Originally Posted by AZ JB

Goshhhhh Luckyyyyyyyyyyy...

Originally Posted by S to the K

Here in the DFW area, 99% of Super Unleaded is 93 octane?

I wonder why some other states get the shaft with mainly 91?

Originally Posted by Kurtz

It's often an altitude thing... but nobody's really getting the "shaft" unless their car requires higher than 91.

Which the 2IS does not.

93 does nothing helpful if your car is programmed for 91.

Originally Posted by rob stolen

I disagree.

I recently did testings with full tanks of both octanes at multiple different stations/times (probably 3 or 4 each) just to see for myself if there really was a real difference and I DID notice that 93 octane ran smoother than 91, especially at idle. 90 octane was even worse. And no, I did not go to any no name gas stations at any point in my testing.

However, I did NOT notice any real performance difference between any of the octanes, just a smoother idle & engine.

Where does it actually say in the specs from Lexus that the 2IS is a 91 octane specific engine? Really? I would like to see that.

I do know that a car requiring regular unleaded (87 ish octane) will see no benefit from 93 octane, and may actually cause damage to the engine with consistent high octane usage. However on the IS, I think a higher octane super unleaded gas does reap some benefits. That's what I experienced.

And anyways, if one station has 91 & another has 93 for the same, everyone would choose 93 as a no brainer. Why not?

I guess if you live in an area that doesn't have any 93 octane stations, then you are getting the "shaft!"

Originally Posted by AZ JB

Kurtz are you suggesting that anything with a higher octane than "super unleaded" is not beneficial for our cars??

Originally Posted by Kurtz

Numbers don't lie... conclusions drawn from them can be drastically wrong though. Like a guy who resets his ECU when he installs an intake and is SURE the difference in how the car drives right after is from the intake, and can show you numbers. But the change is really from the ECU reset, the intake did almost nothing.


It's simply impossible for "brand of gas" that is otherwise the same (octane, ethanol, driven in the same car under the same traffic and driving and road conditions, in the same weather) can produce 20-30% differences in mileage.


There's lots of variables that CAN cause significant mileage differences other than brand of gas though, that I suspect your numbers don't honestly control for.

Go talk to an engineer that actually does this for a living sometime (smpis350 has done so and posted about it)... he'll laugh at you if you try and "scientifically" claim the brand of gas changed your mileage like that.

Gasoline is fungible. In part this means that the base fuel is the same from one brand to another. The differences that are added afterward simply can not make significantly changes to mileage from one tank of gas to another.

Now...drive the car aggressively, in traffic, in certain weather conditions, on certain roads, using a fuel blended with ethanol.... then drive the car passively, without traffic, on different roads, in different weather, using a fuel without ethanol, and you can see drastic mileage changes. None of those things reflects the brand of fuel though.


AFAIK there's no brand that universally avoids ethanol year-round though (but you might find a certain station that doesn't have it in your area)... part of the reason is what was stated, tankers delivering to stations draw fuel from the same sources, and then just put in the brand-specific additive package (which can, in no way, have the sort of impact on mileage folks are claiming).

Originally Posted by Kurtz

I'm not "suggesting" it, I'm stating it as a fact.

The car is programmed for 91 octane fuel. That's the timing it runs. If it detects knock it pulls timing, but it never adds any more than it was programmed for.

Anything higher is completely useless under normal circumstances.


Now, for a forced induction application that's another story since you're going to have no control over engine timing so increased knock resistance can save you from a blown motor. Higher octane, in and of itself, won't, ever, add any power though, because it's not possible for it to do so.

In the case of the poster I was replying to he suggested that 93 somehow produced a better _idle_ than 91 though, which makes even less sense since the car isn't really doing much at idle.