Max707

Toys4RJill

You can also have knock without hearing it. There are different grades of knock. Knock sensors wear out as well.

Htony

Knock sensors can detect knock occurring beyond our hearing range. They are Piezo transducer(in other word; microphone) If any one who says car engine behaves same regardless of fuel grade, (s)he is just a green vehicle operator. I can even tell the difference between same grade fuel from different brand. I stick to Shell premium and always try to fill up at busy gas station for fresh fuel. If I do the same with Esso premium it feels different as well as smells different at the tail pipe. I am a driver, not an operator. Which one are you? Today's engines are mostly GDI type which make it important using top tier gas, oil. and proper PCV function to keep the engine running at peak performance level. Driving a vehicle is business of using all 5 senses always.

Htony

Did you take basic thermo dynamics in school? subject here is about engine performing at optimum level per design specs. using designated fuel grade. If owner's manual states fuel requirement, just follow it. If you ever towed with your truck you'll understand about this more readily. I used to tow 7500 lbs. fifth wheel driving at sea level up to high altitudes in the Rockies. I live in Foothills region. Experience is a good teacher....
How about taking the heads off your engines, take a look, see. Again experience is a good teacher.

Htony

Physically same engine, tuning parameters are not same. IMO, that is the reason.. For an example 2 Liter turbo engine VW uses, depending which vehicle it is going in, it can be tuned to produce ~250 Hp or ~200 Hp. Other manufacturers do the same thing. I'd think LX570 is classified as semi truck vs. Tundra is real truck made to deal with heavy work load. I bet their tranny. gear ratio are spec'd different too.

ClaytonW

At least LC and LX use the same engine (identical parts) and I am almost sure that there is no difference how the engines are tuned. It's just a stupid marketing. Premium car - premium fuel (like in other premium cars where the high octane fuel is really needed). Lexus or Toyta will not give you a specific answer if you ask them (I tried it). I think that they worry a class action lawsuit from LX owners if they admit that these engines are the same and there is no reason for the premium fuel.

Htony

In olden days brochure used to show detailed engine specs. Now all they show is Hp and Torque ratings. We can't readily see piston stroke, cylinder bore, cam shaft profile, power band, stuff like that. Any how every vehicle in my family uses premium gas per owner's manual. Only son-in-law drives 2017 4 Runner which uses regular gas. I guess if we get service manual, we can see what we want to see in there. Nowadays some owner's manual, service manuals are made into CD format.

Max707

I6turbo

iTrader: (1)

You may have misread the subject. The subject is "Premium fuel really needed?" Whether or not there's an actual need for 91 Octane or higher.
I've owned about 40 vehicles in my life from simple, old-school hot rods to modern performance cars to 18 wheelers, and just about everything else. I do all my own work, never taken one to a shop except for a few free things like warranty work, and a hand-full of alignments. I'll follow the manual if I think I should, not because someone on the internet recommends that I do what they do. Since about 2003 I've been running my Supra on the stock short block (ported head, aftermarket camshafts, fuel system, and other modifications) in a state of tune that makes more than 850 HP from 3 liters. For THAT engine, I run at least 110 Motor octane, and often higher. No premium in the LX or GX, though.

Here's something further on the subject of why manufacturers recommend higher octane (but I won't go into detail, it being Christmas night, me having things I want to do instead....)
A modern engine of good design, in good condition, that's been burning good quality fuel, actually requires several octane points LOWER than the manufacturer states in the "manual." The REASON for this "discrepancy" between what the manual says and what the engine actually needs is that manufacturers specify the octane requirement for a new vehicle based upon what the condition of the combustion chambers might be after the vehicle accumulates several tens of thousands of miles with less-than-ideal quality fuel. Or what it might need after the engine is older and perhaps has started burning some oil (which will very likely lead to deposits)

The primary determiner of octane demand ends up being the temperature that the air/fuel charge reaches before it is ignited by the spark (I won't go into why, but it is). In a clean engine ( that is, "clean" combustion chambers), the temperature that the air/fuel mixture reaches will be relatively low because a lot of the residual heat from the previous combustion event is dissipated through the valves, piston top, and the rest of the cylinder head surface inside the combustion chamber. In this clean engine, when the new charge of air/fuel mixture comes into the cylinder, it doesn't soak up too much heat from the combustion chamber surfaces because they've "cooled" down a good bit. HOWEVER, in engines that burn oil, or that have burned a lot of fuel that is prone to leave carbon deposits, there will be an insulating layer of deposits on these heat-sink surfaces. This layer retains much more heat than does bare metal. Consequently, the fresh air/fuel mixture gets heated several degrees more than it would in an engine with little or no deposits inside the combustion chamber. The result is that the fuel needs a significantly higher anti-knock index, a.k.a., higher octane in these old/deposit-laden engines.

Manufacturers cannot afford to develop a reputation of their engines pinging/knocking/crapping out when they reach 100K miles (or whatever) simply because they've been burning poor quality fuel or for some other reason have developed some deposits inside the combustion chambers. If they did, the resale value of their vehicles would be in the toilet. Therefore, they rate the octane "requirement" high enough that even an older engine in not-so-great condition will be okay with it.

The then-R&D manager for the company that developed Techron back in the day is an acquaintance of mine. He is mostly retired now, but is one of the worlds foremost authorities on fuel additives, including octane boosters. He gave me my my understanding of the OEM octane "requirements" thing. Now you know (unless you choose not to believe.)

I've towed plenty - 5th-wheel trailers with earth-moving equipment (very heavy) and livestock trailers (only about 13K pounds). I've built engines specifically for some of those pulling trucks. But that's irrelevant here because the subject is whether or not premium fuel is needed for a 200 series LX 570.
No thank you. I've built a bunch of engines so I've had the head(s) off of plenty, but I don't expect to need to take a head off of the LX.

Dimcguy

ClaytonW

Maybe, we should ask a different question. Or two questions. The first one is: Are the LC and LX engines parts identical? I think that some people already spent time and figured out that the answer is yes. The part numbers on all the engine parts are the same. There is no difference. The second question is: What about the software and the settings? Even if the software is identical, there can still be differences in its settings. I don't know the answer. But I would bet that there is no difference. But, who knows... I would be very happy if I could get an answer for this question from Toyota.

Toys4RJill

Htony

Yea, but modern engines are new breed engines applying GDI, two stage turbo, variable compression turbo, etc. Like today's vehicles are more electronics related than mechanics. Old shade tree mechanics, grease monkeys there nothing much to work on engines without knowing basic electronics. We are living in the era of digital electronics, AI logic, Nano tech, etc. Maybe we are in same age group. I'll be 78 in the new year.
Back is in EE. Retired almost 20 years ago from one company I worked for since I returned from overseas work frog hopping the globe. We have to move on based on the old knowledge we gained for newer technology. Being old is not an excuse not to learn new things. Again if owner's manual says use premium gas, just use it. I bet guys who designed engines know better than we do. Hyundai built a engine for new Genesis(of course GDI, turbo) they are worrying about reliability issues. That's rumor I heard coming from my home country Korea. I understand engineers are working hard to eliminate bad effect of using GDI
technology. BTW, GDI was invented by Bosch in the 30s. They used GDI engines to prevent fuel starvation problem using carburetors. VS. British woman engineer invented modified carburetor which elimnated
fuel starvation during dog fight. They used it on Spitfires.

lexusrus

So true.

Sometimes when I go fill up our LX570 by myself.......Sometimes I just use the cheapest 87 octane gas. Sure enough, when my wife drives it, she knows and can tell the difference!!!!

I6turbo

iTrader: (1)

Nice ramble there, but none of that has anything to do with the actual octane requirement of the engine in the LX, except the fact that the electronics can detect and adjust for the lower octane in the (unlikely) event that the engine encounters a condition where 87 isn't enough to allow 100% of rated output.