high octane gas or low octane gas

[Jayraye39]

So I have always ran 87octane gas in my bikes. But just for fun I decided to run a tank of 93octane. Not a good choice. The motor actually lost a bit of top end and the throttle response was so bad that i thought I had cracked a piston ring or blew a case gasket. I also was getting back fire every now and again. It sounded like it was coming through my carb. My thoughts were that the 93 gas burns so much slower that during the down stroke the combustion would ignite the fuel in the case via the transfers as soon as they opened. needless to say I though I had a major problem so i tore down the top end only to find nothing wrong except for a unusuall amount of carbon build up on my piston crown. in my findings 93 octane is horribly bad for these small motors. stick with 87-89. Anyone else ever had similar symptoms with high octane fuel?

 

[Jayraye39]

I know it was igniting fuel through my transfers because both sides of my piston are brown.

 

[Whitewill1412]

That's wild. I wouldn't have thought that the more expensive gas would make the engine run poorly. Live and learn

 

[DAMIEN1307]

My thoughts were that the 93 gas is so flamable

High octane is actually a slower burning gasoline than 87 octane...The higher the octane number, the more compression the fuel can withstand before detonating.

I also use 87 octane but it is Ethanol-Free...Refineries actually use ethanol as an octane boost in gasoline...Despite the gas pump saying it is 10% ethanol, it is now at 15% ethanol content thanks to the EPA jacking up the amount to be used in both the winter and summer mix.

Octane used to be boosted with the use of Tetraethyl lead, and as we all know, leaded gasoline is no longer in use for vehicles used by the public.

 

[GW's Motorized]

It could be that your engine is tuned to run on 87 and not 93.

 

[DAMIEN1307]

It could be that your engine is tuned to run on 87 and not 93.

He would have to have a much higher compression motor to run high octane gasoline...These China Girls do not attain these high compression outputs unless they are heavily modified racing engines.

 

[MechMike219]

I run Sunoco GT Plus 104 in my ported Chinarelli. The head has also been tampered with, higher compression cc and wider squish band. But wait... theres more..

i now have slight adjustability to my ignition timing, not much but a couple extra degrees advanced definitely helps with propagation. lol.. big words make it seem more legit.

why 104 you might ask... well... cuz i can.. and as highly oxygenated as it is, if it sits for a period of time like 2-3 weeks, it doesnt turn into something i wouldnt even use to start a fire with. but if my gallon or 2 sits that long theres cause for concern cuz i didnt buy it to store it..

as far as a stock or slightly upgraded motor goes, 87-93 is absolutely fine. just tune to what youre running and never expect your tune to work with any changes you make. that 104 is sooo pretty lookin too, its blue from all that oxygenation lol. if you think this is overkill now, wait till xmas when i splurge on the VP Racing T2 5gal pail of premix.. $105/gal and $90 for shipping. im dumb like that

 

[ImpulseRocket]

High octane is actually a slower burning gasoline than 87 octane...The higher the octane number, the more compression the fuel can withstand before detonating.

I also use 87 octane but it is Ethanol-Free...Refineries actually use ethanol as an octane boost in gasoline...Despite the gas pump saying it is 10% ethanol, it is now at 15% ethanol content thanks to the EPA jacking up the amount to be used in both the winter and summer mix.

Octane used to be boosted with the use of Tetraethyl lead, and as we all know, leaded gasoline is no longer in use for vehicles used by the public.

High octane unleaded fuel burns more slowly as the octane number increases. Leaded fuel actually doesn't suffer from that as the TEL itself increased octane rating without requiring longer chains of hydrocarbons that are used to create unleaded high octane fuel. Just ignore the birth defects and shortened lifespan from heavy metal poisoning.

 

[Karl Snarl]

Let me clear this up. I can't take it. High octane gas burns at the same rate. It is just able to resist ignition more than a lower octane. Think of it like this. Low octane can be set off like a liberal. It's easy to get burning down a city. High octane takes more pressure ( heat ) to crack the molecule to release it's energy. High octane is like a Queens guard, takes a bit to get them to set off, but they will fire off and burn you down just as fast a liberal.

 

[ImpulseRocket]

Let me clear this up. I can't take it. High octane gas burns at the same rate. It is just able to resist ignition more than a lower octane.

Higher octane unleaded fuel does ignite slower when presented with the same conditions as a lower octane version of it.

Maybe the idea of a "slower" burn doesn't sit well with you, how about a more controlled ignition process. Same energy content, but less volitile under the same conditions, and more stable under harsher conditions, thus making it less prone to pre-igniting.

Slower is just a generic place holder because of the increased amount of input energy required to break the increased number of covalent bonds. aka, Laymans terms to help the average person who doesn't understand the chemistry and physics behind what the real difference is.

This is an article in Motor Trend that explains it. Here

MIT even gets a word in edge wise. MIT Here

I can pull up an article from Sunoco and a few other fuel companies if you like.

You have to qualify the type of fuel, and since most of us run on unleaded pump gas. higher octane = slower ignition in the same conditions as lower octane.

Engineered race fuels with special additives or substitute lead compounds, AV gas, and/or actual leaded fuel can ignite at the same level as the lower octane fuels of the same type because they share the same hydrocarbon chain lengths, and the additives affect their anti-knock characteristics. This is also why race fuel tunes and pump gas tunes tend to use wildly different ignition advance profiles. "Fast" burning high octane race fuels will grenade an engine with the same kind of timing higher octane unleaded punp gas can/needs to run.

This is my knowledge from years of ecu fuel and ignition map tuning on race and road applications speaking. I have seen and taken part in some interesting dyno sessions over the years, including one we did to show customers why putting 93 octane unleaded in their 1997 Honda Civic didn't actually add horsepower. In fact, it lost power vs. running just regular 87.