle octane fuel but when the weather is warmer I worry about detonation but maybe I shouldn't?
No, you shouldn't... Ambient temperature has no bearing on which octane to use.
 

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Once again, Tony, you are a wealth of information.

Since my earlier, uninformed post, I did a little reading-up on what the different ratings mean and you are absolutely correct with regards to compression and combustion among the various octanes.

One question, though- could our engines, even if not turbo or super charged, be considered "high performance", and if so, benefit from higher octanes?

I still want to use 93 just to sleep better.

Thanks in advance...

Cliff
 

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Once again, Tony, you are a wealth of information.

Since my earlier, uninformed post, I did a little reading-up on what the different ratings mean and you are absolutely correct with regards to compression and combustion among the various octanes.

One question, though- could our engines, even if not turbo or super charged, be considered "high performance", and if so, benefit from higher octanes?

I still want to use 93 just to sleep better.

Thanks in advance...

Cliff
Cliff,

There is no "benefit" from using a higher octane fuel - other than to prevent pre-ignition caused by high compression. The compression of a stock Scrambler 803cc motor is 11:1, higher than your average passenger vehicle, but not high enough to warrant anything above 90 octane.

Most passenger vehicles (normally aspirated) have compression ratios in the 8.5:1 to 10:1 range, hence they are fine using 87 octane fuels.

92 to 93 octane fuels are usually only required in motors exceeding 12:1 compression or those utilizing turbo or super charging.

If it helps you rest easier, than 93 octane will not damage your Scrambler (just your wallet), so you can use it - but expect lower performance.

*** Please note: all reference to octane numbers in this post is made using the US method (RM/2), Euro rating system (RON) is different! ***
 
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Tony, what is meant by lower performance when using higher octane fuel on our Scrams?

Around here, we have 91, 93, 95, 97 RON but all laced with 10% ethanol. Isn't ethanol harmful in terms of water build up? In major cities, we have pumps that offer 100 Euro 4 compliant fuel with no ethanol. I been using this 100 Euro 4 in all my bikes.
 
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