Octane Ratings and what they mean

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infil
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Octane Ratings and what they mean

Post by infil » Thu Oct 04, 2007 2:40 pm

Ok, quick simple breakdown, Octane is fuel's resistance to ignition.
Higher the octane, the harder hte fuel is to ignite, so no, 116 does NOT burn hotter than 91 octane, it takes a helluva lot more energy to ignite.

To get the most power out of your engine, run the LOWEST possible octane you can get away with, without detonating.
The reasons you would run a higher octane fuel are turbo/high compression engines due to the increased cylinder pressure.

As cylinder pressure increases, friction from the air/fuel charge being compressed increases and this raises the temperature. That temperature increasing will cause lower octane fuel to ignite before the spark plug actually fires. Preignition will absolutely destroy an engine. It puts tremendous pressure on the rod and rings, and extreme preignition is capable of shoving rods right through pistons.

Other reasons are in cases where extremely lean conditions will be seen, as in the case of nitrous. The way nitrous works, it adds extreme ammounts of oxygen to the mixture, tipping air fuel ratios well into the 15-16 range, and again, as that temperature increases so to do the chances for pre-ignition.

At the opposite end of the spectrum, too much octane means the car will run poorly, if at all. If you put c16(116 octane race fuel) into a stock neon, the chances that the car woudl even be able to fire the mixture are slim., however 100 octane is usually something that can be done, however it will still cause a loss of power that can be pretty detrimental.

All in all, mixing 93 and 100 in a 50/50 can be done and will generally help if you have a computer that pushes alot of timing, however it is again, a fine line that can only accurately be determined on a dyno. Injectors, pressure, pulse width, and valve/ignition timing will have a much more dramatic effect on power than overdoing it with too much octane.
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Post by SYRYS04 » Tue Jun 16, 2009 9:34 am

so I've been tryin to tell people that usin higher octane isn't goin to increase performance on a car wit all factory parts especially those with n/a engines.... I'm still in the green right, I am correct right? Cus when u get a car that says use 89 or 91 unleaded only then THATS what you should use, if not all your doin is wastin money right.

Cus I see it like this, if u got 2 of the same cars next too each other. One car wit half a tank of 89 and the SAME car wit half of tank of 91 and you race both, you gotta be a super genius to automatically kno which is which, right?
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Post by ahmedoth » Tue Feb 09, 2010 5:00 pm

ive got a 02 r/t stock....what should i use?
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Post by racer12306 » Tue Feb 09, 2010 5:09 pm

For maximum performance you want to use 92 octane (using the R+M/2 method)
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Post by ahmedoth » Tue Feb 09, 2010 5:22 pm

racer12306 wrote:For maximum performance you want to use 92 octane (using the R+M/2 method)
thanks boss...
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Post by occasional demons » Tue Feb 09, 2010 5:49 pm

racer12306 wrote:For maximum performance you want to use 92 octane (using the R+M/2 method)
But you can safely run 87 R+M/2

You just won't get "maximum performance" But may get better mileage. I find I can do better with 87, but it just may be that I don't have the same power to "feed into."

Just so you know, I am running an '02 R/T PCM. I just don't have 3.91 gears. Yours may actually have an advantage, in that the PCM won't need to pull timing as much, due to the lighter gearing load.
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Post by nerox » Sun Mar 07, 2010 5:53 am

What are the Octane ratings you can get in the usa?

im sure i heard somewhere its like 89 91 and 93 or something?

in Great Britain the normal is 95 and then high octane usually 97 or 99
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Post by racer12306 » Sun Mar 07, 2010 10:31 am

We have, generally, 87, 89, 91 octane using the R+M/2 method. The UK uses the RON number only. I think the US is the only country to average the RON and MON numbers.

There are higher altitudes that have 85, 87, 90 or something like that because the extra octane isn't needed at altitude (and I mean up around 5500ft)

Sunocos generally have 94 octane and a few select Sunocos have 100 octane unleaded race fuel.

Remember these numbers are all R+M/2.
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Post by heydockyle » Sun Mar 07, 2010 10:36 am

There is a gas station called Freedom Fuel around me that sells 104 or 106, can't remember..
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Post by racer12306 » Sun Mar 07, 2010 10:39 am

Are you allowed to pump it into a street car?

leaded or unleaded?
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Post by heydockyle » Sun Mar 07, 2010 2:28 pm

racer12306 wrote:Are you allowed to pump it into a street car?

leaded or unleaded?
Yes you are allowed. I am pretty sure it is unleaded. My buddy had an srt-4 and we ran it in his car some. Boy was the power nice.

You are also allowed to buy jet fuel from an airport up here, but it has to be pumped into containers.
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Post by racer12306 » Sun Mar 07, 2010 5:03 pm

Probably not actual jet fuel, probably avgas which is commonly used in smaller prop planes.

My dad used to use it in his race car for the oxygenation and the higher octane.
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Post by heydockyle » Sun Mar 07, 2010 5:20 pm

racer12306 wrote:Probably not actual jet fuel, probably avgas which is commonly used in smaller prop planes.

My dad used to use it in his race car for the oxygenation and the higher octane.
Yea, you're probably right. It's 108 octane if I remember correct. Ran it in the dirtbike some.
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Post by racer12306 » Sun Mar 07, 2010 5:28 pm

Yeah, that's avgas.

Jet fuel is glorified kerosene, essentially.
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Post by neon krazy419 » Tue Mar 30, 2010 7:40 pm

this is really interesting my friends always say go higher octane now i never will lol!

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Post by OB » Wed Mar 31, 2010 4:29 pm

neon krazy419 wrote:this is really interesting my friends always say go higher octane now i never will lol!
From what I've seen, you have a bunch of friends who have no idea what they're talking about. :roll:


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Post by Marmelade Boy » Thu Jun 03, 2010 8:29 am

OB wrote:
neon krazy419 wrote:this is really interesting my friends always say go higher octane now i never will lol!
From what I've seen, you have a bunch of friends who have no idea what they're talking about. :roll:


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