best octane fuel?

[hhgsm31]

Just curious if the type of gasoline we use matters? I know that higher octance normally = better, but my lancer says it shouldn't be ran on higher than 87 because they don't use the richer stuff in japan. Just curious as to what everyone runs

[aaronstj]

Run it on regular.  Higher octance does not mean better, that's a common misconception.  Some high performance engine are designed to use higher octane gas, and so in that case, high does mean better (to a point), but not the GS500, which would probably run just as well on potato vodka.  Just use regular and save yourself a dime.

[makenzie71]

a higher octane rating doesn't mean it's better...it means it's a higher octane.

Run as low an octane rating as you can without knocking.

[AWD OWNZ U]

Just curious if the type of gasoline we use matters? I know that higher octance normally = better, but my lancer says it shouldn't be ran on higher than 87 because they don't use the richer stuff in japan. Just curious as to what everyone runs

The gas in Japan is similar octane to what we get, they just measure in RON. Octane is just a measure of combustability, which translates into resistance to knock for motors. Like the guy above said, unless you are knocking generally you are fine with 87.

[skoebl]

In some cars (like the Scion tC) running a higher octane fuel is just money down the poop-chute, and could possibly increase wear and decrease reliability over time.
Although, it is true that some cars will run better with higher octane fuels. My '90 Mustang 5.0 ran really well and got about 26 mpg on 'premium'. My little '91 Escort ran a whole lot smoother and got better mileage as well. So it's really just a case by case thing.

Just repeating what's already been mentioned, octane is a fuel's resistance to combustion. So a higher octane rating means it will combust at a different time than a lower octane (or will require a more powerful spark...there are probably lots of variables that contribute to how it works).


*Edit* Oh yeah...and in vehicles with forced induction, you must run a higher octane fuel because the pressure is higher. If you were to run a low octane in a vehicle with forced induction, you would get pre-ignition (which I think is what a "knock" is...as opposed to a 'ping'  someone correct me lol), and have a very inefficient system.

[GSinUS]

I've been running on 91 all this time just because the Hayes manual says it's the minimum recommended fuel grade.  But this post made me go back and recheck.  Turns out it's 91 using the RON rating (used in Europe?), which I believe is the 87 here.  Next time will save myself some $ 

[Egaeus]

It pretty much goes like this. 

The higher the octane content of the fuel, the higher the temperature that is needed to get it to spontaneously combust. 

The higher the compression of your engine, the hotter it heats the fuel. 

If you put low octane fuel in a high-compression engine (turbocharged and supercharged too), it's going to combust before the piston reaches the top of it's stroke.  This will beat the hell out of your expensive engine. 

If you put high octane fuel in a low-compression engine, you're just wasting your money, because it doesn't heat low octane fuel to the point that it's going to combust unless it's running very hot for some reason, which you need to fix for obvious reasons.

The GS500 is a relatively low-compression engine, so it doesn't really need the high octane fuel.