TunedRX300

I tried 89 on my RX300 and the MPG actually is lower. My RX300 manual says Lexus recommends 87 and "may" have better performance with higher octane gas. This means RX300 is tuned for 87 and may or may not get better performance with any gas > 87. I would stick with what Lexus' recommendations and certainly won't pay additional $ to get lower hp and shove extra unburned mixture down my exhaust system. Last, why would everyone believe 91/93 is a "premium" fuel when it is just higher octane, can you say marketing ploy?

looknow12

I always thought that higher octane burns cooler so you can squeeze more fuel mixture into the cylinder.

mikey00

I have owned 2 RXs now and use 87 in both. I found no advanatage whatsoever in using higher octanes, even a slight disadvantage in MPG. The FTC claims 6% of cars sold in US require premium, yet 20% of gas sales is preimum.

Campbell

Adding extra fuel without adding extra air will make your air/fuel mixture richer. That in turn will drop your cyclinder temperatures. Less fuel is a lean condition and cyclinder temperatures rise.
It isn't hard to add extra fuel to the cyclinder(Remapped ECU, bigger injectors, fuel pressure regulator) the hard part is adding extra air to the cyclinder so you can add extra fuel(turbo, supercharger, NOS, high flow intake and exhaust).
You basically decide on the air/fuel ratio of choice and match the fuel to the amount of air you can get in there.
Fuel in its self will not give more power by adding it to the current volume of air in the cyclinder, if you already have a good air/fuel ratio.

TunedRX300

Here is another helpful link to straight out what octane is. Again "premium" does not means higher performance. If you have an engine that is not designed for 91/93 octane, be careful, you may cause more harm and have less performance.

Octane FAQ

asic_bbc

Here is the article from USA today on the octane issue.
article

Ziggy09

ok... I'm not an engineer so I'm sure it messes up the engine... but I switched to 87 just to check it out.... The Results: 2.1mpg drop in fuel economy... but no drop in performance.

Lexmex

Since I admit to racing my RX at the track, I have a lot of experience with trying to squeeze in more air and perfomance out of my RX.

I use only 92 Octane Pemex Premium. I have regularly used Octane Boosters of all types (NOS, Prestone, Restore, etc.) and have never seen my MPG drop nor has my 1/4 miles time increased/decreased much, even with similar temperatures and keeping the engine cool (water spray).

Even then, because the engine is working harder at altitude, I still get 13.0 mpg. Don't laugh, my buddy with an LX470 down here gets less than 8.

looknow12

I think it might be coming back to me. Riding motorcross, we used to put high octane (+100) fuel in our bikes and change the fuel mixture to accomodate this.

TunedRX300

Also make sure mpg is calculate by dividing # of miles driven by # of gallons used, I find RX's computer is not accurate.

SigEpLaxer

With the prices in my area pretty high, I rolled back to the mid grade, which a guy recommended to me as he owed a RX300 like mine. With the 87 octane, it seemed to get less mpg, so I went up to the midgrade and hit the premium occassionally.

I've got the AWD 99 RX300 and I seem to get about 18 mpg across the board, highway and city.

MikeK

I too startted to rethink using mid-grade fuel instead of premium. Here in SLC, Chevron sells 85/88/91 octane fuel. I had used 88 octane exclusively in my 2001 RX300, however, I have been using only 91 octane in my 2004 RX330 (about the first 9000 miles). Guess what has happened? BETTER gas mileage (20.8 vs 19.7 on average) and no perceivable difference in performance during the last 1000 miles on the 88 octane gas. You bet I'm sticking with it!

Lexy GS430

No offense but, if premium is better for the injectors, then shouldn't that be a better reason to use premium fuel all the time? Just my thoughts on this matter.

HarrierAWD

You may need to let the engine adjusted to 87 before you get back the same mpg. Give it a few tanks and see what happens. I use 87 exclusively. Once I tried premium and didn't see performance or gas mileage gain, so I rolled back to 87.

My 2002 RX300 used to get 17 mpg in NYC. Now I get about 24.5 mpg on Colorado highway at 75 mph. Still use 87, which is mid-grade in Colorado.

Campbell

It is advertised by some brands that higher octane fuels have added detergents. Stating that they have "extra and/or special" detergents only available on their most expensive fuel. Maybe they do. I really don't know. They don't advertise when they are changing the blend during the change of the season. So I don't know what to believe from the petroleum giants.
I've also had some people tell me that using a bottle of STP injector cleaner works also. I've tried it and really haven't noticed any difference on cars that have 100,000+ miles on them. Still, every once in a while I throw a bottle in hoping maybe it is helping. Also, (I think I remember reading this) if you read the bottle it suggests adding it at every fill up. That adds approx. $5 a fill up. Not going to happen.
The only way I've ever seen a benefit and justification for an injector cleaning is with high flow competition injectors. This is when you send off all injectors, they get checked for operation and measured for flow. Then they are cleaned ultrasonically. Checked, remeasured and sent back with report. Kind of hardcore for a daily driven car.
As for clogged injectors, I tend to believe that unless:
1. The vehicle sits for extended periods of time,
2. You have a poor fuel filter,
3. You are running some crappy gas that likes to turn into varnish at the drop of a hat (Total speculation here),
you should not have any injector flow problems. Certainly not with a new 330 anyway.
If you feel the extra additives might help, for peace of mind go with the high octane. You bought a $40k car. Is 10-20c on the gallon going to hurt that much? Or maybe you can use a mid-grade and add an injector cleaner every month. Might be cheaper for you in the long run. There are probably bigger differences in additives between brands. Look-up and see who is the better for that. Just be aware that some brands come from the same big tank sitting at the port.
Personally, I think the decision should be based on octane alone. If we look at just this thread we see that an increasing number have had better results with a mid-grade. Low-grade has lacking performance and high grade a possible decrease in MPG however some increase in power via the butt-dyno. (I'd still like to meet someone that can feel a difference of 1-2 hp in a car. )
This is my own personal conclusion for the RX330:
Low-grade: some low rev hesitation, translation, lack of performance and lower MPG because the ECM might retard the timing to prevent knock. (I've never seen it but people here swear it happens to the 330)
Mid-grade: an all round good choice for the 330 as no timing retard, thus there is no knock. No reduction in performance and MPG that seem to excel the other grades.
High-grade: Decrease in power(very small) and lower MPG. However, a sense that you are feeling more power because you spent more money. And of course that wonderful thing called peace-of-mind. It is highly under-rated but should not be looked upon as a weakness or sign of stupidity. I love that feeling.
I still think 87 should be fine, but I'll never get to try it for multiple tanks as the wife insists on the premium