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It isn't about burn rate , which can be manipulated by chemistry . Lower octane ignites easier , and some dyno testing shows that an engine capable of running on 87 will make more power on lower octane than on higher octane . We have this discussion about every year or so , lots of confusion about what octane actually does , in the simplest definition , higher octane is more resistant to ignition , meaning higher compression ratios , usually meaning in modern engines CR ratios above 10.5 to 1 need a bit more octane to prevent pre-ignition . Older designs like a hemi-head Triumph run hotter than a modern design with more effective cooling . Gasoline will flash at 536 degrees F under zero pressure , ethanol at higher temps . Increasing pressure effectively lowers the flash point , as does the distance between the ignition source and the fuel mixture . The closer the ignition source , the lower the flash point . What this all means , octane requirements are dependent on several factors beyond just compression ratio . Dusty
I asked this engine devolopment engineer the question about fuel octane and power... David Redszus...http://www.precisionautoresearch.com/general%20info/WhoWeAre/PAR3.htm David Redszus » Mon Aug 26, 2019 12:11 pmNot true. Fuel octane has nothing to do with burn rate...nothing. Two fuels with the same octane ratings can easily burn at different rates. Burn rate is principally a function of inlet air temperature, compression temperature, squish velocity and engine rpm. Suppose we use a 100 octane, unleaded fuel on the dyno optimally tuned, and then add some TEL or TML to the fuel while it is running. There will be no difference in performance. The two fuels are identical except for octane.Of course, using the higher octane fuel would allow the engine to be tweake to a higher performance level without destruction due to detonation.If we are speaking about pump gas, then all bets are off since we do not know what the actual octane values, RON and MON, actually are. Neither do we have any idea regarding the actual composition and properties of the fuels.There is a reason why OEMs use very expensive certification fuels when performing engine tests; consistency.
Dusty, do you think Kevin Cameron has a good understanding about the combustion process in engines? How you ever watched his video I have posted here seevral times ? I will post it again... listen to what he says about the cause of detonation..Then you will understand what how higher octane prevents detonation... https://www.youtube.com/watch?v=aH-lDh3rVFQAnd this article written by a leading automotive emissions designer... http://www.contactmagazine.com/Issue54/EngineBasics.html using this info and understanding combustion, me,an average hobbyist mechanic, set several speed records with my 650 Triumph land speed race beating experienced guys with more higly tuned engines....
Nothing KC states contradicts what I said . Dusty
Both of the articles I linked give details about what higher octane actual does, not in general that it limits detonation...It's the details that matter if a person really want to understand the combustion process ...
Not arguing that , in fact I stated that in the simplest definition higher octane is more resistant to ignition . What I was stating is that burn rates can be altered with chemistry , independent of octane . All octane rating is based on is at what combustion pressure a given octane will start pre-igniting, based on testing with that cool little single cylinder variable compression engine , usually a *Ricardo* IC engine used in labs . Octane rating is nothing more than a number assigned to measure at what CR gasoline begins pre-ignition , the chemists then begin adding chemical into the gasoline until the process returns to normal , and the up the CR in the Ricardo engine until pre-ignition begins again , the add chemicals until the process once again returns to normal . Cameron is describing the difference between pre-ignition and detonation , a different subject than we are discussing . Dusty
In my years of developing aircraft air cooled engines I can say w/o doubt that if you have detonation (real) there will be damage in the top end, usually piston.Pinging is pre detonation. Stuff added to the fuel to prevent detonation lowers the energy content of the fuel slightly but that is better than destroying the engine.Good trade off. :-) Good point Mike . Detonation results from incomplete burn of the mixture during the designed time period . I mentioned before that the octane needs of an old Triumph engine VS a much more modern design are somewhat different . Back when engines were either undersquare or *square* , meaning the stroke dimension is either larger than or equal to the bore dimension , a hemi head with a large surface area was required to fit ever larger valve sizes . Those engines ran really wide included valve angles , and high dome pistons to fill up the cylinder head volume . Those high domes didn't cool very well , because they were not close enough to the cylinder walls to exchange heat . As the engineers who were working this out began building engines with oversquare bore stroke ratios , the natural result was more available surface area in the cylinder head , meaning the combustion chambers could be flattened out , valve angles became narrower , and pistons didn't need to be domed to fill up empty space to achieve high enough compression ratios for good torque production . The end result was better cooling and more effective combustion . Back to the Turner designed Triumph engine , it was an undersquare design , which meant high domed pistons , which run hotter . A 1400 Moto Guzzi is significantly undersquare , meaning a more flat top piston can be employed , which because of the fact it can transfer heat more efficiently , along with generally better cooling from an increased understanding of air cooling and because one head isn't heat soaking the other as in a Triumph from 1968 , at a given compression ratio , the Guzzi won't need as high an octane rating as the old Triumph . Whew , think I will let the brain rest Dusty
Cameron clearly states detonation is the spontanours combstion of end gases that burn far more rapidly, like an explosion...That "explosion" is ping sound you hear...The problem is not with the main burn... Did you read the Cline article?
Yes , but you are arguing something I never stated . In fact , higher octane than needed can lead to detonation , because it won't ignite at the designed time , meaning incomplete combustion . You seem to be indicating I somehow think I am smarter than Cameron , which of course is just silly , that guy knows more about IC engine physics than 99% of everyone . But we were discussing burn rates VS octane , all I was pointing out is those two are largely unrelated . Octane doesn't change burn rate . Dusty
Was not my intention to belittle your comments, sorry...yes you are correct that octane doesn't change burn rate so it should have no effect on power all else being equal...
I will say I'm all of this that butt dynos are notoriously inaccurate.
When a rider typically uses type ‘R’ gas and fills up with type ‘P’ gas and notices a difference; the butt dyno has at that point fulfilled 100% of its possible performance parameter. That the rider even felt or noticed a difference, when every other time just adding gas has resulted in no perceptible difference, again, at that point the butt dyno has performed 100% of its total expectation. Especially when there could have been an expectation of degradation but an improvement was felt instead.I don’t believe anyone has stated a butt dyno can perceive a particular percentage of a difference. Just that it can, and every rider should have some level of their butt dyno perceiving a performance change.Let’s say, unbeknownst to you, someone installed a fresh set of scrubbed in tires on your bike. Would your butt dyno notice a difference? I’d sure hope so.
The problem comes because we are talking about perceptions (feeling, noticing), and often because we are also expecting to feel or notice. It's often basically a placebo effect as much as we all want to believe we can feel and notice the slightest changes.
You were clear and I was saying we often fool ourselves into thinking we feel what we expect/want.No big deal... All good.
The real question is what tire and oil is best matched to the octane level you are running.
