Understanding Octane Ratings

[steelblue5505]

Re: Understanding Octane Ratings

Thanks everyone for your more than intelligent & informative replies.

Did anyone ever answer the original question........

Minimum Octane Rating
R+M/2 method.

Question: What is or does the formula mean, what is R what is M?

[05BlueBird]

Re: Understanding Octane Ratings

If you will google "octane rating" and read the definition by "wikipedia", maybe that will help or confuse you more like it did me

[lostjohn]

Re: Understanding Octane Ratings

I was told that that Mid grade 89 is blended at the pump from Premium 91 and Regular 87. Is that correct ? John

[007Cruiser]

Re: Understanding Octane Ratings

Thanks everyone for your more than intelligent & informative replies.

Did anyone ever answer the original question........

I believe it was answered indirectly. The formula represents an average of the Research Octane Number (R) and the Motor Octane Number (M).

[2k03birdman]

Re: Understanding Octane Ratings

Jon that is correct at some stations, some have a seprate tank just depends on how they were set up when the place was built. The reatail oil company I ran for a year blended it at the pump.

[Rondor]

Re: Understanding Octane Ratings

Frits, Europe measures octane using the RON method. We (US) use the R+M/2. Your numbers will be higher for the same octane rating.

All of California, Nevada, and Arizona have only 91 octane as Premium gas.
For all practical purposes, there is no difference other than to say that there may be more ethanol in the 93 stuff.
Remember, all gasoline starts at the same point. They only refine one gasoline.

Then additives are added to raise the Octane rating and keep the system clean.
There is no more "power" in 93 Octane than there is in 87 octane as measured by BTU available.

But the 93 Octane allows the ECU to advance the timing of the engine without knocking, and yes, when you advance the timing, the engine produces more HP.
So there may be 7 or 8 more RWHP when comparing 93 to 91.
That few HP is insignificant and is largely theoretical since most dynamometers can't repeat the same readings twice.

What will happen if you use 89 octane in our Birds?
Nothing. I did it. No knock.The Senors and the ECU did what they are designed to do.
Possibly it might take a few tenths of a second more to get to 60MPH, but the engine will not knock and will not be damaged.
The ECU will retard the timing slightly to prevent knocking.

What about 87 octane?
I don't know.
The Ecu, combined with Knock Sensors, can adapt for less or more octane, but obviously there is a range limit.
I strongly suspect the car will run just fine on 87 octane (Tho give up a more significant amount of performance as the timing is retarded) but somebody else will have to test that theory! ;)

Anyway, running the "proper" octane rating in an engine will often only cost pennies.....and return a bit more power and a bit more MPG......thereby offsetting the few pennies.
In Florida I run 93.
When I go to CA I will run 91.

You are 100% right and most times today you can't really be sure what you are getting at least Brand wise. I run premium and mid bith with no noticeable difference. The spread use to be 10 cents per grade but not true any more. Premium here jumps about 24-28 cents per gallon

[FEsTbird]

Re: Understanding Octane Ratings

91 is the high-test number in California.