Yeah, that or Shell Optimax. _________________ MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
It's so much hassle at the moment, Optimax is about as best as you can get but check your jetting as it's density can effect the mixture. If you run premix it's the same sort of deal. Mix the oil with the fuel before the carb and it leans the fuel / air mix off a bit. I feed all bikes / cars nothing but optimax - works well especially if you are running a bit of extra ignition advance.
Avgas is readily available for high compressing motors and nice and cheap if you can find a supplier who will sell it to you without the tax just don't forget to consider some phosphour bronse inserts to the squishies.... or there could be tears before bedtime.. _________________ These aren't the droids you're looking for.
lol thanks Andy, I will say Shell Optimax is not the way to go with lightly tuned engines, "tests have shown up to a 2bhp loss compaired to standard unleaded". Anyone with knowlege of calorific values will understand why Optimax will lose power on this type of engine.
Stick to a normal unleaded or super unleaded. If your bike doesn't pink or knock on unleaded there is no point going super. All you are doing is buying fuel which effectivley burns slower and will produces less power. If you do suffer from pinking then yes you need a fuel with a higher C.V. or RON rating. Most of our bikes here, even the race ones, will be fine on bog stock unleaded.
Like blinka says tho, if you're running a little more advance, that sometimes can push the detination point of fuel a little too close, so a higher spec fuel is needed. But you can often get away with at least 2deg advance and raising the C.R a ratio before it's needed. _________________ If I have to take the carbs off once more...
StephenRC45 wrote:from pinking then yes you need a fuel with a higher C.V. or RON rating. Most of our bikes here, even the race ones, will be fine on bog stock unleaded.
Interestingly, I had been running Super Plus, but went Oop North to do a trackday at Croft, where I could only get normal unleaded. I siezed after a few laps.
The trouble is of course, you don't really know how close you are, and when racing you like to be as safe as possible... _________________ MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
I've been running super plus too. I have no doubt you are right Stephen, but like Dave I like peace of mind when flat out past a line of cars. and if it does go bang, at least you can rule out the fuel from the list of what the f%*k caused that
I thought everyone had the skinny on this?
It's simple enough:
If you are running more compression, or ignition, you may see the benefit of a slow burning 98RON.
Otherwise, you'll get more grunt out of good quality 95RON - properly set up.
And one last thing - it is WAY easier to do a plug chop on 95RON. You may want to think about that.
Clarkie wrote:And one last thing - it is WAY easier to do a plug chop on 95RON. You may want to think about that.
Good call Clarkie!
I've always used Esso Super whenever I can get it, but that was more to do with the fact I was once told by a source that I trust that it is a very well refined (i.e. good quality) fuel.
On the last rebuild I did notice a very small amount of detonation on the lower cylinder head, but the fact the motor has covered about 20,000kms with all manner of jetting (in the name of research!), it's hardly surprising!
OK, I just have to speak up here as this is a pet peave of mine.
Higher octane fuel does not "burn slower". The octane rating is NOT what determines the burn rate. Octane level determines what level of compression the fuel can take and still resist DETONATION.
The fuel composition is what determines the burn rate. They make alot of race fuels specifically designed for different engines. To be an effective race fuel, it needs not only the proper octane level, but the proper burn rate for the application. The burn rate should be different depending on the peak RPM of the race engine (lower peaks require a lower burn rate). This is why Aviation fuel is a poor choice. It may have the proper octane level, but the burn rate is designed for engines that dont turn faster than 4,000 rpm. Most gasoline airplane engines run around 2500.
So the dregs from Morrisons supermarket should be okay then yeah? _________________ MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
Before anyone goes any further, I'd like to say that it's actually very pleasant and refreshing to see people discussing the subject and not getting nasty - top dollar !
I knew that the octane rating did not effect the burn rate but I'm not exactly an expert or able to discuss it much.
I can tell you that higher compression and some ignition advance is a good way to releasing more power from many 2 stroke engines. I run a highly tuned Yam twin that, with it's full compressing head, will not run anything except avgas or shell optimax if avgas is not available. It's peak power is at 11750rpm so although the thing about avgas not being for low revving engines may be true in certain applications ie - the fact is true, in reality the bike thrives on it / needs it to run without lunching itself.
Suck, squeeze, bang - blow..... sounds like a cheap whore ! _________________ These aren't the droids you're looking for.
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just don't forget to consider some phosphour bronse inserts to the squishies.... or there could be tears before bedtime.. 
