87 vs 91 Octane: LC vs LX570 (1 Viewer)

[CLHickman]

The conversation is easy right now. The argument that the cost is negligible is spot on, so why do we care? But.... What happens when fuel prices go upward of $4 a gallon again? Do we then say "maybe 87 octane and saving $8-10 each fill up is worth it?" This is especially a good question for those folks that fill up once a week, if not more...

Like many have already suggested, this topic is covered often. The search function will produce over 900 posts relating to fuel.

First hand experience...I've been running 87 octane in my LX for over 10,000 miles and have noticed zero difference. That is based off 10,000 miles with 93 octane.

 

[Reckless]

This thread helped me convert from 93 to 87. I would like to thank people for writing their views as it was important in order to convince me that there was no difference. I don't feel comfortable putting 87 in my twin turbo V12 but in my land cruiser as it was designed to run in places with poor quality fuel it doesn't seem to make a difference.

 

[FinallyGotOne!]

^^^ Well said!

 

[TeCKis300]

All our conjecture and anecdotal evidence is really immaterial.

These are the facts and you can decide as you wish.
1) The LX was tested and validated with 91 octane fuel. This resulted in 2 more hp than the LC. It obviously has the necessary tuning to take advantage of higher octane fuel resulting in incrementally more efficiency and power (that is more than likely offset by it's weight disadvantage due to higher standard level of features).
2) The LC was tested and validated with 87 octane fuel. It's target/optimal map is designed for this. The ECU likely has more aggressive and less aggressive maps, or compensation maps it can take advantage of for different grade fuel.
3) It is important to understand how an ECU compensates for lower grade fuel. It doesn't measure the fuel directly to know. It indirectly compensates by listening to the knock sensors. Therefor, an engine will have to knock first, before the ECU knows to back off on the timing to a more conservative map. It will consistently and regularly try to advance timing to know if premium fuel has been put in. And it again senses knock, will back off to the more conservative map. This knock is not engine destroying knock obviously. It's low grade knock, but knock just the same. One can probably understand that knock is more stress on the engine than no knock.

People pay lots of money for mods that make more power from 3rd party companies. Where claims should be taken with a big grain of salt (i.e. airfilters, tornadoes, etc.) I find it funny that people that have paid for such an expensive rig, would pinch pennies on fuel. And probably pay many for questionable mods.

 

[Markuson]

All our conjecture and anecdotal evidence is really immaterial.

These are the facts and you can decide as you wish.
1) The LX was tested and validated with 91 octane fuel. This resulted in 2 more hp than the LC. It obviously has the necessary tuning to take advantage of higher octane fuel resulting in incrementally more efficiency and power (that is more than likely offset by it's weight disadvantage due to higher standard level of features).
2) The LC was tested and validated with 87 octane fuel. It's target/optimal map is designed for this. The ECU likely has more aggressive and less aggressive maps, or compensation maps it can take advantage of for different grade fuel.
3) It is important to understand how an ECU compensates for lower grade fuel. It doesn't measure the fuel directly to know. It indirectly compensates by listening to the knock sensors. Therefor, an engine will have to knock first, before the ECU knows to back off on the timing to a more conservative map. It will consistently and regularly try to advance timing to know if premium fuel has been put in. And it again senses knock, will back off to the more conservative map. This knock is not engine destroying knock obviously. It's low grade knock, but knock just the same. One can probably understand that knock is more stress on the engine than no knock.

People pay lots of money for mods that make more power from 3rd party companies. Where claims should be taken with a big grain of salt (i.e. airfilters, tornadoes, etc.) I find it funny that people that have paid for such an expensive rig, would pinch pennies on fuel. And probably pay many for questionable mods.

I think you were a little liberal in your use of "obviously."

There is nothing documented to determine that octane is the difference, or if it is...whether the LC might also register that minuscule 2HP increase as well. Nothing is obvious about whether the LX is tuned differently unless that is stated somewhere by Lexus/Toyota.

As for knocking... You are assuming there is knock with 87. Can you verify that there is knock it's having to adjust for? Or...is it simply behaving exactly the same as the 5.7 in the LC, and there is no difference in level of knock?

One man's obvious is another man's question mark. I'm in favor of question marks until there is evidence.

 

[JtBrown]

For the $4 extra I spend on 93, I know my ecu is working a lot less lol!

Last thing I will say 381 hp/401 tq is a lot of power. May not be required but this is not a Prius motor.

 

[TeCKis300]

I think you were a little liberal in your use of "obviously."

There is nothing documented to determine that octane is the difference, or if it is...whether the LC might also register that minuscule 2HP increase as well. Nothing is obvious about whether the LX is tuned differently unless that is stated somewhere by Lexus/Toyota.

As for knocking... You are assuming there is knock with 87. Can you verify that there is knock it's having to adjust for? Or...is it simply behaving exactly the same as the 5.7 in the LC, and there is no difference in level of knock?

One man's obvious is another man's question mark. I'm in favor of question marks until there is evidence.

Perhaps what's obvious to me may not be to the general population. I have quite a bit of experience tuning turbo Lexus's and Porches. So I've done my share of staring at real software maps and logging outputs. ECU systems are quite sophisticated in their ability to register the slightest hint of knock and ride the line of greatest efficiency just shy knock. Octane is a primary variable in how much timing can be run, and how much power can be extracted given a fixed compression ratio. This is a well understood concept in engine tuning that is real.

The LC vs LX would not be the first example of sister drivetrains that use different calibration, tailored for their application and target audience. Redbull touched on it earlier. You would be in minority POV on a sports car forum. And not without reason as those forums do focus and analyze evidence for the benefit of added octane.

I'd expect any modern 91 calibrated car to be able to run on 87 without long term harm. Though would I if I had a choice? I've seen the real knock log differences between 87 and 91. Let me ask, would you fill 87 if you owned a Porche that asked for 91? The LX is not exactly cheap either. I for one wouldn't put 87 in my LX on a regular basis just to save a few bucks.

 

[TeCKis300]

It seems pretty clear cut from the manual what's best for the LX.

Per Lexus LX 570 instruction manual, p 684.

"Premium unleaded gasoline only"
"91 (Research Octane Number 96) or higher"

Then we have another gasoline tidbit on page 692:

"If 91 Octane cannot be obtained, you may use unleaded gasoline with an Octane Rating as low as 87 (research octane number 91). However, use of unleaded fuel with an octane rating lower than 91 may result in engine knocking or drastically reduce output to protect itself while driving a heavy load. Persistent knocking can lead to engine damage and should be corrected by refueling with higher octane unleaded gasoline."

Also, on page 692, it says:
"Premium unleaded gasoline with an octane rating 91 or higher required for optimum performance."

 

[TonyP]

Perhaps what's obvious to me may not be to the general population. I have quite a bit of experience tuning turbo Lexus's and Porches. So I've done my share of staring at real software maps and logging outputs. ECU systems are quite sophisticated in their ability to register the slightest hint of knock and ride the line of greatest efficiency just shy knock. Octane is a primary variable in how much timing can be run, and how much power can be extracted given a fixed compression ratio. This is a well understood concept in engine tuning that is real.

The LC vs LX would not be the first example of sister drivetrains that use different calibration, tailored for their application and target audience. Redbull touched on it earlier. You would be in minority POV on a sports car forum. And not without reason as those forums do focus and analyze evidence for the benefit of added octane.

I'd expect any modern 91 calibrated car to be able to run on 87 without long term harm. Though would I if I had a choice? I've seen the real knock log differences between 87 and 91. Let me ask, would you fill 87 if you owned a Porche that asked for 91? The LX is not exactly cheap either. I for one wouldn't put 87 in my LX on a regular basis just to save a few bucks.

My Porch prefers Behr Premium patio paint.

 

[Taco2Cruiser]

It seems pretty clear cut from the manual what's best for the LX.

Per Lexus LX 570 instruction manual, p 684.

"Premium unleaded gasoline only"
"91 (Research Octane Number 96) or higher"

Then we have another gasoline tidbit on page 692:

"If 91 Octane cannot be obtained, you may use unleaded gasoline with an Octane Rating as low as 87 (research octane number 91). However, use of unleaded fuel with an octane rating lower than 91 may result in engine knocking or drastically reduce output to protect itself while driving a heavy load. Persistent knocking can lead to engine damage and should be corrected by refueling with higher octane unleaded gasoline."

Also, on page 692, it says:
"Premium unleaded gasoline with an octane rating 91 or higher required for optimum performance."

Reminds me of my 07 FJ, manual said the same thing. Even though the 4.0L single VVT-t engine was the same as in all 2nd generation Tacomas and 4th generation 4Runners that required 87, mine wanted premium. Then the tests began... every switch of fuel over thousands of miles between me and my friends tacoma proved 87 to 91 didn't change anything. Then we dug into the engines, they ran the same timing, regardless of octane, they ran the same everything. Okay, must be mapping, tapped into that with my UCON-EMS, and the same again. Never could figure out why I needed Premium, so I stopped. Nothing changed. Lived in El Paso for a few years where regular is 86 octane, nothing changed. Lower octane at elevation is a hold over from carb engines that had to be tuned before heading up in the mountains, and gas companies use it to get people to pay for mid grade. Modern engine, hell our engines have altimeters in them to adjust. So even if Lexus wants you to feel like you belong alongside the V12 supercar at the pump loading it up with only the finest of refined crude oils because of image, know you don't need it.

Besides, that manual says minimum octane of 91 right? So why not 110? (non leaded of course). Got to be better if the ECU can make all the changes needed, right. Wait that's crazy talk!!

Now I'll give you one, I filled up with 12 hour old freshness, non ethanol, VP race fuel C9 red colored gloriousness 97 octane that is also scientifically proven to stop engine knock, sticky valves, terrorism, and gingivitis, and I didn't have to unlock the torque converter on a hard pull up a windy west texas highway that I normally do. But with pump gas 91, nope.

 

[ConcreteCruiser]

These 5.7 liter low compression engines are completely different from high compression turbo engines which indeed need higher octane fuels. All past models of the LX vs LC have interchangeable engine parts. I'm not sure about the LX570 but if the ECU map is the only difference, I think I would still lean towards using 87. If the LC was filled with 91 octane, would it also produce 2 more hp? If so, I would think the ECU's are also the same with the same maps. In my LX450 the only differences from the LC were the body panels, leather and a couple amenities. It takes 87 octane. Even after 20 years, I doubt Toyota would alter the mechanics of their shared Lexus engine. The engine and ECU are probably all the same. In other naturally aspirated engines, higher octane fuel will also produce slightly higher hp, as with BMWs. The tuner who wrote above here made some great points. I still need evidence that there's a physical or mapping difference between the two to justify the 91 octane. Quoting the manual is helpful but too linked to the marketers to convince me. I appreciate all the informed responses, but I'm still not sure what to do!

 

[SC200]

From my 2016 LC manual - in addition to octane 87 or higher requirement. I noticed this section on recommended gasoline.

What do you all think concerning the "top tier detergent" strong recommendation??

■ Recommendation of the use of gasoline containing detergent additives
●Toyota recommends the use of gasoline that contains detergent additives to avoid the build-up of engine deposits.
●All gasoline sold in the U.S.A. contains minimum detergent additives to clean and/or keep clean intake systems, per EPA’s lowest additives concentration program.
●Toyota strongly recommends the use of Top Tier Detergent Gasoline. For more information on Top Tier Detergent Gasoline and a list of marketers, please go to the official website www.toptiergas.com.

 

[ConcreteCruiser]

I've seen the top tier recommendations with other cars and I'm inclined to believe theres a difference. Around here is usually just means Mobil instead of Sunoco. Top tier also includes Valero, Texaco, Shell and several others. So, I'm planning on using top tier, 87 or 91, but usually 87, I haven't even voted yet!

 

[TeCKis300]

Sorry all if I come off a bit strong. Just that I feel strongly about this subject. No one's going to likely kill their engine in the long rung by running 87. But I do strongly believe it's slightly more wear and tear. In reality, it's incrementally more cost to fuel with premium, but it's also incrementally better performance AND better fuel efficiency. It's not just throwing money away by splurging for that premium.

ConcreteCruiser, not looking to argue anything but you bring up some good discussion points.

These 5.7 liter low compression engines are completely different from high compression turbo engines which indeed need higher octane fuels.

No modern engine today is really low compression in the sense it was in the old days. Whether naturally aspirated or forced induction. Low compression would be akin to leaving fuel efficiency on the table. We all know how competitive OEMs are in trying to up MPG ratings. Which is why ECU's are so highly calibrated and sensitive to ride the boundary between extracting the most power (i.e. energy) and knock.

If the LC was filled with 91 octane, would it also produce 2 more hp?

Not necessarily. Because remember, an ECU would have to probe for higher fuel quality by overstepping that timing boundary into knock, to know that the good stuff is in the tank. If the ECU frequently probes that barrier, than it would also be more frequently stressing the motor.

Interesting fact about octane is that it is actually an ignition inhibitor. Higher octane fuels actually burn slower, and has just a tad less energy content. So an engine that is mapped for for 87, may actually lose power when run with higher octane fuels (because ignition timing is not sufficiently advanced to account for the slower burn rate). By the same token, a vehicle that asks for 91, needs to be have more advanced timing to start with, to actually benefit from the higher octane. Advanced timing that is non-optimal and likely to knock when run with 87...just like the manual says.

Without going too deep into technical discussion, I hope this helps you guys understand that octane is not simply a marketing construct. There are fundamental engineering aspects to accommodate when tuning for specific grades of fuel

 

[gaijin]

Because remember, an ECU would have to probe for higher fuel quality by overstepping that timing boundary into knock, to know that the good stuff is in the tank. If the ECU frequently probes that barrier, than it would also be more frequently stressing the motor.

Interesting fact about octane is that it is actually an ignition inhibitor. Higher octane fuels actually burn slower, and has just a tad less energy content. So an engine that is mapped for for 87, may actually lose power when run with higher octane fuels (because ignition timing is not sufficiently advanced to account for the slower burn rate). By the same token, a vehicle that asks for 91, needs to be have more advanced timing to start with, to actually benefit from the higher octane. Advanced timing that is non-optimal and likely to knock when run with 87...just like the manual says.

And the manual for my 2013 LC says:

Your vehicle must use only unleaded gasoline.
Select octane rating 87 (Research Octane Number 91) or higher. Use
of unleaded gasoline with an octane rating lower than 87 may result
in engine knocking. Persistent knocking can lead to engine damage.
At minimum, the gasoline you use should meet the specifications
of ASTM D4814 in the U.S.A.

From which I infer there is no detrimental effect from using 91 octane rated gasoline. Is it your understanding, then, that my LC's ECU is "probing" for higher fuel octane, and would adjust to accomodate? If not, wouldn't there be the risk of more stress/harm to the motor and Toyota would recommend against the higher octane gasoline?

Just curious.

 

[TeCKis300]

Knock (uncontrolled combustion) is the concern and is what stresses/kills engines. Especially under load such as accelerating aggressively, climbing grades, or towing.

As you infer, there is indeed no added stress on an engine from having too much octane. It just won't make the most out of the fuel. Said another way, it may make even less power, which in turn stresses the engine less.

 

[Markuson]

Here's another way of looking at it:

BUYING 87 gets you **FREE MODS**!!!

With that...I present my "Free Mod" angle.

Here goes...

-Buying 87 instead of 91 will save you somewhere in the neighborhood of $3700-$4,400 over a 200k mile ownership span.

That's 200,000 miles...divided by an overall average of 13.5MPG (reasonable) means you will buy 14,815 gallons of fuel.

If you save 25 cents a gallon (US Dollars) buying 87 instead of 91, you will save $3,703 dollars on fuel.
If the difference is 30 cents a gallon? -You'll save $4,444.

Some places charge as much as 40-50 cents a gallon more for 91 vs. 87 and worse.
At 45 cents savings on 14,815 gallons purchased...you will save a whopping $6,666 US dollars.

That's enough to buy a sweet bull bar, winch, rear bumper/tire carrier and sliders from Slee!

Bottom line:
BUYING 87 = FREE MODS!! (Or at least that's how I'll pitch to me wifey! Lol)...

Wooo! I love free mods!

 

[Angelo1]

My Costco is either 85 or 91 here in Colorado. I've only been averaging 13.8mpg using 85oct. Maybe I should use 91 to average 13.9mpg.

 

[TeCKis300]

My Costco is either 85 or 91 here in Colorado. I've only been averaging 13.8mpg using 85oct. Maybe I should use 91 to average 13.9mpg.

All in good fun.

There's actually an interesting reason you guys have 85 octane at all. It would very much be a waste to use 89, let alone 91. CO is at a pretty high elevation, where the air is much thinner. This effectively reduces engine compression as the motor can't breathe as deeply, and the engine operates further from the knock boundary.

 

[Angelo1]

All in good fun.

There's actually an interesting reason you guys have 85 octane at all. It would very much be a waste to use 89, let alone 91. CO is at a pretty high elevation, where the air is much thinner. This effectively reduces engine compression as the motor can't breathe as deeply, and the engine operates further from the knock boundary.

Thanks, I had no idea why they sold 85, figured Costco was just cheap...lol. Well, that makes sense as I've never had an issue with 85oct. I was starting think I should start using Mid grade