But is it true that it can make up to 15 hp more on 91+ octane? I see that thrown around, but I feel nothing and believe that a 5% gain would be noticeable.

No. Toyota would push that if it was real.

When did they start putting rear coil spring suspension on the 4Runner?

I don’t know. There’s a lot to consider that goes on in the background. Maybe using 91 and getting more power leads to less fuel economy and lawyers said focus on CAFE?

The higher the octane, the harder it is for the fuel to ignite that's why performance vehicles use it. The cylinder pressures are higher in those vehicles and would cause a lower octane fuel to ignite unevenly and or early (knock). There's no extra power to be had from it.

I also have a 2006 Tacoma 4.0 V6.

The Tacoma has more low end power and the 4Runner seems to have more top end power.

The 4Runner sometimes doesn't down shift correctly. Sometimes it won't downshift when I expect it to so that makes it seems like a complete dog. Other times it will drop too many gears at once and the engine will go to redline and take off like bat out of hell.

The Tacoma's engine and transmission seem to work very well together. The downshift seems to always happen correctly.

It wouldn't be uncommon for modern ECUs to have a variety or range of fuel/ignition/cam timing maps for different fuels. Using the knock sensor it could adjust to maximize power or efficiency for a range of fuel. My last Acura car was more explicit in the manual that any octane was fine, but on lower than 91 octane at a lower power output. It never said how much power you'd lose. Just that it would be less.

Toyota has used the exact same engine in Toyota and Lexus models with the Lexus rated on higher octane with a higher power number. But in the examples I know if - we're talking about 5hp difference. Not 15 or as much as 35 I've seen claimed. The 2GR-FE in the Camry vs RX350 for example. It was 4hp difference in rating.

Turbo engines seem to have more ability to capitalize on the higher octane. Car and driver tested a few and found as much as 20hp difference on the dyno between high and low octane gas. Is Premium Gas Worth It? We Test High Octane on 4 Popular Vehicles

FWIW - I buy the cheap stuff most of the time.

Fair enough. I feel certain someone has dyno’ed this engine and knows specifics.

The Dual VVT-i 1GR-FE, has more power throughout the rev range. Meaning from idle to redline, it makes more power than the single VVT-i 1GR-FE.

Their respective power curves show a bigger power increase for the Dual VVT-i 1GR-FE over the single VVT-i 1GR-FE as revs rise, as would be expected.

What the Tacoma has going for it in perceived power when pulling away from a stop, and indeed all the time, is a lighter curb weight.

For the last couple years I started putting 93 in the tank once the temps here hit 90+ degrees. It makes a very noticeable difference in city driving. With regular my truck would just bog down the closer the temps got to 100. Now it just zooms along effortlessly, relatively speaking.

I have no idea if it's increasing horsepower, I suspect the timing change with the higher octane is just more suitable.

I had a 2016 Tacoma for a year before buying the 4runner. A year was all I could handle. Especially city driving, felt more like I was driving a tractor than a truck. Talk about gear hunting on the highway too. They should have put the 8 speed in the Tacoma rather than the 6 speed. Think that would have solved a lot of issues. Still it's the best selling small truck so I guess some people don't care.

The 4runner is not perfect but it's pretty great.