91 octane

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Pinger

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Yep. It wont help.
A fuel octane rating is basically its resistance to igniting.
The higher the number, the longer it takes before the burn starts.
Higher octane is used in high compression engines to give a fraction of a second of delay before the fuel ignites.
This allows the cylinder to reach full compression before ignition.
That is why running low octane in a high comp engine causes "pinging"
The low octane fuel ignites before the cylinder is at full compression and before it reaches the correct point in the timing sequence.
The opposite happens when you run high octane in a low comp engine.
The high octane ignites after the cylinder has reached full compression and that ignition happens late in the timing sequence.
And of course these engines were not designed with ethylated fuels in mind so that adds another little kink into the theory

None of the above is true.
Higher octane fuels have a reduced tendency to spontaneously combust - which prevents the last of the charge self igniting when it encounters the pressure wave from initial combustion before it encounters the (too slowly) advancing flame front which should be it's ignition source.
 

Pinger

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FWIW.... I ride a 2002 Kawasaki ZRX 1200. About 115 HP and 65 ft# of torque. I normally burn 87 octane ethanol bearing fuel. Stock jets and exhaust except the muffler has been gutted into basically a glass pack style. Didn't do anything for HP as all the restriction is in the header.

OK, to the point. I thought I would try some 91 octane fuel as this is a fairly high performance engine. Can't hurt, right... Well it did hurt fuel mileage. Not a lot. Only a couple MPG. Asking around it is confirmed with this engine/bike.

As it was explained to me the 91 fuel burns slower with less peak pressure as the engine is not set up with enough compression to warrant that fuel. So in reality a little less HP which demands a larger throttle opening which used more fuel ETC. Maybe a bit over simplified explication but it gets the point across.

Of course not every engine will respond in the same way. YMMV

Ken

The high revving (17-18,000 rpm) multicylinder race engines of the 1960s with very small cylinders needed no more than octane numbers in the 60s - akin to paraffin/kerosene.
At such elevated rpm there just isn't time for detonation and the small bore size meant the flame path had very little distance to travel before combustion was complete.
Low rpm and large bore diameters are where detonation can be much more problematic.
 

Hipster

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Yep. It wont help.
A fuel octane rating is basically its resistance to igniting.
The higher the number, the longer it takes before the burn starts.
Higher octane is used in high compression engines to give a fraction of a second of delay before the fuel ignites.
This allows the cylinder to reach full compression before ignition.
That is why running low octane in a high comp engine causes "pinging"
The low octane fuel ignites before the cylinder is at full compression and before it reaches the correct point in the timing sequence.
The opposite happens when you run high octane in a low comp engine.
The high octane ignites after the cylinder has reached full compression and that ignition happens late in the timing sequence.
And of course these engines were not designed with ethylated fuels in mind so that adds another little kink into the theory
Pre-ignition and detonation are two different things although extended detonation can also cause pre-ignition. Pre-ignition is caused by a hot spot igniting the fuel before the spark gets there. Higher octane burns slower not later.
 

RichLo

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Wow, theres a lot of bad info in this thread

https://www.bellperformance.com/blog/bid/101182/What-Does-Octane-Do-In-Gasoline-Octane-Ratings

Simple answer about octane is your wasting money putting anything but 87 in it.

and Short answer about 'Top Tier' gasoline is that its a marketing gimmick. Try to find an actual scientific study that shows technical proof that there is anything different than 'normal' gas.

If you want to do an Italian tune-up, throw a bottle of seafoam in your tank every other fill up.
 

thegawd

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thanks agIn for the info guys.... top tier is no gimmick though. it is much cleaner because it is more thoroughly processed, then in the case of Shell, V power Nitrogen Enriched, there are cleaning detergents added and, no ethanol.

that's the most important info for me right there... NO ethanol. that's really what I'm after.

this particular fuel is refined locally, and I personally know tonnes of people who work there and in the petroleum industry, labourers, computer guys and engineers who build the plants, (I have rich friends LOL, we are not) so no I dont have scientific papers but I do have "inside information" I only buy shell and this is a result of getting bad gas years ago that made my old burb run like **** with water in the fuel.

heres a screenshot from shells site, this fuel is the best shell has ever made, partnered with Ferrari.

Al

You must be registered for see images attach
 
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RichLo

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Soooo they pump nitrogen in the condenser when they refine it. Everything else in their statement can be transferred to any other non-ethanol 91.

Just sayin... vague claims are how marketers get paid.
 

Postmech

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High octane gas has less heat energy(lower BTU content) in it because they use lighter solvents with higher ignition points and slower burn rates. Used to help build refineries, petroleum engineers everywhere that loved talking about stuff like that. The alcohol used in the blend has at best 75% of the BTU's that gasoline has but has an octane rating of about 106. Lower BTU's, less fuel mileage. Engines built to run only on E85 can have much higher compression to increase fuel mileage and power but still lose fuel mileage compared to similar gasoline only engines. What I am trying to say, if your engine is designed to run on 87 octane, there is no benefit from using higher octane without a different tune up. Just info.
 
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