Actually, it's the same as our 93 octane. They use R.O.N. - Research Octane Number. We use A.K.I. - Anti Knock Index, which is the average of R.O.N. and M.O.N. Motor Octane Number. MON is tested with a different protocol, but the results are typically 10 points below R.O.N. So 98+88/2 =93

 

Not exactly.... well, AKI= RON+MON/2, but "typically" isn't exactly... I commonly seen MON described as "roughly 8-10 points lower) but sometimes it's more or less...For example, Shell in Australia states their 98 is actually 98 RON but only 85 MON-
http://www.e90post.com/forums/showthread.php?t=60433

That'd make it 91.5 (still fine for a 2IS of course)

And here's fuel on a sprint cup car with a 12 point RON/MON gap-
http://www.ask.com/questions-about/S...Specifications

most numbers I've seen on AUS fuel though look more like in this chart-
http://jeepgarage.org/archive/index.php/t-24598.html

Putting 93 at 97.4 and 94 at 98.5... thus saying 98=93.5 is about as roughly right as most answers.

 

Again, your 98 is not the same as 98 in the US. It'd be roughly 93.5 in the US.

Almost nobody outside of the US uses the US AKI system for octane rating... most countries use RON (including everybody I know of in the middle east).

The only benefit, ever, to higher octane is resistance to knock.

If your car NEVER knocks on 91/95 you'll get nothing from running higher.

Anything above 91 (which is roughly 95.3 in the middle east standard) will not benefit the car in normal conditions... (now, racing across the desert in 110 degree weather might get you into knock territory even on 91/95, so you might get some benefit of 93/98 that way...but that's a bit of an edge case for most drivers)

 

Just as right, and just as wrong. I'm not sure what makes an anonymous poster at jeepgarage.org your ultimate authority.

I've come across numerous references stating that 98 RON is equivalent to our 93, including this book, "Characteristics of Petroleum Products for Energy Use", where they define SuperPlus as 98 RON, 88 MON:

http://books.google.com/books?id=9rq...page&q&f=false

And I've found product sheets for 98 RON where the MON is lower than 88 (98 RON = 91.5 AKI), such as Dutch Gulf:

http://www.gulf.nl/fileadmin/user_up...8_unleaded.pdf

But not a single product sheet for 98 RON gas that has a MON above 88.

Of course, I'm sure you'll say that both of those references are European, not Australian.

Well, here is an Australian government document, where they define premium unleaded as 95 RON, 85 MON, the same 10 point spread that I quoted.

http://www.accc.gov.au/content/item....hapter%207.pdf

I believe it is perfectly correct to say that 98 RON gas is nominally the same as our 93.

 

I can list 50 other sources that all agree with me if you'd like....

http://en.wikipedia.org/wiki/Octane_rating

Note the only 98s listed described as "93-94" AKI


http://www.m3post.com/forums/showthread.php?t=355408
http://www.cadillacforums.com/forums.../t-208221.html
http://www.bimmernut.com/forum/5-ser...tml#post156812
This one is from a guy in Australia even!
Can't quote, as it's a chart from an article... but it lists a specific fuel as 98 RON and 90 MON....which is... 94 AKI.

http://www.fjowners.com/index.php?topic=3255.10;imode
http://townhall-talk.edmunds.com/dir...ew/.f0a7425/56
Seriously how many more do I need? It's not like I found ONE random dude on the internet saying this and believed it.


Yup...15 yr old book, and it's discussing one specific blend fairly recently introduced to France at the time.

That, and you've only shown one product sheet at all...



Uh, no, it does not define it as that.

Let me quote you your own source

They're not exactly 95 and 85. They're at least 95 and 85.

In other words your source says nothing at all about there being a 10 point spread other than that would happen to be the spread if it met the bare minimum in both categories. 95 RON and 87 MON would meet the spec too for example.

Also meeting the spec? The 98 RON and 90 MON fuel in the article that Australian guy posted a copy of. Which again works to 94 AKI.






and I don't.

We're allowed to disagree.

I just find a lot more folks out there agreeing with it being a range of numbers, not exactly 93.

In fact, your own sources do too (since you quoted one source showing a 98 RON fuel being equal to 91.5 AKI)

In either case in any example 98 RON works out to higher than 91 AKI, which is what the 2IS requires.

 

Thanks a lot Kurtz. Never knew US had a different octane rating system. That is why I used to always wonder how come we don't get 93 and 91 here , hehehe.

Anyways now I'm better educated with the system.

Ok so a final question, Will my car accelerate much better and feel more powerful when I use 93 / 98 octane , or is it just a placebo ?

 

Under normal driving conditions you should notice no difference between using 91 (US AKI octane)/95 (middle east and most other places RON octane) and using 93/98.... because the car should never knock with either.

It's possible under very severe use (I dunno, yanking a trailer along in 110 desert conditions or something with the car floored) you might manage to get knock with 91/95 in which case 93/98 would be a benefit... but not otherwise.

Once you're running a high enough octane to prevent knock you get nothing from going any higher (and that's 91/95 on a 2IS in normal conditions). The only thing octane is a measure of is resistance to knock.

 

Good stuff......

 

I don't know about our cars, because I never tried putting lower than 93 into my IS, but in my previous vehicle even though premium is not required i could feel a noticeable difference when accelerating between 87 and 93. It was a honda civic btw.

 

felt, or proved on a dyno/track?

Because if the manual spec'ed 87 it was only the first one. (I think the SI civic needed higher for at least some of its run, but not the regular civic)

It's impossible for the car to be any faster on a higher octane fuel than is needed to make it not knock.

Anti-knock is the only thing "more octane" gives you.

(now, if there was something wrong with the previous vehicle, you might be on to something, but not running properly if it was programmed for 87 from Honda)

 

Yes, only Si model requires premium. And I had just an Lx for which regular is just fine.
I did not say it became faster and I doubt it did. I am just saying how did it feel, and there was a noticeable difference, when accelerating (4-5k rpm). Acceleration felt smoother.
My friend has his 2nd civic now and on both cars he could feel the difference as well, so it is not just me.
With IS it might be no difference at all, i do not know because i did not try lower than 93 octane and i am not going to.

Just sharing my personal experience.

 

I have to agree with polo8 on this. There definitely is a difference while driving on different fuels.On 98 / 93 octane It feels butter smooth while accelerating. I do not know yet if my mileage has improved as I'm still on half tank and might need another week to empty it and refuel with my previous 95 / 91 octane to know the actual mileage and acceleration feel.

So far the fuel mileage is also more or less the same. Thought the temptation to floor the pedal is higher on the 98 / 93 fuel. Maybe it's just a placebo. But there definitely is a difference in the way the engine responds or feels.

For instance the difference in quality of fuels is easily seen in older engines like my friends 99 Honda accord coupe. On very hot summers his engine struggles with the air con on with 91 / 87 octane fuel. But with 98 / 93 octane , his engine feels much smoother and better according to him. He is using 93 for now as it is summer time here.

 

On old motors the compression ratio supposedly can effectively get higher as more crap builds up in the cylinders, so they'll start to knock on the same fuel they ran fine on when brand new.... not something I've experienced myself though.

But I'm telling you, "octane" doesn't do anything other than resist knock. That's literally what the measurement means.

So it's simply not possible for running a higher octane fuel than needed to avoid knock "helps" in any way.

It's be like saying wearing platform shoes helped your hair regrow.

Now, if the engine had other problems that was causing it to knock on the fuel it was designed for, it'll run "better" on higher octane because it'll stop the knocking problem.

the best solution is to fix what's wrong with the car though, not band-aid it with fuel. It's like folks who "fix" an oil leak by running thicker oil instead of actually fixing the leak.

(the other exception would be like I said if you're driving it under severe duty conditions where it might knock even new on it's normal fuel, but they'd need to be pretty severe on an otherwise properly running car)

 

87 is perfectly fine! 87 octane will not make your engine knock. These engines do not know whether you have 87 89 or 93. The o2 sensor heats up and that helps regulate the fuel mapping somewhat to steichometric.

I have raced against my buddies is250 that runs 93 octane, and I beat him. My mpg is about avg as the rest of the is250. So I dont know what your theory is that it is not ok to run 87 in a is250.

Is350 I would run 93 octane only, because that generates more power = more heat = more prone to pinging or knocking.

 

You seem to be somewhat confused on how cars work and what octane is.


Octane is a direct measure of a fuels resistance to knock. That's the definition of it.

Your car is programmed to run on 91 octane. The engine timing is advanced to run on that fuel. That is, the stock timing maps require that level of knock resistance to insure the engine won't knock.

If you run 87 then yes, it can, and will, knock under those conditions.

You won't notice it because the knock sensors are very quick, but it will knock.


Your O2 sensors do not change the cars timing, that's not their function and not within their capabilities.

O2 sensors will adjust how lean or rich your fuel is, not the engine timing. Further, much like knock sensors, they are making adjustments AFTER the fact (ie they notice the last burn was lean, so they add fuel).

O2 sensors react to being too rich or lean and adjust fuel amounts accordingly.

KNOCK sensors react to the engine knocking (which your car will do on 87) and reduce engine timing from what it's programmed for from the factory, this reduces performance, efficiency, and BTW, your engine is now damaged (very very very slightly)

While running lean is one thing that can contribute to knock (again, only noticed AFTER it has happened) it's by no means the only one.. so O2 sensors don't "eliminate" or prevent knock at all.

Things that contribute to knock that the O2 sensors have nothing to do with:

Compression ratio and combustion chamber design (you can't really do much about these other than recognize you're driving a car with 12:1 compression)

Spark advance/timing- You can't do anything about this either- other than recognize this is programmed for 91 octane from the factory. The knock sensors will pull it back (temporarily) after it detects knock. The fix is higher (correct) octane fuel.

How aggressively you drive, altitude, humidity, air temp, and- fairly important to the 250- carbon buildup in the combustion chamber.




Which tells us exactly nothing.

I could list a dozen reasons that exactly identical cars would win or lose a race against each other having nothing to do with fuel or engine timing.

Unless you were hooked up to the OBD-2 port datalogging you can't state how well the car is actually running on the fuel, only how well you THINK it is.

Notice that 0 of the people who insist "my car doesn't knock on low octane fuel!" have ever provided any data to support the claim.

(if you WERE datalogging, by all means post the logs please)


The 250 actually runs a slightly higher compression ratio than the 350 FYI... regardless, since both are programmed for 91, running higher than 91 won't help you (unless you're racing in fairly abusive conditions like 110 degree weather for hours at a time or something)