clubfoot

Your second statement is flawed based on your first statement! Of course timing advance is built into our ECU otherwise once you put in 87 it would retard the timing based on knock sensor information and when you changed back to 91, it will still think it was running 87! It will advance the timing again until the "onset" of detonation when you put back in 91!

The question should be "how much timing advancement is built into the ECU to take advantage of higher octane fuel?" 91 octane is the zero point because that is what Lexus used to develop the engine. Sure you can use 87, but that is below the zero point and NOT RECOMMENDED buy Lexus, same with 94 which is above the zero point.

Are you absolutely, 100% certain that our ECU would not advance timing to take advantage of 94?

neova

My statements make sense if you read them in context. The ECU will only advance timing back to match the 91 Octane fuel that it was designed to run on. Lexus will not design the ECU to advance timing beyond that is required for a combustion of a 91 octane gasoline.

I think most people misunderstand the relationship between octane and performance.You get more horsepower from a higher compression ratio, and a higher compression ratio requires higher gasoline octane rating to prevent knocking. So just putting in higher octane (without tuning the ECU to advance timing) will not result in higher hp output.

some good read (amongst many other articles on the net about this subject) http://www.wanderings.net/books/is-h...orth-the-money

neova

Hi LexusNut13

I think the topic of this discussion is about whether certain brands of gasoline and using a higher octane rating above 91 would give better performance. I do not doubt that you did in fact experienced eggsmell from your car after using Esso, but this has no direct relationship to whether Sunoco gasoline provides better performance over ESSO or other brands.

clubfoot

For those people who misunderstand the relationship you're probably right, but not I. You also realize that just advancing the timing does not guarantee more hp!? My point is that Lexus developed the engine for the North American market with 91 octane as the worst case since this should be the lowest "premium" available. But, they also know full well that in some states and Canada, 94 octane is also available. With all the labels and warnings they certainly don't expect anyone purchasing an IS350 to cheap out and use regular 87 in a "high performance" car! But I'm sure there is tolerance for 87 built into the ECU for "mistakes".
Any well designed ECU worth its transistors should take full advantage of all its sensors to extract max performance from the engine.

neova

Did I say that? I belive I said higher compression ratio, not advanced timing.

Octane ratings are variable according to altitude as effective octane ratings decrease when you move higher into thinner air. That is one of the reasons why gas stations needs to offer higher than 91 in some high altitude places in order to compensate for the loss in effective octane rating (such as 92 or 93 when up in the Rockies).


That, my friend, is the million dollar question. I am not convinced Lexus engineers would design their ECU to be able to perform beyond what is the designed combustion ratio. Maybe someone who worked at Lexus can chime in here?

clubfoot

OK, still not picking on anything you're saying but:
<<So just putting in higher octane (without tuning the ECU to advance timing) will not result in higher hp output.>> That (without tuning the ECU to advance timing) statement just came across badly.

OK, but I live in Toronto Canada, it's practically as flat as a pan cake here and we have Sunoco 94 octane, go figure.

neova

True, our cars don't need 94 in toronto given its (lack of) altitude. But there are high performance cars out there that are actually designed to run on OCT 93 gasoline minimum, so the Sunoco 94 is for them. For the rest of us, Sunonco has no problem selling the 94 since there are enough drivers who wants to pump it into their cars anyways, so if Sunoco can sell it, the will offer it.

AndyL

Just caught this thread and would like to throw my 2 cents.

I have been exclusively using Sunoco 94 because of one sole reason --- it is the only one that I could find in GTA that claims it is MMT-free and our driver's manual (I am pretty sure it is mentioned in other car manufacturers' manuals as well but in different wordings)

http://www.canadiandriver.com/articles/jk/040310.htm

clubfoot

Yep, that too and the fact that my son's JDM ST185 engine computer refuses to run without missfire on any other gasoline we've tried

zazzn

there are only a few cars that have a tune for high octane like the z06 i believe the requirements are 94 octane and if it gets 91 the computer retards the timing back which is why its rated less in cali.

However, I do think that if you run 94 you engine will knock less which will advance the timing to it's maximum.. this is especially true with todays high compression engines....

As for people saying they get more milage on 94 ... they are stupid and speculating. You need to burn 30% more alcohol to achieve the same BTU's of gas meaning you get less for the money.

However, when you are talking about power wise because of the higher octane on a boosted car you need the higher octane to fight pre-ignition / detonation... So it will give you more power but use more of the fuel to do that.

So in short 94 gives LESS milage then regular 91

clubfoot

Correct, this has nothing to do with fuel economy. The JDM version of the engine and computer we installed is tuned for higher than 91 octane, the engine ran just fine with the stock ST165 computer but every time we hooked up the JDM computer the engine would miss fire and the knock sensor would throw a code. Sunoco 94 solved the problem plus giving the engine more power.