dibl

The VVT-iW can effectively reduce the compression ratio, a quasi-Atkinson cycle effect. If the ECU can control the VVT-iW and the ignition timing simultaneously, not to mention the fuel-air ratio via the EFI, then you have a range of compression and ignition combinations to dynamically adapt to the actual ignition behavior of the engine with whatever fuel it is using.

plee82

Great. The dealer filed my tank (assuming 87 regular). Drove it until half the tank and then went to Costco over the weekend to fill it with 93. Costco in MA only has 87 and 93. 20 cents difference only. Drove 200 miles to NH, got around 24MPG. Not bad.

dibl

I've seen 27 mpg. on a long trip with mostly cruise control, and 70 mph.

plee82

I am sure. I did not use cruise control because it's a new car, trying to vary the RPM a bit

dibl

Exactly correct. I did that, and changed out the oil at 1000 miles. I don't go for the 10k miles changes. My normal day has at least 6 starts and stops of the engine, and not a lot of miles traveled, so it's hard on the oil and I change it at 5k miles.

1Louder

I read a C&D article on this a year ago or so that did a pretty interesting experiment. They drove several different kinds of cars requiring different kinds of fuels to see if using less than what the car recommended made a difference.

Very bottom line, the dyno results showed small drops in hp (like 1-5) using lower octane fuel in a car that recommends higher. None of the drivers said they could feel any difference in "butt feel" driving the car. So there is likely a small difference, but maybe not one that you may notice. My recommendation would be to try a tank on each and see what you conclude. Each of the cars C&D tested had slightly different results.

MPG results varied too, some getting 1-2 MPG lower with the lower than recommended Octane. But some cars did equally well.

plee82

I'm on my third fill, using Costco 93 (they only have 87 and 93, 20 cents difference). The acceleration is much better imo. The first thing I noticed about this car initially was that the acceleration was bad, very bad compared to my Acura MDX 2020. Now, It has improved a lot with the premium gas, but still not close to my MDX 2020. I will just keep filling the car with 93 octane just for the performance. Alternating between both cars, I can appreciate the pros and cons of both the Lexus and Acura.

dibl

If you think any of the acceleration issue is due to the pedal responsiveness, there's a device called a "Pedal Commander" that changes that. It's not cheap, but it does give you total control over the responsiveness to a push of the pedal.

sderman

Might be the placebo effect. Have a friend fill your empty tank with either 87 or 93 without telling you which and drive until empty. Then have that person fill your next tank with the other fuel grade and drive until empty. After driving both tanks compare your blinded experience with your friend's fuel details.

Quantum501

That is the way to do it. It is how we taste wine to avoid the inherent bias.

dibl

Yikes -- please don't do that, or even close to it! You'll burn up the fuel pump! Even with a gallon or two, when you turn a corner it all sloshes to one side, potentially exposing the fuel pump to loss of cooling (and your wallet to a major leak ...).

Double-blind experiments are fine, when feasible. But objective data can be obtained from the odometer, the numbers on the gas pump, and a calculator, as I posted above.

Quantum501

yeah....didn't notice that drive until empty part. Good catch

websurfer

I just got my RX less than 2 weeks and I tested both at 89 and 91 also. I found 91 (not 93 in our area) gives it a tab more power. Then again, I'm don't drive the RX as a sports car. It's good enough for us.

lesz

While the variable valve timing used in modern car engines should be able to adjust to different grades of fuel, my understanding is that the adjustment is not instantaneous and that it takes some time for the adjustment to complete itself. So, I believe that, in order to be able to do a meaningful comparison, you would need to consecutively use 3 or 4 tankfuls of fuel with each grade before you would be able to see any difference in power or mpg caused by the change in fuel grade.

In any case, you might well find some minor differences in both power and fuel efficiency, depending on the fuel grade, but those differences should be minor, and using the lower octane grade will not harm the engine.

lesz

Yes, plee82 has likely experienced some sort of placebo effect or, perhaps, a confirmation bias. As explained in the previous post, if there are any (minor) power improvements or mpg gains resulting from using the higher octane fuel, it would take the car's variable valve timing multiple tanks of the higher octane fuel before any adjustments were completed and any (minor) improvements would become apparent.