Only time i really see a difference between regular and premium is when im out west loaded down with gear and up in elevation. Not so much on my day to day driving here in the southeast.

What do you notice at elevation? I feel less power and better fuel economy in general here from 5,000’ up. Not sure octane would change that, but curious what you observe.

I have heard others on this forum say they have less head noise and smoother idling on this particular engine with 91. I haven’t tried 87 yet to check into it. I do have access to ethanol free 87 so I may check.

Your fuel gauge moves from Empty to Full.

I've been running 91 when I am pulling a trailer. I cannot tell any difference.

There's a lot to it. But the simplified answer is that it's a combination of design choices - the shape of the combustion chamber (piston and head), very good cooling system performance, the atomization of the fuel, the relatively low rpm limit, and the tune that runs on the rich side and doesn't advance timing too far. All of those work together to keep cylinder temps low enough that the air/fuel mix doesn't ignite too early. It also doesn't push the performance envelope at all. It never gives you 100% of what the engine could produce if it were tuned aggressively for high octane fuel.

Idle is probably the hardest condition to manage on modern engines. IIRC OV tuning said that half of the entire ECU's fuel map on the Tacoma 3.5L is only used during idle to keep it from knocking. It may be the same for the dual vvti 1GR. Maybe 91 octane will idle better???

Spot on.

The higher the octane number, the slower the burn rate.
Instructor at the automotive trade school I attended in 1978 did a demonstration.
In a long (4 foot if I recall) clear tube he atomized a drop or 2 of regular gasoline. Then ignighted it and you could watch the flame front travelling the length of the tube.
He repeated with high octane and the flame travelled significantly slower.

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People seem to think a higher octane somehow burns in a way that produces more power simply because performance vehicles require it to make the advertised power numbers. 91 is 4 more than 87 so it's better.

I believe it was Sport Compact Car that tested the high octane theory on a 2000s Honda Accord V6 that only needed 87. It consistently lost 10hp at the wheels when running 91.

This makes no sense to me. Knock is load-dependent, and there is no load at idle. I've never heard an engine knock at idle, and that includes old-school carbureted engines with no timing controls and plenty of advance. In fact, the only reason advance mechanisms were necessary before computers was to prevent kicking back during start-up. Once running, the engine could tolerate tons of advance without knocking as long as it was not under load.

The most challenging situation for managing knock is low RPM, high load (i.e., "lugging"). Low RPM, low load with the throttle closed shouldn't be a problem for any engine.

Any tests on a dyno or just what is observed? That's what would give us real insight on this.

The reason high performance engines require higher octâne is because they have hotter spark which produces a precise heat at the correct compression stroke to ignite the gasoline. lower octane will cause pre detonation or knock in those motors. Higher Octâne reading does not make more power it is the rate of burn at a given compression or detonation. Higher octâne fuel in lower compression engine will not increase power or mpg.
lower octane fuel in higher compression engine will produce knock or pinging. If your truck pings or knocks at idle with 87 then by all means use 89, 91, 95 or 98 but it is not going to increase your mpgs or add power.

Definitely the most noticeable is the reduced power up in elevation, and loaded down with gear I think it makes it more noticeable. This is all interstate driving, after I hit the trail I don’t notice any difference between the two.

You’d think it would have been settled long ago with a dyno, but I’ve asked several times and nobody has anything.

Read somewhere it took 3 full tanks of gas to adjust the timing for high octane = about 1000 miles. I do believe in pure gas (no ethanol). Pure Gas is mainly sold as 91 octane around here. Sure, I can't really tell if there is a difference with 91 octane. I don't have data. I also think it helps to use the entire rev range when using high octane. Driving all day at 2,200 rpms is not how the engine adjusts to high octane. The engine wants to rev to adjust timing. This is my opinion. I don't have proof and want that to be noted. 91 octane was $3.44 here today. I don't drive a lot of miles. Using 91 does hurt the pocketbook when traveling, however.

Also - I agree the purpose of high octane is to reduce pre detonation = ping/knock.

What about lugging up an incline and deciding whether to downshift or not? Assuming no change in pedal input, doesn’t the timing first advance as far as it can before the the transmission attempts to downshift?


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