SW17LS

FYI...they are the same basic engine, but they lack the direct injection which is a considerable difference.

Devh

And they are lower compression for the most obvious reason.

Lexuslsguy

There are many theories about what will happen to a high compression V8 if you run lower octane fuel and the reality is not much. Not with modern engines. The knock sensors monitor continuously for pre-detonation whether you are running 93 or 87. It makes no difference as to how the computer works. When you run lower octane fuel timing is pulled. This amounts to a bit less power and probably a very minor drop in fuel economy.

91 or higher is also "required" on the ls430 and this has proven to be the same scenario. Many owners run 87 without any issues and have done so for years. If our vehicles did not have knock sensors it would be a different story. Again, the evidence supports that this "requirement" is really just a recommendation. Want maximum power and efficiency from a high compression V8? Run 93. Or even better. Run race fuel. Want to save a few bucks? Run 87. Either way it will not harm your engine whatever you choose.

Oldfart

Copy and paste:

DI stands for Direct Injection.

".....DI has a key benefit: By injecting fuel directly into the cylinder during the compression stroke, the cooling effect of the vaporizing fuel doesn’t dissipate before the spark plug fires. As a result, the engine is more resistant to detonation—a premature and near-explosive burning of the fuel, producing a knocking sound and pounding the pistons with pressure and heat—and can therefore operate with a higher compression ratio—about 12:1 instead of 10.5:1. That alone improves fuel economy by two to three percent...."

Devh

I know a two modern engines where the owners decided to go cheap. The end result was one blower motor and the other had the timing belt skip a tooth. At best damage occurs gradually which can manifest itself in shorter engine life.
When Toyota says " may cause damage " that's all you need to know to know better.

Devh

Yes DI is more resistant to detonation and therefore it allows manufactures to increase the compression ratios to take advantage of more peak efficiency however it raises the bar to the limit where it is still dependent on higher octane fuel. You could even make a case for getting better fuel efficiency with premium in a direct injection motor as a result.

Lexuslsguy

Unless the car was tuned or another malfunction happened the octane rating would not cause this. If you have a forced induction motor and the car is tuned to high octane fuel this is a different story. When it comes to the Lexus LS it does not hurt the engine. Absolutely no evidence has ever been shown that it causes any damage. If you can provide any please do. Personally, I run premium in my vehicles because they produce more power but I know many who do not and they suffer no ill effects.

NickTee

Do all of them have the same cams, same tune with identical timing, same intake, same heads, same injection type, same intake and exhaust valves, etc? There's a reason that one runs on regular and the other runs on 91 and it isn't some internet conspiracy theory that they're just trying to make more money.

NickTee

Running race fuel wouldn't do anything for performance unless you brought it to a tuner and had the tune altered for race gas. This is the same reason it doesn't make sense to run premium in a car that uses regular gasoline, it's simply not optimized for that octane level.

Devh

The burden of proof is not on me. Toyota says " may cause damage" I would think Toyota knows their engines considering they have done all of the long-term testing and simulations of this motor, and reach their own conclusions which they have published in the owners manual. Anything outside that scope is going against the manufactures recommendation which is fine in some cases but not when it comes to anything remotely related to detonation.
Until someone here does extensive logging with a knock monitor to prove otherwise it's a very dangerous territory to say it's fine when Toyota says something completely contradictory.
I think for better clarification because the topic is interesting we should contact Toyota and hear what they have to say on the matter in an official capacity.

Lexuslsguy

My point is that this same exact warning is put on both the ls400 and ls430. Go check out this side and you will see owners have been running 87 for years without ill effects. I'm sure many ls460 also run 87 octane. Believe me, if it really did damage to the engine this thread would be full of those who suffered from it and not just theories.

NickTee

Not only that, but not every engine is the same. Even if they did extensive logging, doesn't mean it applies to all engines. Using a generalization fallacy to justify saving a small amount of money for a very expensive item is just not smart.
I get it, these thread will likely always appear when it comes to non-performance cars that require premium: some people will always try to take the 87 octane route to save money.

williakz

FRN (Fuel Rewards Network) is a GREAT benefit, but it's for SHELL GAS ONLY. You can really knock down your gas costs when you couple the FRN card with BOTH a cash back gas card (like the PenFed one I mentioned) AND a 2% cash back MasterCard (like Citi). With the FRN card (free for the asking at Shell), 3c/gal is ALWAYS available and there are various shopping, dining, entertainment, etc. promotions that run all the time.

The way it works is you "link" any MasterCard to your FRN account. Then as you buy stuff, FRN per gallon discounts are automatically stacked to your account. This is why Nospin's discounts vary: he's automatically qualifying for some of the various promotions during the normal course of buying the stuff of life. Also, FRN now has its own MasterCard which supercharges the Shell gas discounts available (i.e. 5c/gal goes to 10 or even 25c/gal for same $100 purchase of groceries or electronics or whatever) though I don't have the card and don't know whether it's a decent card other than the FRN benefits.

When you go to buy gas (Shell ONLY), you swipe the FRN card before you swipe your payment card and the cumulative FRN discount is applied to whatever flavor of gas you get right there at the pump. Catch is: you use up the entire discount whether you pump ONE gallon or the max of TWENTY (so you better wait until she's REAL thirsty). I've had well over $2/gallon discounts stacked up back when gas was in the mid $3 range. It was cool pumping $70 worth of gas and only getting charged $20. With all cylinders firing, you get the 3c/gal base discount, all the cumulative per gallon promotion discounts for normal spending which itself is discounted a minimum 2% depending on category, and whatever does end up on your gas card receives a further 5% discount. So, bring on the turbos!

Oldfart

I do not think there is a conspiracy. If you ever tried pushing car using physical force from stand still you'd notice that the most amount of force is required just to get it moving, for example let's say it takes 3 human beings just to get car moving and once it is in motion one person is enough to maintain the movement.
Same for the engine the most vulnerable position is at lowest RPM (just google any torque curve) and that is where I need the most octane I can get, but when car is already in motion that is totally different I could easily get away with lower octane. I am in agreement with SW15LS when he says you own a luxury car enjoy it (at least for my driving style) but I also can see that it is possible to get away with using lower grade fuel without any ill effect depending on commute and driving habits.

NickTee