Thanks for this, interesting to see the actual ratios. Although I know the engine blocks are the same, I knew there needed to be some difference between Toyota and Lexus. I wonder if there is a difference between Honda and Acura because when I was loaned an MDX, running it on lower octane would show a difference.

You are right though, modern technology and knock sensors work well. Unless people have driven much older cars, I do not think many will really see what different octane ratings do to engines pre-modern tech.

Also, I have personally ruined a cat running 87 octane on my 4 cylinder (2AZ-FE) Highlander which I owned before my RX330. I blame it entirely on the fuel as there are some crappy suppliers around me. Have always kept up with maintenance on that car but never put good gas it, needed to be the worst and cheapest gas I could find. Car lived for 10 years and ~170K on the clock.

 

I have an acquaintance that is a Toyota Master Certified tech and I always defer to him for help with maintenance and he is really helpful. I asked him about this and he said "Some manuals will say "recommend premium" while others will "require". If its required, then you must run higher octane. This is usually because of compression ratio and more performance oriented rigs. There is a mechanical compression ratio which is the area above the piston at TDC vs BDC. Then there is what is called "effective cylinder pressure" which can take a mechanically high compression ratio and lower it by valve opening, overlap, duration etc. In most Toyota's built now, the engines have 11.5:1 compression ratio. This was huge, usually anything around 9.5:1 and up required premium fuel, but because of the VVTi, they usually lower the effective cylinder pressure. So regular grade gas is all that is needed."

Again, for those that want to run premium, I say go for it, I don't know how much "increased performance" you get from a 230hp motor driving a ~4000 pound vehicle, but it can't hurt that is for sure. At $.40 more per gallon at SAMs club, I just haven't seen the advantages for our RX330. To be fair, I have only tried a few tanks of premium, so the sample size is small, and yes I realize it is only about $240 more per year at 12,000 miles per year, For our situation, unless we are heading up in the mountains or something like that, I run 85. As always, YMMV.

 

I do believe 85 is fine to run, but my RX350 says premium so that's what I use and I don't mind paying a little extra for it. Engines die from wear, so the name of the game is minimizing contaminants. That's where following the service intervals come into play, filters, etc. Poor air filtration and gasoline can both be primary sources of contaminants. Once they are in your engine they create wear and a little at a time, metals from internal parts are also released and create more wear. Main bearings, crank, you name it. Tolerances are lost, valves begin to wear and then real problems can begin as small amounts of fuel are introduced where they shouldn't be, mix with oil and dilute it and its viscosity which can lead to other problems like overheating and gasket failures mixing coolant with oil, and so on. Fortunately for us, these are high quality engines that can take a ton of abuse and are engineered to adjust to lower grade fuel and filter contaminants well. That said, I will continue to follow maintenance schedules exactly or before and run the best gas I can find.
As for injector cleaner, most say that running 91 keeps things clean inside anyway. Less Methanol, varnish, etc.

 

One more reason to fill up with premium (from the 2005 Lexus RX330 Manual)....

 

I agree, I don't really care for performance or MPG, it's a luxury SUV not a sports car or hybrid. But, with such a great investment, I do not want heavy repairs down the road. The single cat on my HL was a tough bill to chew, I can't imagine changing two on the RX.

Good to hear you're getting good results from 85, definitely depends on regions too, I'd assume since you're closer to the southern states that produce lots of oil, your gas is much better then what is hauled all the way up north for me. I run 85 on my Toyo's, no issues but even the manual says 85 is fine unlike Lexus' recommended fuel.

 

Agreed, best to follow the recommendations from Lexus for your investment & curb the unnecessary repair expenses for ownership.
RXs also retain excellent resale value therefore should be regarded as a "great investment".