Ethanol has a higher threshold for detonation thus forced induced cars love it. The issue with ACN 91 is that it's 91 and full of special air quality "improving" additives that can rob performance. LOTS of late model turbo owners run a gasoline and E85 mix in their modified turbo cars, typically to get around E30-E50.

In a naturally aspirated, lower compression, and lower revving motor like the 4Runner, you're wasting your time running 91+ plus wasting a TON of money. Any improvement in power is mental.

I appreciate the sacrifice your wallet is making in the name of science

Wow, 7 pages of guessing and anecdotes...

Until measured with data collection, we won't really know what differences there are.

Car and Driver did a somewhat recent comparison on a varied set of vehicles. Now while there are some differences in the 4R with these, there is one big takeaway from this: not much is gained from higher octane in these run of the mill production vehicles. Even when there was improvement, it was not significant.

Is Premium Gas Worth It? We Test High Octane on 4 Popular Vehicles

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Sport Compact Car did a similar test on a Honda Accord V6 at the time (2000ish). Anytime they ran 91 the car consistently lost 10hp at the wheels. This was after running a couple of tanks through it back and forth between 91 and 87. So they would switch fuels and "let the ECU see it" as everyone claims.

Not surprised. Higher octane fuel is it's resistance to ignite. The 4G motor is not designed or tuned to the necessitate the need for higher octane fuel. Chances are it will result in marginally less power and lower mpgs.

That's interesting. And that's a monster drop off. 10HP on a 2000ish Accord is a big number.

I started to run 91 in my 2010 Tacoma because I had experienced some minor pinging at low RPM/high load situations (AC on and accelerating). Eventually I supercharged so I needed to run it anyway.

It was the 6th gen when the 2 door had the optional 3.0 V6 with dual exhaust. I have long since thrown out the issue but this has been a debate for years. People seem to think the ECU can see octane and change the tune enough to make more power but it wouldn't make sense for a manufacture to tune for a higher octane but recommend the lower octane.

Toyota did have "91 for better performance" listed in the early Tacomas (05/06) but it was removed probably because it didn't do anything.

I agree with you, but manufacturers do things like that. They sometimes opt to be stealth with respect to certain features/benefits/functions. For example, VW always understates its 0-60 times. In the 2022 Golf R, they say the 0-60 is 4.7 seconds. Literally every reviewer, be it Canada, US, UK, is achieving about 4.2. That is a big difference.

And does Toyota not say their transmission fluid is for "life?" It's not. Why would they do that? I'm not going to doubt a theory because I do not know the answer to why Toyota would or would not do something. Enough people are saying premium makes a difference to give me pause. It's a very large minority of people and they can't all be stupid or unreasonable (not saying you are accusing them of being stupid or unreasonable). I will try 91 for a while. I will feel a difference if there is one. I'm pretty in-tune with the vehicles I drive regularly.

There's not truth to this


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Toyota has since modified the maintenance interval with the trans fluid. Also Toyota doesn't underrate their modern engines. There's no need because people buy their product anyway. The ECU cannot see octane since there's no sensor for it. No the knock sensors do not see octane, they see knock and if there is none then all is good. This doesn't put the ECU into "make more power because this guy put in the good stuff" mode.

Don't feel anything, get it scientifically proven with a dyno.

I decided to go back to the manual. I actually went back and looked at the manuals for all naturally aspirated vehicles I have owned. None of them actually state, explicitly, that 87 is recommended. All the manuals state to use 87 or higher.

This can mean a couple things:

(1) Use 87, but if 87 is unavailable at your station, then there is no problem using 89 or 91; or, (2) While 91 will be best, your vehicle still accepts 87.

The thing is, when it comes to disclosures and things of this sort, and they become sort of boiler-plate or standardized, companies won't change them. It makes zero sense to, even if there is useful information (like 91 may increase performance/MPG/longevity) being withheld from the end user. I'm going to take the fuel in my tank down to a point where I have like 3 miles left before empty, and fill it with 91. I want as little "taint" as possible in my tank filled with 91 lol. Can't wait to try this. Too bad I don't drive the 4Runner much. Could be a week or 2.

What's more is that all the 91 users claim better MPG. Like in the 19-21 range. That makes no sense. The standard Toyota uses to measure MPG means, in theory, you should not average anything above 18.999999 MPG (unless you're violating traffic laws).

Some states do bot use ethanol in their 91 or higher grades. That would increase mileage.

PLEASE do not confuse the DUAL VVTI system timing (it increases VALVE duration above 3500ish rpm); with IGNITION timing, which is controlled by the ECM. The two systems have (almost) NOTHING to do with each other.

The Toyota 4runner DOES NOT have a "gasoline quality sensor" for lack of a better term. SOME cars (Mercedes, Porsche, Ferrari etc.) DO have this sensor...but NOT a 4runner. The ECM does not know what you just loaded in the tank.

The ECM works on an if/then flowchart sort of decision making process.
IT IS NOT CAPABLE OF "LEARNING" in the classic sense of the word.
IT is ONLY a series of "MAPS" and sensor data that enable it to control the engine.
The ECM uses sensors like throttle position sensor, O2 sensors, knock sensors, engine temperature sensors, Intake air temperature sensors, etc.
to guide the if/then decision making process.

Simple example: for S&G lets assume that your truck is pulling a 2500pound trailer at highway speeds, and you filled up with 83 octane 10% ethanol fuel.
We will also assume that you are driving between Dallas and Houston 75MPH
and it is mid August with an outside temp of 98 degrees.

What is the ECU doing in this scenario?

Well it depends on the sensor data...lets say that on a cool spring day with the same load and speed the ecu allows the truck 30 degrees of IGNITION timing...but today it is so hot that your crappy gas begins to knock, and the knock sensor now only allows 20 degrees if IG timing.
IF, AND ONLY IF you had bought 93 octane gas, you MIGHT not have had your engine knock and you would happily be cruising down the road at 75+ mph, swearing that 93 octane makes more power, instead of wondering why your 4runner "just isnt running very well today."

The 4Runner ECM is ALWAYS looking to give the engine MAXIMUM timing all the time. BUT, those pesky sensors, hot summer (and very cold winter) days, crappy fuel, driving style, clogged air filters ETC, ETC, ETC...
get in the way of all the timing, all of the time.


Takeaways:
The Dual VVTI system is RPM dependent and a mechanical system for high RPM power. Period. It is essentially independent of the ECM.
The ECM is NOT SMART. It MUST rely on sensor data to control the engine.
The ECM has NO WAY TO KNOW what fuel you are running.
The ECM does have a short term memory that is continually being overwritten by new data from the sensors. It MAY save that data (for a period of time) IF it detects a pattern. Perhaps used to access the last program MAP that was used.

As much as we love our 4runners, there is a tendency to praise our trucks for things it is not capable of; and blame our trucks for things it was programed to do, whether we like it or not...
AMLOR

Just throwing in my anecdotal experience to this thread.

I tow a 2000lb trailer with a 2017 4Runner that is at max payload. Having crossed the country several times with this setup, it is my experience that higher octane and less Ethanol make a significant difference. I will get as low as 8.5 MPG with 87 octane w/Ethanol and as high as 12 MPG with 93 octane. This is traveling the same terrain. Headwind/tailwind makes a difference too.

The power difference is probably least subjective when using cruise control. The truck downshifts so much with low octane fuels that cruise control is unusable even on relatively flat ground. When running the lower octane, I will settle for 5-15mph slower climbing large hills than with the higher octane (because I am monitoring transmission temps).

I've tried this experiment back and forth many times. Putting in higher octane is expensive, but we get better range and a safer trip.

EDIT: I mention octane, but it is quite possible that it is the Ethanol content making the difference. On a recent trip to upstate New York, a fill-up of no-name 93 octane w/Ethanol was awful and a 91 octane w/out Ethanol was the best power of the trip.

Your observations are completely valid. Ethanol is NOT your friend, regardless of the octane you select. The issue is that ethanol has only 2/3 the energy density of gasoline per gallon.
As you might guess, on a 20 gallon tank of 10% ethanol "gas"; you have 2 gallons of liquid (ethanol) by volume. Those "2 gallons" DO affect your engine power potential negatively.

While I have 4.88 gears, I ALWAYS tow with the highest octane fuel I can find and will pay for "real gasoline" when I can find it.
For reference, I tow a 4800lb Airstream with the 4runner. I tow in 4th gear at about 60-65mph, about 3200 rpm, and get 10.5 to 11.0 MPG doing it.
AMLOR