No, No, No!!!! What I meant about BS was someone's sales person saying "if you can't afford premium gas, you can't afford a Lexus". I'm 100% in agreement about what you said!!!

 

HaHa no worries. And yes I call BS to what the salesperson said!

 

I find it puzzling that Lexus recommends premium gas for the A25-a FXS engine used in the NX 350h - primarily because that same engine is used in so many other applications where Toyota specifically states that 87 octane is just fine (RAV4 hybrid, Crown, etc.) Granted (and according to wiki) the engine in the NX 350h is tuned to deliver a little more horsepower (4-12) than those other applications, but Toyota needs 4 more octane points to get there?!
If interested you can go to: https://en.wikipedia.org/wiki/Toyota_Dynamic_Force_engine
(Scroll all the way down to A25-A FXS) Maybe I'm missing something.

 

The 'pinging' that you hear is the pistons and cylinder walls and head ringing like a bell that was hit with a hammer because the low octane gas did not ignite and burn in a smooth pattern across the combustion chamber but the fuel mixture ignited all at once, in a explosive event.

This pinging or instant explosion of the fuel mixture is what causes engine damage.

Ping sensors are reactive not proactive, the pinging, or damage, has already begun before the ping sensor reacts and retards the timing.

Speeding the pinging event up to the extreme:
In a fuel dragster, spark plugs, pistons, valves are all destroyed in the last 1/8 mile of its run, the engine is running purely on detonation or ping.Thats why they overhaul the complete engine between races.

By using lower octane gas than recommended you are doing the same thing but at a much slower rate.

Your car, your choice.

Peace.

 

I don't think there's too much confusion there. It's the same engine, but tuned differently. There are different engine mappings for all kinds of variables, octane is just one of them. It's not unusual for "performance" versions of the same engine to include mappings that grant slightly higher performance when conditions allow(high octane premium), and reduce it to a "nominal" level when not (minmal octane regular), and a "survival" mode when unusual conditions occur (knock sensor detection). So long as you stay out of "survival" mode, using the minimal octane is fine.

Turbo engines have always been more sensitive to knock, so their requiring higher octane as a minimum is also pretty inline.

 

Interesting and thank you for your input. My NX 350h hasn't arrived yet but until there is something definitive on 87 vs 91 octane I plan on hedging my bet. I'll do the same thing I do with my wife's 2013 Audi A4 where 91 octane is also recommended and that is: blend equal parts 87 octane and 93 octane (the common premium rating in my neck of the woods) of Shell gasoline to obtain a blended octane rating of 90 and call it good. Yes, it's kind of a hassle but with the hybrid I'll be filling up less often. Meanwhile, the Audi has 115,000 miles on it, still runs great and has required very little maintenance. I don't want to mess with that success!

 

ECUs are computers and most have "active Learning". Initially it is detection and then topically the ECU learns m assuming you continue to use lower grade and the damage form pinging is therefore more minimized that just intial detection. Race Cares are a whole different animal; kind of like the trite saying "comparing apples to oranges"

IMHO , obviously some people do not agree, you could run regular ( Octane 87 ) in a turbo 350 NX and be just fine for a lot miles and the life of the car.

YMMV,
MidCow3

 

Just as an additional bit.....if you have an OBD reader, watch the ignition timing to tell if you need to run higher octane fuel. Advanced timing (positive degrees of advance) is usually an indicator the engine is running well, retarded timing (negative degrees) is when the engine is tryign to protect itself from knock.

That said I haven't tried it with our Atkinson cycle engines yet, not sure what "normal" looks like or if it would report any differently.

 

Atkinson engines (today anyway, those crazy diagrams of the original Atkinson cycle engines have little similarity) simply use extremely wide variable valve timing along with very high cylinder static compression. The really wide valve timing allows the engine to take in and burn a less dense air-fuel mixture but then is able to utilize the very high static compression to still get some decent power out of it (greatly increasing the efficiency with a modest sacrifice of engine HP and torque). When the gas pedal is stuffed to the mat and the engine is gulping all the air it can get, that's when potential knock rears its ugly head because of the very high static CR (much higher than NX250 or NX350-although the NX350 will experience higher dynamic compression due to turbo). The ignition timing itself will typically change normally as needed depending on power request and rpm.

It would be interesting to compare the ignition timing of a 350h at full throttle at say 5000rpm with regular vs premium.

 

i think it’d be more interesting at medium-high load at low RPMs, like 2000-3000. Full throttle is usually open loop mode, engine just follows a static mapping for “max power” and tends to be conservative with timing no matter what. cruising speed at low throttle with high load is when most knocking occurs. Harder to consistently replicate tho.

 

All data would be interesting data for sure! Yea, I've heard that some cars experience worse at lower RPMs, but from my own personal experience with my RX hybrid with the Atkinson 2GR engine I was always able to tell a substantial difference between premium and regular fuel at full throttle. In all other situations, I could not tell any difference. Now that engine was technically a "premium required" engine, not a "premium recommended" engine like in the 350h, but I typically used regular gas most of the time. Where I needed to use premium was on the occasional cottage country trips on 2 lane roads winding thru mostly wilderness for hours. Unlike multi-lane highways, country roads that I drive would require max power sometimes to do quick passing before the next corner where I couldn't see oncoming traffic or what not. My RX on regular at full throttle I could feel the engine back off. Raise my foot off the floor to 90% throttle and I could clearly feel a boost of power. Using premium, no issue, full power right to the floor.

Even though I know the T24A engine has variants (with who knows what tuning differences) that can use regular gas, I've been too concerned to even try regular in my NX350. I find myself exploring the NX350's "potential" more than I ever bothered to in my RX. The RX could "go", but it did so without joy. The NX has joy. My insurance app went from all happy faces with the RX to a mix of frowny faces in the NX.

I may have made a mistake LOL

 

I use to be only into Muscle cars , then performance cars, then I got into the high mpg with a 1985 CRX HF and then hybrids. Anyway now I have hybrids and I kept one performance car, a Race Red 2018 Ford Focus RS. It is a 6 speed manual , AWD ( rear wheels are individually clutched), twin scroll 2.3 turbo rated at 350 hp and 350 ft lbs torque. It runs basically the same performance with 87, 91 or 93 Octane. Most of the time I just put in 87 regular. I still put the requisite oil in it though 0W50

I have always liked Lexus as my Luxury go to and even had one perfromance 5-speed manual IS300. ( yes bright red), my second manual shift Lexus LOL. Then I went to Prius, then I went to Lexus high mpg Ct200h, and finally Lexus Luxury cruiser, loaded NX 350h. I run regular in the Lexus NX 305h, RAV4 Hybrid Limited, Avalon Hybrid Limited and Gen5 Prius LE.

YMMV,
MidCow3