The truth about 100 octane ECU's...

[float_6969]

The truth is that they are generally not tuned for any higher grade fuel than the 93 octane that you can get right here in the good ole' USA. The difference is in how octane is measured.

There are two different ways that octane is measured for internal combustion engines. RON and MON. RON stands for Research Octane Number. MON stands for Motor Octane Number.

Before explaining the difference lets discuss some backround information on fuels in general. First of all, the term octane, in this application anyway, is a measure of a fuel's ability to resist autoignition. At any given point there is a mixture of different molecules of hydrocarbons in gasoline. Some molecules have very low octane levels while some have very high octane. This mixture works out to an average octane level.

Here is where the different measures come in. The RON is derived from running the given fuel through an engine under variable conditions to determine how it behaves in relation to a given constant fuel, which is a mixture of isooctane and n-heptane. (eg: a mixture of 60% isooctane and 40% n-heptane = and octane rating of 60) This is applicable to ANY combustable material, not just gasoline. Remember though, this is just a measure of the fuels ability to resist autoignition.

MON is tested in much the same way the RON fuel is tested, but they basically put the fuel under more "strain" and because of this the MON number will tend to be lower than the RON number.

This is where the confusion comes in. Europe and Asia both use only the RON. Because of the difference between the two ratings the US and many other places in the world use the (R+M)/2 method {[RON + MON]/2}. This gives the mean between the 2 octane ratings, and because the MON tends to give a lower number than the RON, drops the mean octane down to the leves that we see here in the US.

You're getting the same gas, it just has a different rating on it.

For more detailed info check out Wikipedia HERE.

[r34 gtr]

ha! i knew that already. i still use it as an excuse for when my car runs terribly though.

[dvd]

damn, we still dont have 93 octane over in the sf bay area -=[

[float_6969]

We don't have 93 in the midwest either. 91 is the best we can get.

[ceniack]

there is one shell station here in okc that i know of that has 93 octane, they also have 101 at the pump :-D

[r34 gtr]

aaah, just filled the car up with some chevron 93, you know, because we get that here. so hows that 91?

[fitch9014]

i used to live close to maryland and they had a couple of sunoco (sic) stations in the western part of the state with like 94 and i think like 104 near the drag strip. for the peeps who've got the 91, can you guys just use an octane booster when you fill up? i mean, 91 doesn't make the car ping under heavy loads does it? you know, lots of boost, heavy throttle, etc... as far as i know VA is still a red state, so i'm actually kinda suprised we don't have leaded fuel anymore...

[float_6969]

It works alright. I was able to tune my high compression CA to not knock on pump gas.

I'm running VERY little total timing under boost, but it still works pretty well.

[tyrannix]

try cutting your pump furl with low lead airplane fuel (i forgetwhere the idea came from, maybe somebody on here)

but I plan on playing with different fuel mixes (one of the reasons i went with megasquirt, the ability to save and load fuel maps very easily)

ingredients -

87 pump fuel91 pump fuel100ll airplane fueltoulene (sp?) if i can get it in gallon or better increments

other ingredients as i find what kind of detonation resistance they provide

and try out different mixes

BTW - read the package on those octane boosters - 'it wil raise your octane rating by 1 point *** '

then somewhere else it defines 1 point as 0.1 octane rating

CJ

[float_6969]

I've used toluene on multiple occasions. It works great.

[fitch9014]

there was some write up in scc magazine about the performance increase from using fuel additives. basically, it was how to get the most bang for your buck. if memory serves, toulene is the main ingredient in most of the additives on the market anyway, so it's not a bad way to go to cut crappy fuels. however, and the article went into more depth on mixes, there's a certain percentage point in how much actually makes more power and the point where you're just wasting money...you know, now that i think about it, is there any particular reason for the varying grades of high octane in certain states? i mean, it seems to me, that a higher octane in "an engine that could benefit", would be cleaner burning and more efficent, therefore easier on the wallet and the environment, not that any of us care about that or anything...

[LongGrain]

thats because most cars arent designed to run on 91 or 93, their made to run on 87. when you put 91-93 in MOST cars it doesnt all get burned which leads to catalytic converter failure and possibly extra pollutionz0rz

[tyrannix]

thats because most cars arent designed to run on 91 or 93, their made to run on 87. when you put 91-93 in MOST cars it doesnt all get burned which leads to catalytic converter failure and possibly extra pollutionz0rz

thats not really correct

more octane = more detonation resistanceif youre running an octane rating higher than you need, it is only wasted money, thats all - It wont run richer or anything

as far as i know anyway, somebody prove otherwise, im always up for further learning

CJ

[float_6969]

For the most part you're right. The problem comes from when they start doing things like blending ethanol into the fuel. Yes, it yields you a higher octane fuel, but you're getting less energy released for a fixed volume of fuel. Now when you're in closed loop, it doesn't matter, as the ECU just listens to the O2 sensor and adjusts the fuel accordingly. You'll get slightly worse gas mileage, but that's about it. The problem can come when you're under full load and it's a mix. Depending on the mixture, you can run too rich or too lean. Too lean is very unlikely as stock ECU's often have overly rich mixtures programmed in at full load to compensate for the varying fuel mixtures.

Remember, octane is simply a measure of the fuels ability to resist auto-ignition. It's NOT a measure of the amount of energy that a fixed volume of that fuel has available to release.

Ex: 1 Gallon of 87 octane pump gas has more energy available than 1 Gallon of 95-105 octane E85.

[rexhunta]

so we can get 98ron here in Australia, thats close enough to the 100ron they use in Japan?

as most our major service stations ( BP, Shell) all sell a 98ron mixture.

But one thing i do find when i use Shells 98, is thjat my plugs go a burnt orangey colour, like red house bricks, but when i use BP 98, it goes the usual lighter brown colour, kinda like the bottom of the frontbar in floats signature picture.

[float_6969]

I wonder if Shell is still using MTB in Australia? I'm a firm believer that different fuels make the car run differently, and I only run fuel from BP.

[rexhunta]

not sure on that MTB, but i only ran shell once to see that colour come up, and have never run it again. Car was about to go on the dyno and we were checking plugs, and saw that colour on them. so i took i left it for a week, drained the tank filled it back up with bp and went back to tuning.

plus i'm within a minute of a 24 hour bp.

[float_6969]

LOL, that certainly helps!

[rexhunta]

does for those wonderful egg and lettuce sandwiches on the way home at 4.30am