Why not meet in the middle, use 89 octane!

 

Costco doesn't sell mid-range.

 

You could pump half of each in to mix your own.

 

The most useless of the octanes, imo.

Run what the vehicle calls for.

If you want to ignore the requirements and "be cheap" then just be cheap and use 87.

89 is a no-mans-land of being not quite cheap enough but also not quite good enough.

 

This is not about being cheap(not wasting your money is not equal to being cheap) , it is a technical discussion that using 87 instead of 91 will hurt your engine (for real) or not.
many people do not care about losing 5 HP if using 87.
as I mentioned in my original post, many people use 87 on their BMW and Mercedes that requires 91 and have 0 engine issue.
the discussion is that if Lexus the same.

 

Some BMW's call for a minimum of 89 octane fuel.

I've seen older cars that call for 87 knock on that grade, but not on 89.

 

Today’s modern engines have sensors that adjust for lower octane. You might lose a few ponies but not enough to notice.

 

I have checked the user manual for 2024 RX and Highlander, as you see in the images below( taken from 2024 User Manuals left is RX, right is Highlander), both engines are identical even bore and stroke.
but then when I look at fuel type, RX requires min 91 but Highlander is 87.

so wondering why different fuel type when two engines are the same, is it because of possible different compression ratio like RX turbo pumps more air into engine so that 91 is required so fuel is not ignited premature?

Note: This is technical/mechanical discussion, so please refrain from posting advice etc

 

Highlander has 265 hp and 310 lb-ft of torque.
RX350 has 275 hp and 317 lb-ft of torque.

This tells me that the RX350 is optimized for 91 octane gasoline. I believe the optimization is on the software tuning, probably allowing some combination of more boost, more spark advance, and/or more aggressive cam timing to increase compression.

 

Although the rx350 is a turbocharged 4 cylinder, it will run without any issues with regular fuel.

 

Just a small complication in the issue is the difference in the RX models with Turbochargers. In this case I am assuming the tuning difference is to better match the electric motors.


Engine specs

 

I agree that is is merely software tuning. Both of these vehicles have the identical engine.

 

I believe that there is a typo in this chart. The RX350 FWD/AWD has the same 2.4L engine as the RX500h AWD, not a 2.5L as shown. 2,393 cm3 equals 2.4L.

 

Agreed. I never even noticed before. Wonder if Lexus has and doesn't care, or if they haven't found the error yet?

Click download PDF on the product specs line of the webpage.

 

Engines are correct but the chart is not showing the hybrid contribution to its horsepower and torque numbers.