100 Octane gas

[Midias]

^^^Yeah, but if the ECU changes the timing doesn't it have to change the air-fuel mixture also? If the ECU is always trying to attain optimal efficiency I can't see it adding the same air-fuel stoichiometry for different octanes, brands and winter-blends. As far as better engine performance goes I still do not personally feel/see any noticeable difference in performance between 87 octane and 93 octane (I'm stock) in my Solara. I'm not speaking for others but I feel the performance jump is only a tenth of a percent on paper but exponentially huge in my wallet. (I support unwed mothers, ya know!)

No it does not change The A/f mixture it still draws in the same amount of air and fuel but it changes the point in which the spark is set off.

[Gadgetjq]

Anyone ever run the 100 octane gas or use octane booster? I normally fill up with 93 octane and the car runs better on it. How would it run on 100?

There seems to be a lot of misunderstanding of what octane rating is. At its most basic the higher the octane the more resistant it is to ignition. Higher compression, flakes of carbon, deposits on valves and other factors can cause lower octane fuels to pre-ignite causing severe engine damage. Higher octane fuel isn't more powerful, doesn't burn hotter. In an engine not designed for it higher octane can actually reduce power output because it (effectively) retards timing (doesn't ignite as raadily as lower octane fuel). You can also end up with more combustion chamber deposits in the form of carbon.

The reason your Solara engine runs better on 93 octane than on 87 is because it's designed to run on 93 (note the 'use premium fuel' notice in your owners manual and fuel door). If you use 87 octane and 'if' it causes spark knock the ECU retards timing to account for it. Toss in a tank of premium and timing is slowly advanced again providing the power and fuel economy the engine was designed to produce.

Be careful comparing octane ratings among countries. In the U.S. octane rating at pumps is research octane + motor octane /2 . It's on the yellow sticker on every gas pump. In some countries just motor or research octane might be used, other countries have different formulas.

Cheers

[youngblood]

My feelings about octane selection are mostly derived from my experience with marine engines.

Boat fuel systems are very vulnerable to water contamination due to their operation in wet environments as well as the infrequency of their use. (water accumulates in fuel over time, so any gas left in the tank during storage has lots of time to absorb moisture before the tank is filled and the boat is taken out again)

Moisture in fuel is obviously bad for two reasons:
1. It causes corrosion and deterioration of fuel system components
and
2. It contaminates the gas and lowers its octane (amongst other things)

The recommendation is then to use a higher octane fuel in the boat so that even if it is contaminated and the octane is subsequently reduced, it should still be sufficient to run the engine without pinging or other problems. Specifically, mid-grade preferred because premium typically uses a higher ratio of ethanol(?) to achieve its octane rating. Ethanol causes it's own problems by being extremely prone to water absorbtion.

I run mid-grade in my lara for the above reason and not for any performance advantage. My concern over moisture in my car isn't due to the same reasons as the boat. It is the Michigan climate with it's wildly changing temperatures (which create lots of condensation in the tank).

I want the car to always have acceptable quality (octane) fuel without the negative aspect of the premium (ethanol).

Phew!

[Taido]

What about using 89 octane in the 2AZ? I felt a power increase from 87 octane but is it cleaner? Charleston, SC does get pretty hot and humid so there is the water absorption to worry about.

[gnegroni]

What about using 89 octane in the 2AZ? I felt a power increase from 87 octane but is it cleaner? Charleston, SC does get pretty hot and humid so there is the water absorption to worry about.

Perfectly timed. I was about to post then I read your input

I was feeling uncomfortable in my Solara because of increased frequency of pinging as the miles have piled up (65k and all hard driven). Two weeks ago I decided to complete 1/2 tank of 87 (running straight 87 for more than a 1 1/2 years now) the other half of the tank with 90 octane ( roughly octane rating of 88.5 (US).

In the end, I was pleased with the results, as of pinging had gone down to where I could barely detect it. However, my @ss dyno was making me believe I was not gaining power but felt more sluggish (read bog). Maybe if I let the ECU settle (or clear it), @ss dyno readings would be higher but simply forgot about it (4h sleep per day x month screws with you).

As for the weather effects, I live in Puerto Rico and its pretty hot and humid year round. While having bad weather, at 7am its about 80° with 90% humidity. It gets a lot hotter during day and fair weather, but humidity stays high all the time. Mornings make my car condese all over all year long. I don't doubt water condensation in fuel system could be having an adverse effect on our cars, but to what measure? Could we perform a little experiment and find out how much water goes into system? Could we weight-in the changes in a small tank of gas?

PS Even thought I've always used top tier gas with additives, what would be the best way to clean up car (SeaFoamed intake already)?