Here is a question for all you guys who excelled in chemistry class.

Octane rating is a product of motor octane and research octane added together then divided by 2.

Which of the two ratings produces more power? In many instances one of those can be much higher than the other.

Bob

Not a chemist, but motor octane is the only rating that counts, for our purposes.
Motor octane is derived through actual testing in an engine (motor), research octane is theory.

Octane requirement for a particular application is derived from a wide range of factors, and is a deep, deep rabbit hole to go down.

quote:

Octane rating is a product of motor octane and research octane added together then divided by 2.

R+M is simply a rating "method". Why they chose it for commercial purchasing I don't know. More middle of the road maybe. An average (averaging) method for an average requirement. May even been political within the industry?

Renegade 110 is closer to a 111, and 112 is closer to 113 VS sunoco and VP just saying

Higher octane fuel doesn't "make" more power, it allows higher compression and/or more aggressive ignition timing, which MAY make more power.

You can put 93 octane fuel in your wife's Honda Pilot and it won't make more power. It might even make less.

Higher octane allows me to increase the compression ratio in my 15:1 / 582. We race at an altitude track (Barona, Ca). I have been using a Grid to alter the timing map. Knowing how the octane rating for a specific fuel is arrived at is important. 112 or 115 is calculated differently between these various fuels, I've run (VP, F&L or Sunoco) depending on availability.

Bob

ps: OBTW: She drives a new Subaru Outback so yes, 115 doesn't work worth a s@@t.

Addressing the OP's initial question. What does higher octane actually provide, opposed to what it allows. Generally speaking, and this is a complex topic, higher octane is less volatile and can forestall detonation and pre-ignition.

quote:

Originally posted by RPROGAS:
Here is a question for all you guys who excelled in chemistry class.

Octane rating is a product of motor octane and research octane added together then divided by 2.

Which of the two ratings produces more power? In many instances one of those can be much higher than the other.

Bob

AI Says....

MON is more relevant to power output.
That’s because MON testing simulates high load, high temperature, and higher RPM—conditions much closer to what an engine sees when making power (especially under full throttle).

RON is more relevant to knock resistance under light-load cruising.
It matters for drivability and efficiency at lower loads, but not as much for maximum power.

So, if two fuels have the same AKI but one has a much higher RON and a much lower MON, that fuel may resist knock at cruise but could underperform at full load compared to a fuel with a higher MON.

quote:

So, if two fuels have the same AKI but one has a much higher RON and a much lower MON, that fuel may resist knock at cruise but could underperform at full load compared to a fuel with a higher MON.

Example:

One brand of C15 can arrive at the same octane as another brand but the MON and RON are different. Even though it is the same overall octane rating the tuning ignition timing and jetting (or air bleeds) can be different.

I've been working with different timing maps based on several factors, fuel brand being one. VP, Sunoco are different, their (C15's) are not equivalent. Fuel availability where I live is a challenge, this is California. Switching brands happens frequently (VP, Sunoco and F&L).

This was the reason for my original question.

Bob

Yea I think Sunoco has a much lower rating I have an old sunoco flyer and the RON for 110 is 114 but the Mor is only 106, and 112 is 115 and 109.