Author Topic: Petrol type?  (Read 466 times)

Offline Johnny J

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Petrol type?
« on: 08.02. 2015 20:43 »
I just wonder which "RON" octane rating is best for our bikes?
In Sweden we have 95 or 98 Octane.
   Gothenburg, Sweden

Offline muskrat

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Re: Petrol type?
« Reply #1 on: 09.02. 2015 05:19 »
G'day Johnny.
Depends on your compression ratio. Anything under 9:1 95 is great. Over that I use 98 and on the cafe and I bump that up to 105 *eek*. The low comp bikes (6.5 - 7.5:1) 91 is more suitable (they'd run on kero). The higher the octane the slower the burn so ignition needs to be advanced which leads to the problem of pinging.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
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Re: Petrol type?
« Reply #2 on: 09.02. 2015 07:59 »
I agree with Muskrat about octane ratings, but is Ethanol a consideration Johnny? Most 95 octane here in France (and elsewhere?) is now "E10", ie 10% ethanol roughly. Loads of quite scientific/chemical reading out there if you can be bothered.
Depending on what or whom you believe, the stuff rots fuel lines and can eat some bits of carburettors.
I've replaced most of the fuel lines on my bikes in recent years with modern, whether as result of the new brew or not I don't honestly know - but they had gone mushy/rotten from the inside and bits were blocking filters. No carburettor parts have been eaten as far as I can see. 
Anyway, whether out of paranoia or for better reasons, I use 98 in everything old nowadays unless there isn't a 98 pump on a forecourt.

Haven't had pinging problems myself, but I don't have anything higher than 8.5:1 these days and my A is bog-standard iron Flash-spec.  A highly tuned twin of another marque, running at 10:1+ at one time, was fine on 98 at standard ignition settings. A lot of it must come down to cylinder head design I guess.
Super Rockets etc seem to me to be a bit more sensitive to pinging than some other engines of similar compression ratio. I am influenced by the findings of Orabanda (published on here) regarding optimal ignition advance/power after extensive rolling road tests. Less than 'book' max advance seemed to work best, advice I have followed ever since.
Cheers, Bill
Bill

Offline muskrat

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Re: Petrol type?
« Reply #3 on: 09.02. 2015 09:22 »
Down here ethanol is only in the 91 fuel at the moment but I did see a 95 pump with an ethanol sticker on it at Goulburn.
The A7/10 combustion chamber shape plays a big part of the pinging problem if high top pistons are used.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
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Offline cyclobutch

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Re: Petrol type?
« Reply #4 on: 09.02. 2015 11:12 »
Yeah, I use 'high' octane in the hope of missing out on ethanol.
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Offline Johnny J

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Re: Petrol type?
« Reply #5 on: 09.02. 2015 16:38 »
OK, in our 95 there is 5% ethanol and in the 98 there could be up to 5%, but normally lower than that, sometimes 0%.
So if the the bikes runs fine on 98 it's preferable, right?
   Gothenburg, Sweden

Offline muskrat

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Re: Petrol type?
« Reply #6 on: 09.02. 2015 18:41 »
Right.
Enjoy it while you can, eventually ethanol will be in all our fuel and in increasing %'s.
I still have my methanol carbs for the cafe, but at 12 miles peg gallon and $5.70/gal it won't be out much.
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
Australia
Muskys Plunger A7