Horsepower with 87 octane vs higher octane

It was likely misunderstanding from early documents using 91RON which is used in other countries and is equivalent to 87 octane in the US

 

We don't know and we won't unless some auto outlet actually digs into it and maybe throws one on a dyno.

I think there might be some truth to it because of the ability of Toyota's new Dynamic Force engines to be very aggressive in the variability of the intake valve timing. Toyota switched to intake timing controlled by an electrical motor rather than oil pressure. This allows for the timing to be advanced or retarded much, much more than previous versions. I could see a situation where high-octane gas would allow the car's computer to use the variable timing to increase compression just a bit to squeeze a little more power out of the fuel. If you're using lower-octane fuel, the engine would begin to knock a bit at the highest compression, so the computer would adjust the timing back a little to reduce compression and eliminate the knock.

 

In one of the videos Toyota released, there was a footnote about power and mpg ratings being based on 91 octane. Take a look at the Lexus site, and you'll a find a similar footnote under some models. Then I've seen the 91 RON to 87 AKI error on early Tundra window stickers.

 

With a little googling, I found what the OP probably saw, in a cars.com article:

https://www.cars.com/research/toyota-prius-2023/

"The previous Prius recommended 87-octane regular gas, but these numbers are achieved using 91-octane premium fuel. It’s not required for the Prius, but it’s what Toyota used to get these power and fuel economy numbers; if you want to achieve them, too, you’ll likely need to use more expensive fuel."

However, I also found this at SAE.org:

2023 Toyota Prius punches it up

"The new 2L engine’s hike to a 14:1 compression ratio led to concern about required fuel octane, but Toyota assured journalists at the media introduction that maximum performance is achieved on 87-octane regular unleaded gasoline."

So if I had to bet, I think my money would be with MalachyNG and a confusion between RON and (R+M)/2.

Anyway, it's still Atkinson, right? So that's a 14:1 expansion ratio.

 

I always thought the M stood for Motor. But, yeah.

 

@Tideland Prius spotted the footnote about octane.
My Concerns with the New Prius | PriusChat (post #14)

The UX, NX, and RX hybrids all have the same footnote at the Lexus site, as well as some of the turbo engines.

Toyota is very likely designing engines for RON. It is what most of the world uses, and research is showing that RON has more bearing on modern engine performance than MON.

"Recent literature suggests that MON is less important than RON in modern cars and a relaxation in the MON specification could improve vehicle performance, while also helping refiners in the production of gasoline."
Effect of Octane on the Performance of Two Gasoline Direct Injection Passenger Cars

"The objective of this study was to assess the significance of RON and MON to the combustion characteristics of a modern SI engine. A single cylinder 4-stroke direct injection spark ignition (DISI) research engine was used as the experimental tool. The engine tests were conducted at the engine speed of 1800 rpm and the engine load ranging from 4 to 20 bar IMEP. Three market representative engine compression ratios (9.5:1, 10.5:1 and 11.5:1) were selected. In addition, the engine K value was calculated at knock-limited engine conditions. The results showed that, under knock-free engine operating conditions and at a fixed engine compression ratio, variation of fuel RON and MON had almost no differential impact on ITE(indicated thermal efficiency). Under knock-limited operating conditions, increasing MON did not increase ITE, and in contrast, even led to decreased ITE especially when RON was as low as 93 and the compression ratio was high. Under knock-limited operating conditions, when the RON of the fuel was as high as 98, changing the MON up or down only showed combustion phasing benefits/disbenefits without obvious ITE benefit. This is because the octane rating of the fuel was high and in order to differentiate their anti-knock quality, a higher compression ratio than 11.5:1 was needed. The calculated engine K value shows that RON was a more significant influential factor than MON in determining the engine thermal efficiency."
Significance of RON and MON to a modern DISI engine - ScienceDirect

 

The basic problem here is:
Most people seem to think that higher octane fuel somehow has more energy content.
It does NOT.

So......in an engine not specifically designed for the higher octane fuel, it is plain and simply a total waste of money.

 

Ok, but the thread started off with a sincere question about whether this engine was "specifically designed for the higher octane fuel" or not.

I think the answer turned out to be that it is not, and the article saying it was had confused two different octane-reporting numbers. But the question was worth asking.

The article Trollbait found was interesting, because it seems to suggest the MON could be allowed even lower without adversely affecting modern engines. Of course if we in the US continue to put (R+M)/2 on our pumps while the rest of the world just shows R, then allowing M to be lower will mean even bigger confusing differences between the numbers on their pumps and the numbers on ours.

 

It was confusion started by Toyota themselves. Though I now think the footnote in the video is because Japan's regular grade is 90 RON. If there is any difference with using 87 AKI, it will likely be too small for most to notice.

About a decade ago, there was a push by the fuel industry to go to 95 RON for regular as a way of conserving fuel and lowering emissions. Came across it looking for a non-Wiki source to the 90 RON. Didn't get traction here.
https://www.acfa.org.sg/newsletters/jama-upgrading-regular-gasoline-95ron
It would work, if cars also had high compression engines.

The further add to octane rating confusion beyond cars, 100 octane US avgas is in RON. The more shocking thing is that it still has lead.

 

You were correct. That's been the case for many decades, since long before (R+M)/2 was a thing.

 

Gen 5 Prius/Prius Prime spec regular gas (87 octane in the US method). Yes, the method and numbers in other countries are different. The only effect of using mid-grade or premium gas in Gen 5 Prius/Prius Prime will be a higher fuel cost for the owner.

 

That is the likely outcome in this case. In others it may not be so, as marketing will apply regular to more... pedestrian models even if the engine is designed for premium.

1.4L turbo in the previous gen Sonic was a premium designed engine with a regular recommendation in the manual. There were noticeable improvements to fuel economy when using higher octanes. Wasn't interested in power output enough to try measuring it. For equal cost per mile, 93 octane couldn't be more the 25cents higher. So even an improvement meant higher fuel costs in most cases.