SeismicGuy

Yes and do my calculation using the more likely 5000 miles per year and 40mpg and you will see essentially trivial extra expense for the premium.

midcow3

First , I am just trying to be factual and not trying to offend anyone with names or such.

Current Exxon gas prices at my local station : regular $2.48 , mid-range $ 3.00 , premium $3.50

Let's say you burn Premium and get 5% more mpg than regular. so if regular gets 39 mpg then premium would get 40.95
On a full 14.5 gallon tank regular would get 565.5 miles and would cost $35.96 or $ 0.0635 per mile
On a full 14,5 gallon tank premium would get 593.8 miles and would cost $50.75 or 0,0855 per mile

0,0855 / 0,0635 = 1.346 or 34% more

====================

okay better scenario lets say premium gets 5 mpg better. regular = 39 mpg , premium =44 mpgOn a full 14.5 gallon tank regular would get 565.5 miles and would cost $35.96 or $ 0.0635 per mile
On a full 14,5 gallon tank premium would get 638 miles and would cost $50.75 or 0,0795 per mile

0,0795 / 0,0635 = 1.252 or 25% more

===
either way 25% more or 34% more is significant.

I find it to be the ultimate oxymoron to by a high mpg car to get good gas mileage to have lower costs and then to buy more expensive fuel than is needed. If cost is irrelevant to you, then maybe you should have gotten a 350 instead of a 350h or maybe even something other than a Lexus that is more performance oriented ,such as a BMW

Peace to all. No offenses meant , unlike some posters. Take care and have a great day.

YMMV,
MidCow3

midcow3

Lexus NX 350h gas requirements

romer

To everyone viewing or participating in this thread--it was not and is not about what costs more, premium or regular (everyone knows one costs more--but where you buy your gas, what part of the country you're in, how many miles of that kind of driving, etc. etc. all affect you mpg--but I'm off topic!!!). Geeez. It has nothing to do with that issue. For people who have a fixation on the issue and can't let it go, let's all just say sincerely and deeply, peace to all. But please if you have a need to talk about the costs of gasoline--post it in another thread. The original question--recall--was why Lexus recommends Premium for the NX350h.

midcow3

As you can see Lexus gives a very clear answer to OP's question "for optimum engine performance" ( see yellow above). Then right after that Lexus's hedges big time talking about regular ".. in this case engine performance may be decreased. It does not even state with certainty that engine performance will be decreased. Nor are the sets of very wishy washy nebulous statements quantified anywhere.

Statements like these are added to prevent liability lawsuits and are basically meaningless.

LAST POST TO THIS THREAD - IT IS A DEAD HORSE


YMMV,
MidCow3

Lexicon1

Does anyone know what the ICE produces for horsepower for each of the manufacturers ? A poster above indicated they are not the exact engine as the stand alone ICE vehicle.
I have not been able to find what the hybrid ICE engine produces on its own aside from the electric motors which we know are different in each of the vehicles above.
IF the specs are the same for the ICE's, then one would also have to assume you would use the same octane fuel....
So, no one has answered why Lexus specifies Premium Fuel.....

43sbest

Bottom line-----------------------If you can afford to buy a Lexus you should be able to afford "Top Tier" 91 or 93 octane gas.

Droid13

There are slight differences in output specs for the same engine depending on the model and market of car they go into (including any subsequent model specific tuning adjustments), but generally the A25A-FKS engine (NX250 or RAV4 gas) is ~203HP and 184 lb-ft torque whereas the hybrid variant (A25A-FXS) ~188HP and 179 lb-ft torque (or less depending on market). Bore and stroke (and therefore displacement) as well as the rest of the block is generally the same, but the FKS (gas) variant has a static CR of 13 to 1 whereas the FXS (hybrid) variant has a static CR of 14 to 1. The difference in compression ratio is directly due to cylinder head design, but the FXS variant will also have different valve timing, after all that is really the modern definition of atkinson cycle engine, one that has a very wide range of potential valve timing. This very wide valve timing range is what makes it possible for these engines to discourage intake of air (the so called anti-turbo effect I mentioned that seemed to rile up the masses, relax, its just an analogy) for greater efficiency especially with light loads. Some gas only engines are starting to creep forward in the range of valve timing capability too to tap into this efficiency, to the point where the line between typical and atkinson engines is fading. The challenge though is that atkinson engines still sport higher CRs and that isn't so easy to dynamically change like valve timing. These engines take in less air / less fuel when cruising so they need the higher CR to keep the mid range power/torque decent, but under full throttle then you start to deal with a true very high compression situation as valve timing switches to permit maximum air intake which is where the premium comes in. If the engine is tuned to allow it, the engine will push the ignition timing to get a handful more HPs using premium. If the engine is not tuned for it, then the ignition timing only pushes the envelope as dictated by regular gas, premium does nothing. And in the case of the NX350h, the tuning is such that it can make a little extra power with premium but will keep the timing/power slightly back if regular gas is detected / knock occurs.

That said, why not put regular gas in every car that requires or recommends premium and just let the knock sensors adjust the timing. Not quite so simple, knock sensors are reactive to knock and will adjust timing when knock OCCURS. On an engine where actual CR can get high very quickly (such as high boost from a turbo) and/or the engine is tuned to expect premium to make max power, knock can onset too often for knock sensors to manage properly and damage could result. If the engine is tuned for both fuels (like the FXS variant hybrid engine), it will not be as aggressive to prevent damage. I mentioned before the difference in power output form the T24A engine in the NX350 and highlander. The highlander expects regular always so it isn't aggressive with timing while sacrificing a small amount of power doing so compared with the NX350, just like the NX350h can dynamically sacrifice of bit of power to use regular. Which is correct depends for you, and you alone, to make that choice.

Lexicon1

Droid, Excellent info and description and it prompted me to hunt for more info.
Assuming Wikipedia is accurate
For the Rav4 Hybrid, the Rav uses the A25F-FXS which has 176 HP and 163 lb-ft torque
For the Lexus NX350h, the Lexus uses the A25A-FXS which has 188 HP and 179 lb-ft torque (as stated in the Droid posting)

So, the Rav4 and the Lexus engines have a different engine designation and therefore are NOT identical , hence the difference in gasoline specification for the Lexus

I don't know if its purely a software change or there are mechanical changes

https://en.wikipedia.org/wiki/Toyota...c_Force_engine

Thanks Droid
Much appreciated

romer

The last two posts and the previous by Droid13 are what I was hoping for on this thread (actually you two gave even more than that!). Thank you

BabyLFA

I've had the 2022 NX450h for over a year and a half now, with almost 30k miles. I've used premium for about 6 months, and regular for about 6 months with road trip just to test the different, and see absolutely no different in MPG, it vary of course, but again I never race my NX to see the performance recommendation from lexus, I have my sport car for that, so since then I stay with 87 octane.

Oh, I've logged EVERY single fill ups since I got the car in a 3rd party app fuelio, not the lexus calculation on the dashboard, so I know exactly how much gas I've used and how much I've spent, and have yet to missed a log for a fill up. So if you like to race your NX450 go premium, if not and you just do normal driving, I really don't see why you would need premium gas.

One more thing RAV4 Prime is the exact same engine as the NX450, and it uses regular gas, RAV4 prime is faster than the NX450 from 0-60, and NX450 is tuned for better performance. RAV4 prime 5.5 sec, NX 6.0 sec. explain that

romer

Several detailed engine descriptions and analyses above indicate the 350h engine isn’t identical to the RAV4. But here’s the thing. MPG is not the only metric or consideration owners employ. Some people want to have the car perform at its best expectations. Some people care about the long term effects on the engine from using the less than recommended octane. Some people care more about mpg for planet earth than a few extra pennies in their piggy bank. The mpg issue is very difficult to unpack because it’s impossible to replicate the claims of any individual’s reports, despite their reported procedure and sincere though they may be. Bottom line take away for me in all this—paraphrasing Droid13–every owner gets to decide which octane to use. Regardless of manufacturer recommendations, real world behavioral results, etc. Individuals have different values. Some people value speed and performance. Others MPG. Others favor responsiveness. The variables are near endless. Decide for yourself. Enjoy. We’re not engaged in conversion activity here…it’s a forum. Not a religion. YMMV

BabyLFA

The 350h and Rav4 Hybrid both have the A25A-FXS 2.5L I4 gas engine, same as the new highlander and RX hybrid, so what's the difference between the 350h and the Rav4 hybrid engine, if you're saying it's not identical?

romer

This was posted on another thread. I’ve only used a portion of the explanation of the differences: There are slight differences in output specs for the same engine depending on the model and market of car they go into (including any subsequent model specific tuning adjustments), but generally the A25A-FKS engine (NX250 or RAV4 gas) is ~203HP and 184 lb-ft torque whereas the hybrid variant (A25A-FXS) ~188HP and 179 lb-ft torque (or less depending on market).

KennyFSU

Curb weight.

RAV4 ~ 3500 lbs.
NX 350H ~ 4080 lbs.